Nonmalignant Leukocyte Disorders

PRELIM HEMATOLOGY 2 JANUARY 2026 Chapter 26: Nonmalignant Leukocyte Disorders PRIMARY IMMUNODEFICIENCY DISORDERS  Gene therapy has shown promising results in clinical trials but is not yet approved in the United States.  There remains a significant risk of leukemic transformation with gene therapy.  Outcomes following HSCT have improved over the past decade, allowing survival into adulthood. (Inborn Errors of Immunity – IEI) I. GENERAL OVERVIEW  Primary immunodeficiency disorders, also called Inborn Errors of Immunity (IEI), are inherited disorders affecting the innate and or adaptive immune system.  As of June 2022, nearly 500 inherited IEIs have been identified.  Most IEIs are rare, but as a group their prevalence in the United States is approximately 1 in 1,200 individuals.  IEIs result from germline genetic abnormalities such as missense mutations, deletions, or frameshift mutations.  These mutations lead to decreased quantity and or quality of immune proteins.   Disease severity ranges from life-threatening conditions in infancy to manageable disorders diagnosed in adulthood. Classification follows the International Union of Immunological Societies (IUIS) system. BMLS 3B A. COMMON GAMMA CHAIN DEFICIENCY (X-Linked SCID)  Most common form of SCID.  Classified as T negative, B positive SCID.  Inherited in an X-linked manner.  Caused by mutation of the IL2RG gene located at Xq13.1. Pathophysiology  IL2RG encodes the common gamma chain used by interleukins 2, 4, 7, 9, 15, and 21.  These interleukins support growth, differentiation, and survival of T and NK cells.  Mutation results in defective signaling and impaired development of T and NK cells. Clinical and Laboratory Findings 1. SEVERE COMBINED IMMUNE DEFICIENCY (SCID)  Absence of thymus, tonsils, and lymph nodes.  SCID represents a group of IEIs affecting both cellular and humoral immunity.  Severe infections beginning within the first few months of life.  Patients show markedly decreased T lymphocytes, poorly functioning B lymphocytes, and hypogammaglobulinemia.  Decreased white blood cell count due to markedly reduced T and NK cells.  Normal numbers of B cells that are functionally impaired.  Failure to thrive and death before 2 years of age without HSCT.  Clinical symptoms appear in infancy.  Without treatment, most patients die within the first 2 years of life due to severe bacterial, viral, or fungal infections. Management  Allogeneic hematopoietic stem cell transplantation is potentially curative. PRELIM HEMATOLOGY 2 JANUARY 2026 Chapter 26: Nonmalignant Leukocyte Disorders B. ADENOSINE DEAMINASE DEFICIENCY (ADA-SCID)  Classified as T negative, B negative SCID.  Accounts for 10 to 20 percent of SCID cases.  Autosomal recessive disorder.  Caused by mutation of the ADA gene located at 20q13.12. Pathophysiology  ADA is involved in the metabolism of ATP and RNA.  Deficiency leads to accumulation of toxic adenosine and deoxyadenosine.  This results in profound depletion of T cells, B cells, and NK cells. Clinical Features  Neutrophil chemotaxis and phagocytosis are impaired. Clinical Features  Recurrent infections.  Autoimmune manifestations.  Thrombocytopenia with small abnormal platelets.  Increased risk of bleeding. Management  Diagnosis confirmed by WAS gene sequencing.  HSCT is curative with an HLA-matched donor.  Gene therapy is promising but carries a risk of acute leukemia.  Severe, recurrent bacterial, viral, and fungal infections early in life. 3. 22q11.2 DELETION SYNDROME  Skeletal abnormalities. (DiGeorge Syndrome)  Neurologic deficits.  Skin rashes.  Combined immunodeficiency with syndromic features.  Caused by a heterozygous microdeletion on chromosome 22q11.2 involving 1.5 to 3 million base pairs.  Loss of over 100 genes, including TBX1 and DGCR8. 2. WISKOTT-ALDRICH SYNDROME (WAS)  Classified as a combined immunodeficiency with syndromic features. BMLS 3B Clinical Features  Rare X-linked disorder.   Caused by more than 450 known mutations in the WAS gene. Variable thymic hypoplasia causing T-cell lymphopenia.  Congenital cardiac anomalies.  Craniofacial abnormalities.  Hypocalcemia due to parathyroid hypoplasia.  Failure to thrive, growth restriction, and recurrent infections.  Autoimmune cytopenias and neurodevelopmental disorders. Pathophysiology  Mutation leads to decreased expression of WiskottAldrich syndrome protein (WASP).  WASP is essential for actin cytoskeleton remodeling and immunologic synapse stability.  Defects impair T-cell function, reduce B-cell numbers, and diminish NK-cell cytotoxicity.  Regulatory T cells become dysfunctional. PRELIM HEMATOLOGY 2 JANUARY 2026 Chapter 26: Nonmalignant Leukocyte Disorders Prognosis BMLS 3B 5. CHÉDIAK-HIGASHI SYNDROME (CHS)  Survival is often less than 1 year without thymic transplantation or HSCT.  Rare autosomal recessive immune dysregulation disorder.  A study of HSCT from 1995 to 2006 showed 41 percent survival at a median follow-up of 5.8 years.  Caused by mutation of the LYST gene located at 1q42.3.  Graft-versus-host disease is common. Pathophysiology  Formation of giant fused cytoplasmic granules in leukocytes, platelets, melanocytes, and other cells.  Granules visible in granulocytes, monocytes, NK cells, cytotoxic T cells, and platelets on peripheral blood smear. 4. BRUTON TYROSINE KINASE DEFICIENCY (X-Linked Agammaglobulinemia)  Classified as an antibody deficiency.  Caused by mutation of the BTK gene located at Xq21.3 to Xq22. Pathophysiology  Impaired B-cell development.  Absence of plasma cells.  Marked decrease in all immunoglobulin classes. Clinical Features  Partial albinism.  Severe recurrent bacterial infections.  Neutropenia and cytopenias.  Easy bruising and mild bleeding.  Progressive neurologic impairment. Clinical Features  Symptoms begin between 3 and 18 months after maternal antibodies decline.  Recurrent otitis media, sinusitis, conjunctivitis, diarrhea, and skin infections.  Increased susceptibility to encapsulated bacteria and enteroviruses. Prognosis  High risk of hemophagocytic lymphohistiocytosis.  Most patients die before 7 years of age without HSCT.  HSCT improves survival but does not halt neurologic decline. Management  Lifelong immunoglobulin replacement therapy.  Most patients now survive into adulthood.  Gene therapy studies in mice reported promising results in 2012. Pseudo–Chédiak-Higashi Granules  Seen in acute myeloid leukemia, chronic myeloid leukemia, myelodysplastic neoplasms, and rarely acute lymphoblastic leukemia.  One study reported PCH granules in 5 of 20 children with AML. PRELIM HEMATOLOGY 2 JANUARY 2026 Chapter 26: Nonmalignant Leukocyte Disorders 6. CONGENITAL DEFECTS OF PHAGOCYTE NUMBER AND FUNCTION  As of 2022, 42 distinct disorders have been identified.  Affects neutrophils, monocytes, and macrophages.  Common features include recurrent bacterial and fungal infections, poor wound healing, and oral inflammation. B. DEFECTS OF MOTILITY: LEUKOCYTE ADHESION DISORDERS (LADs) Overview    A. CONGENITAL NEUTROPENIA  Defined as absolute neutrophil count less than 1.5 × 10⁹ per liter.  Characterized by early onset and recurrent infections. a. Severe Congenital Neutropenia (SCN)  Leukocytes, mainly neutrophils and monocytes, migrate from blood to infection sites by adhering to the endothelium and rolling along vessel walls. Adhesion molecules: selectins and integrins mediate this process by binding ligands on leukocytes. Diapedesis: high-affinity integrin attachment allows leukocytes to transmigrate between endothelial gaps. Defect: LADs are rare autosomal recessive disorders where leukocytes cannot migrate to infection sites. a. LEUKOCYTE ADHESION DISORDERS (LAD)  Autosomal recessive disorders affecting leukocyte migration.  Characterized by recurrent infections, impaired wound healing, and neutrophilia.  Absolute neutrophil count less than 0.5 × 10⁹ per liter.  ELANE mutations account for 50 to 60 percent of cases.  Bone marrow shows maturation arrest at the promyelocyte or myelocyte stage.  Caused by mutations in ITGB2.  Defective beta-2 integrins.  Long-term G-CSF therapy is standard.  Severe infections shortly after birth.  After 15 years of G-CSF treatment, the cumulative risk of AML or MDS is 22 percent. b. Cyclic Neutropenia  Caused by ELANE mutations.  Characterized by 21-day cycles of neutropenia lasting 3 to 5 days.  No increased risk of malignant transformation. c. Shwachman-Diamond Syndrome BMLS 3B i. LAD Type I  Absence of pus formation. ii. LAD Type II  Caused by mutations in SLC35C1.  Defective fucose transport and impaired selectin ligand formation.  Milder infections but significant cognitive and skeletal abnormalities. iii. LAD Type III  Caused by mutation of the SBDS gene.  Caused by mutations in FERMT3.  Presents with neutropenia, pancreatic insufficiency, skeletal abnormalities, and growth failure.  Defective integrin activation.  Increased risk of AML and MDS.  Severe infections, bleeding tendency, and osteoporosis.  HSCT corrects hematologic defects only.  Poor prognosis without HSCT. PRELIM HEMATOLOGY 2 JANUARY 2026 BMLS 3B Chapter 26: Nonmalignant Leukocyte Disorders C. CHRONIC GRANULOMATOUS DISEASE (CGD)  Caused by defective respiratory burst in phagocytes.  Due to mutations in genes encoding NADPH oxidase components.  Two-thirds of cases are X-linked, one-third autosomal recessive. LYSOSOMAL STORAGE DISORDERS (LSDs) INBORN ERRORS OF METABOLISM  Inborn errors of metabolism consist of approximately 1,450 disorders  These disorders are divided into 24 categories and 124 groups  Most are caused by single-gene defects  They primarily affect enzymes responsible for metabolizing substrates  Enzyme deficiency leads to accumulation of toxic substances, which cause clinical manifestations Clinical Features  Recurrent life-threatening catalase-positive bacterial and fungal infections.  Granuloma formation and inflammatory complications. Diagnosis and Management  Screening by dihydrorhodamine 123 or nitroblue tetrazolium test.  Confirmation by DNA sequencing.  Management includes long-term antimicrobial prophylaxis.  A 2018 review showed approximately 90 percent overall survival at 3 years after HSCT. D. ENZYMATIC WHITE BLOOD CELL DEFECTS: MYELOPEROXIDASE DEFICIENCY  Most common inherited phagocyte disorder.  Caused by mutations in the MPO gene on chromosome 17q23.  MPO converts hydrogen peroxide into hypochlorous acid in neutrophils.  Most affected individuals are asymptomatic.  Increased fungal infection risk occurs mainly with comorbid conditions.  Automated hematology analyzers using MPO may give inaccurate WBC differentials. LYSOSOMAL STORAGE DISORDERS (LSDs)  LSDs are a subgroup of inborn errors of metabolism  There are more than 70 inherited LSDs  Caused by single-gene mutations that impair:   o Production o Transport o Secretion of lysosomal enzymes Failure to degrade macromolecules leads to: o Storage of undigested substrates in lysosomes o Cell dysfunction o Cell death o Multisystem clinical symptoms All cells containing lysosomes can be affected PRELIM HEMATOLOGY 2 JANUARY 2026 BMLS 3B Chapter 26: Nonmalignant Leukocyte Disorders Classification of LSDs LSDs are classified based on the type of accumulated macromolecule, including:  Sphingolipidoses  Pseudobasophilia  Mucolipidoses  Mucopolysaccharidoses  Lipoprotein storage disorders  Lysosomal transport defects 1. MUCOPOLYSACCHARIDOSES (MPS)   MPSs are rare inherited disorders involving impaired degradation of glycosaminoglycans (mucopolysaccharides) Combined incidence in the United States is 1 per 100,000 live births Hematologic Findings    Peripheral blood films may show: o Metachromatic Reilly bodies o Acquired Alder-Reilly anomaly Affected cells include: o Neutrophils o Monocytes o Lymphocytes Bone marrow histiocytes may show metachromatic cytoplasmic material Diagnosis  Enzyme assays to identify deficient enzymes  Genetic testing for confirmation Treatment  Supportive care  MPS types I, II, and III have the highest incidence  Enzyme replacement therapy  As of 2021, only four cases of MPS type IX had been reported  Hematopoietic stem cell transplantation  Gene therapy under investigation for MPS types I, II, IIIA, and IV Pathophysiology  Caused by reduced activity of enzymes needed to degrade: o Dermatan sulfate o Heparan sulfate o 2. SPHINGOLIPIDOSES  Group of LSDs caused by deficiencies in enzymes required for sphingolipid degradation Keratan sulfate  Leads to accumulation of phospholipids in tissues o Chondroitin sulfate  Common examples include: o Hyaluronan  Partially degraded substrates accumulate in lysosomes  Leads to severe clinical consequences and shortened survival o Gaucher disease o Niemann-Pick disease PRELIM HEMATOLOGY 2 JANUARY 2026 BMLS 3B Chapter 26: Nonmalignant Leukocyte Disorders A. GAUCHER DISEASE (GD) o Acid phosphatase  Most common lysosomal storage disorder  Autosomal recessive inheritance o Anemia  Caused by deficiency of β-glucocerebrosidase o Thrombocytopenia  Leads to accumulation of glucocerebroside in macrophages  Affected tissues include: o Spleen o Liver o Bone marrow o Bone o Brain (microglia) Genetics  Caused by mutation in GBA gene located at 1q21– q22  Over 400 pathogenic mutations identified  Clinical severity often cannot be predicted by genotype Types  Three types exist  Type I is the most common  Neurologic involvement differentiates the subtypes Gaucher Cells    Bone marrow infiltration causes: Diagnosis  Measurement of β-glucosidase activity  Genetic testing for common mutations including: o N370S o 84GG o IVS2 +1G>A o L444P Complications  Increased risk of hematopoietic malignancies  Most commonly multiple myeloma Treatment  Enzyme replacement therapy  Substrate reduction therapy  HSCT is potentially curative but rarely used due to high mortality  Emerging therapies include gene therapy, genome editing, and chaperone therapy a. PSEUDO-GAUCHER CELLS Enlarged macrophages with:  Seen in conditions with increased cell turnover such as: o Eccentric nuclei o Blue-gray fibrillar cytoplasm o Thalassemia o Wrinkled or onion-skin appearance o Myeloid neoplasms o Acute lymphoblastic leukemia Positive staining with: o Trichrome o Non-Hodgkin lymphoma o Aldehyde fuchsin o Plasma cell neoplasms o PAS PRELIM HEMATOLOGY 2 JANUARY 2026 BMLS 3B Chapter 26: Nonmalignant Leukocyte Disorders  Result from relative enzyme overload rather than true deficiency  Indistinguishable from true Gaucher cells on routine stains  Electron microscopy shows needle-like inclusions instead of tubular structures B. NIEMANN-PICK DISEASE (NP)  Three subtypes: A, B, and C  Less than 5 percent normal enzyme activity  Death usually occurs by 4 years of age b. NP Type B  Non-neuronopathic form  Approximately 10 to 20 percent normal enzyme activity  Presents in childhood or adulthood  Features include: NP TYPES A AND B (Acid Sphingomyelinase Deficiency) o Massive hepatosplenomegaly  Autosomal recessive o Pulmonary insufficiency  Caused by mutation in SMPD1 gene at 11p15.4 o Heart disease  Results in deficiency of acid sphingomyelinase  Leads to accumulation of sphingomyelin in:  o Liver o Spleen o Lungs Over 200 pathogenic mutations identified Bone Marrow Findings  Foam cells  Sea-blue histiocytes  Sea-blue histiocytes also appear in CML, MDS, and lymphoma a. NP Type A  Acute neuronopathic form  Presents in infancy  Features include: o Failure to thrive o Hepatosplenomegaly o Vision problems o Rapid neurodegeneration  No neurocognitive impairment Diagnosis  Enzyme activity measurement in lymphocytes or fibroblasts  Genetic sequencing of SMPD1  Population-specific mutation screening Treatment and Prognosis  Enzyme replacement therapy  Ineffective for neurologic disease in NP type A  Most NP type A patients die within 3 years  Variable prognosis in NP type B  In 2022, FDA approved olipudase alfa as first disease-modifying therapy  Survival impact still unknown c. NIEMANN-PICK TYPE C (NPC)  Rare autosomal recessive disorder  Caused by mutations in: o NPC1 gene in 95 percent of cases o NP2 gene in 5 percent of cases PRELIM HEMATOLOGY 2 JANUARY 2026 BMLS 3B Chapter 26: Nonmalignant Leukocyte Disorders Pathophysiology Epidemiology  Impaired intracellular cholesterol trafficking  Accumulation of unesterified cholesterol in lysosomes Clinical Features  Highly variable presentation  Neurologic and psychiatric symptoms  Visceral organ involvement  Variable age of onset  Prevalence in the United States is approximately 1 in 4,785 individuals. Genetics and Pathophysiology  Caused by a mutation in the lamin B receptor (LBR) gene.  The lamin B receptor is an inner nuclear membrane protein essential for: o Nuclear segmentation o Chromatin organization during leukocyte maturation Diagnosis  First-line screening with serum biomarkers: o Oxysterols o Lyso-SM-509 o Lysosphingomyelin  Genetic testing of NPC1 and NP2 confirms diagnosis  Suspicion index tool aids early recognition Treatment and Prognosis  Most cases are heterozygous, with about 50 percent expression of lamin B receptor. Morphologic Features  Seen mainly in neutrophils, but may also affect other leukocytes.  Classic appearance is bilobed nuclei connected by a thin filament, known as the pince-nez appearance.  Other nuclear shapes include:  No approved treatments as of February 2023 o Round  Treatment is supportive o Ovoid  Substrate reduction therapy may slow neurologic progression o Peanut-shaped  1. PELGER-HUËT ANOMALY (PHA) Definition  All PHA neutrophils show coarse, chunky chromatin regardless of nuclear shape.  Neutrophils are fully mature and function normally. Median age of death is 13 years MORPHOLOGIC ABNORMALITIES OF LEUKOCYTES WITHOUT ASSOCIATED IMMUNE DEFICIENCY   Pelger-Huët anomaly is a benign autosomal dominant disorder characterized by decreased nuclear segmentation of neutrophils and a coarse chromatin pattern. Also known as true or congenital PHA. Clinical Features  Heterozygous individuals are clinically well.  Rare homozygous PHA results in: o Nearly complete absence of nuclear lobulation o Cognitive impairment o Congenital heart defects o Skeletal abnormalities PRELIM HEMATOLOGY 2 JANUARY 2026 BMLS 3B Chapter 26: Nonmalignant Leukocyte Disorders 2. PSEUDO OR ACQUIRED PELGER-HUËT ANOMALY (PPHA) Definition   An acquired morphologic abnormality resembling true PHA.  Seen in various disease states and drug exposures. Etiology    Clinical Significance Linked to loss of the LMNB1 gene on chromosome 5q. DIFFERENCES BETWEEN PELGER-HUET NEUTROPHILS AND IMMATURE GRANULOCYTES 1. Overview  Pelger-Huët (PH) neutrophils are mature neutrophils with abnormal nuclear morphology.  Can appear as round, oval, or peanut-shaped nuclei, which may resemble immature forms (myelocytes, metamyelocytes, band neutrophils).  Important: Do not misclassify PH neutrophils as immature neutrophils to avoid unnecessary tests and misdiagnosis. Commonly associated with: o Myelodysplastic syndromes (MDS) o Acute myeloid leukemia (AML) o Myeloproliferative neoplasms Also associated with: o Autoimmune diseases o Severe bacterial infections o HIV o Tuberculosis o Mycoplasma pneumonia o COVID-19 infection, where severity correlates with the number of PPHA neutrophils Drug Associations  Immunosuppressants  Chemotherapy agents  Valproate  Sulfisoxazole  Fluconazole  Ganciclovir  Hematopoietic growth factors  Ibuprofen In MDS, PPHA neutrophils indicate granulocyte dysplasia and have diagnostic importance. Feature Pelger-Huët Neutrophils Cell size Smaller Immature Neutrophils (myelocytes/metamyelocyt es) Larger Nucleustocytoplas m (N:C) ratio Nuclear shape Lower Higher Bilobed (pincenez), unilobed, or round Darker, coarser, densely clumped (hypercondense d) Mature, nonbasophilic, normal granules (pseudo-PHA in MDS may be hypogranular) Typically banded or round/oval depending on stage Lighter, finer, less condensed Chromati n Cytoplas m Some degree of basophilia, may be less granular PRELIM HEMATOLOGY 2 JANUARY 2026 BMLS 3B Chapter 26: Nonmalignant Leukocyte Disorders 3. Clinical Notes 3. Notes  PH neutrophils are usually incidental findings on automated hematology analyzers or blood smears.  True PHA is mostly benign and discovered incidentally.  Guidelines: Report as segmented neutrophils with a comment about Pelger-Huët anomaly.  PPHA often indicates underlying hematologic disorder.  Misidentification can lead to unnecessary investigations or incorrect treatment.  Careful peripheral smear review and family history are key in differentiation.  Molecular testing can provide a definitive distinction when needed. DIFFERENTIATING BETWEEN PSEUDO- AND TRUE PELGERHUËT NEUTROPHILS 1. Overview  3. NEUTROPHIL HYPERSEGMENTATION Pelger-Huët Anomaly (PHA): Congenital, inherited condition causing abnormal nuclear morphology in neutrophils.  Pseudo-Pelger-Huët Anomaly (PPHA): Acquired condition, often associated with myelodysplastic syndromes (MDS), infections, or drugs.  Important to differentiate to avoid misdiagnosis. 2. Key Differentiating Features Feature Percentage of neutrophils affected Cell lineages involved True PHA > 68% Clinical correlation Usually all WBC lineages (nuclear shape & chromatin) Often positive; examination of relatives shows PH morphology Typically asymptomatic Molecular testing Confirms inherited mutation Family history Pseudo-PHA (PPHA) < 35% Definition  Normal neutrophils contain three to five nuclear lobes.  Hypersegmented neutrophils contain more than five lobes. Clinical Associations  Most commonly seen in megaloblastic anemia.  Neutrophils are often larger than normal.  Also observed in: Restricted to neutrophils Negative May be associated with disease (e.g., MDS) Can help confirm acquired status o Myelodysplastic syndromes as a dysplastic feature o Rare hereditary neutrophil hypersegmentation Hereditary Form  Individuals are asymptomatic.  No associated megaloblastic anemia. PRELIM HEMATOLOGY 2 JANUARY 2026 BMLS 3B Chapter 26: Nonmalignant Leukocyte Disorders 4. ALDER-REILLY ANOMALY (ARA) 5. MAY-HEGGLIN ANOMALY (MHA) Definition Definition  A rare inherited disorder characterized by large, dark-staining metachromatic granules in leukocytes. Morphologic Features  Affects granulocytes and sometimes monocytes and lymphocytes.  Granules are known as Reilly bodies.  Composed of partially digested mucopolysaccharides.  Rare autosomal dominant disorder. Key Features  Variable thrombocytopenia  Giant platelets  Large Döhle body-like inclusions in: Clinical Features o Neutrophils o Eosinophils  Leukocyte function is normal. o Basophils  No immune deficiency. o Monocytes Genetics Differential Diagnosis  Can resemble toxic granulation.  Distinguishing features:  Caused by mutations in the MYH9 gene.  Gene location is chromosome 22q12 to 13.  At least 33 pathogenic mutations identified. o Reilly bodies also present in monocytes and lymphocytes. o Toxic granulation is limited to neutrophils.  Defective production of myosin heavy chain type IIA. o Toxic granulation is often accompanied by:  Leads to abnormal megakaryocyte maturation.  Results in impaired platelet fragmentation and giant platelets. o  Neutrophilia  Left shift  Döhle bodies These findings are absent in Alder-Reilly anomaly. Pathophysiology Inclusion Bodies  Döhle body-like inclusions consist of precipitated myosin heavy chains.  True Döhle bodies consist of rough endoplasmic reticulum. Clinical Features  Most patients are asymptomatic.  Some have mild bleeding tendencies depending on thrombocytopenia severity. PRELIM HEMATOLOGY 2 JANUARY 2026 Chapter 26: Nonmalignant Leukocyte Disorders QUANTITATIVE ABNORMALITIES OF LEUKOCYTES BMLS 3B B. LEUKEMOID REACTION Definition 1. QUANTITATIVE ABNORMALITIES OF NEUTROPHILS  Extreme reactive neutrophilic leukocytosis Normal Neutrophil Values  Lower threshold ranges from 25 to 50 × 10⁹ per liter  Often associated with a left shift  Neutrophils (bands plus segmented forms) normally comprise 50 to 70 percent of circulating WBCs in adults  Adult ANC: approximately 2 to 7 × 10⁹ per liter  Pediatric ANC reference interval: approximately 1.5 to 8.5 × 10⁹ per liter  Infections including bacterial, viral, mycobacterial, treponemal, and COVID-19  Relative percentages in the WBC differential should not be used to define neutrophilia or neutropenia  Nonmyeloid malignancies  Medications such as steroids, lithium, minocycline, and myeloid growth factors  Intoxications  Hemorrhage A. NEUTROPHILIA  Hemolysis Definition  Splenectomy  ANC calculations generally include bands and segmented neutrophils only  Adults: ANC greater than 7.0 × 10⁹ per liter  Children: ANC greater than 8.5 × 10⁹ per liter Causes Key Features  Toxic vacuoles in neutrophils suggest infectious etiology Mechanisms  Catecholamine-induced shift of neutrophils from the marginal pool to the circulating pool  Must be differentiated from chronic myeloid leukemia  Increased bone marrow production   Increased release from bone marrow storage pool Mortality rate in hospitalized patients is approximately 45 percent Peripheral Blood Findings  Presence of immature neutrophils such as metamyelocytes and myelocytes  This is referred to as a left shift C. LEUKOERYTHROBLASTIC REACTION Definition  Presence of immature neutrophils and nucleated red blood cells in peripheral blood Associated Findings  Teardrop red blood cells suggest extramedullary hematopoiesis and myelofibrosis PRELIM HEMATOLOGY 2 JANUARY 2026 Chapter 26: Nonmalignant Leukocyte Disorders Common Causes BMLS 3B b. Drug-Induced Neutropenia  Metastatic cancer  Most common cause of acquired neutropenia  Lymphoma   Leukemia Occurs due to myeloid suppression or immunemediated mechanisms  Primary myelofibrosis  Common with cancer therapies  Occasionally seen in hemolysis, infections, and hemorrhage  Mortality rate associated with cancer therapy– related neutropenia is approximately 12.5 percent  Nonchemotherapy drug-induced severe neutropenia mortality is approximately 5 percent  Annual incidence in the United States is 2.3 to 15.4 cases per million  Overall mortality rate ranges from 10 to 16 percent D. NEUTROPENIA Definition  Absolute neutrophil count less than 1.5 × 10⁹ per liter Severity  Increased infection risk below 1.5 × 10⁹ per liter  Severe neutropenia defined as less than 0.5 × 10⁹ per liter  Agranulocytosis defined as less than 0.1 × 10⁹ per liter c. NEONATAL ALLOIMMUNE NEUTROPENIA Mechanism  Maternal IgG crosses placenta  Antibodies target paternal human neutrophil antigens on fetal neutrophils  Antibody-coated neutrophils are cleared by the reticuloendothelial system Mechanisms 1. Increased destruction or removal of neutrophils 2. Decreased production or ineffective hematopoiesis 3. Decreased circulating pool relative to marginal pool 4. Combination of mechanisms Key Features  ANC often less than 0.5 × 10⁹ per liter  Occurs within the first week of life  Most commonly associated antigens are HNA-1 and HNA-3 a. ACQUIRED NEUTROPENIA  Most common form of neutropenia   Causes include infections, autoimmune disorders, nutritional deficiencies, medications, and malignancies Incidence in the United States in 2021 was 0.9 percent  Infections are usually mild  ANC normalizes within 6 months PRELIM HEMATOLOGY 2 JANUARY 2026 Chapter 26: Nonmalignant Leukocyte Disorders d. AUTOIMMUNE NEUTROPENIA (AIN)  Autoimmune disorders Definition  Hematopoietic neoplasms  ANC below age-specific reference interval  Solid tumors  Presence of IgG autoantibodies against human neutrophil antigens  Primary eosinophilic disorders i. Primary AIN  Occurs in approximately 1 per 100,000 children under 10 years  Onset at 7 to 9 months  Usually mild infections  Self-limiting  Recovery by 4 to 5 years BMLS 3B 3. QUANTITATIVE ABNORMALITIES OF BASOPHILS a. Basophilia  Defined as absolute basophil count greater than 0.10 × 10⁹ per liter Causes  Myeloproliferative neoplasms, especially chronic myeloid leukemia ii. Secondary AIN  More common in adults  Acute myeloid leukemia with t(6;9)  Associated with autoimmune diseases, malignancies, infections, transplant, and medications  Therapy-related acute leukemia and myelodysplastic syndromes  Immunologic mechanisms include immune complexes, haptens, autoantibodies, and T-cell toxicity  Acute basophilic leukemia  Atopic disorders  Chronic iron deficiency 2. QUANTITATIVE ABNORMALITIES OF EOSINOPHILS  Hodgkin lymphoma Regulation  Viral infections such as smallpox and chickenpox  Controlled by GM-CSF, IL-3, and IL-5  IL-5 is the primary regulator of eosinophil release into circulation A. Eosinophilia  Defined as absolute eosinophil count greater than 0.4 × 10⁹ per liter Causes  Parasitic infections, especially helminths  Allergic disorders such as asthma and atopic dermatitis  Drug hypersensitivity Laboratory Issues  Automated analyzers may falsely increase basophil counts  Pseudobasophilia has been reported in dengue fever  Basophils may be undercounted in chronic myeloid leukemia  There is reduced confidence in automated basophil differentials PRELIM HEMATOLOGY 2 JANUARY 2026 BMLS 3B Chapter 26: Nonmalignant Leukocyte Disorders 4. QUANTITATIVE ABNORMALITIES OF MONOCYTES A. Monocytosis SECONDARY MORPHOLOGIC CHANGES IN LEUKOCYTES 1.. STORAGE ARTIFACTS IN LEUKOCYTES  Defined as absolute monocyte count greater than 1.0 × 10⁹ per liter  Storage artifacts are in vitro morphologic changes that occur in blood cells after specimen collection.  Seen in infections, inflammation, immune disorders, tissue repair  These artifacts affect leukocytes, red blood cells, and platelets.  Often first sign of marrow recovery   Seen in cyclic neutropenia during neutropenic phases Changes may be observed as early as 2 hours after collection when blood is stored in EDTA.  The Clinical Laboratory Standards Institute (CLSI) recommends that blood films be prepared within 4 hours of collection. B. Monocytopenia  Defined as absolute monocyte count less than 0.2 × 10⁹ per liter   Commonly associated with aplastic anemia and myelosuppressive therapy Morphologic changes seen after 4 hours may mimic true pathologic abnormalities.   Seen with steroid use, hemodialysis, sepsis If reported incorrectly, these artifacts may be misinterpreted as clinically significant findings.  Associated with EBV infection  Profound monocytopenia is characteristic of hairy cell leukemia and GATA2 mutation–related neoplasms Common Storage Artifacts Discussed  Autophagic vacuoles  Pyknotic and apoptotic neutrophils 2. SECONDARY CHANGES IN NEUTROPHILS AND MONOCYTES 5. QUANTITATIVE ABNORMALITIES OF LYMPHOCYTES  Physiologic responses to infection, inflammation, stress, trauma, burns, or administration of G-CSF or GM-CSF usually cause neutrophilia. A. Lymphocytosis  Adults: greater than 5.0 × 10⁹ per liter   Children aged 2 weeks to 9 years: greater than 10.0 × 10⁹ per liter A left shift may be present but is not always observed.  The severity of infection or inflammation influences the ANC and the release of immature neutrophils.  Reactive neutrophil morphologic changes include:  Newborns: greater than 5.0 × 10⁹ per liter  Usually associated with reactive or malignant morphology B. Lymphopenia  Children: less than 2.0 × 10⁹ per liter  Adults: less than 1.0 × 10⁹ per liter  Causes may be inherited or acquired  o Toxic granulation o Döhle bodies o Toxic vacuolation These changes are mediated by cytokines, especially G-CSF. PRELIM HEMATOLOGY 2 JANUARY 2026 BMLS 3B Chapter 26: Nonmalignant Leukocyte Disorders A. TOXIC GRANULATION  Toxic granules are dark, coarse, and prominent granules seen in band and segmented neutrophils.  Cancer  G-CSF administration   They contain enzymes normally found in primary and secondary granules.  Toxic granules contain increased acid mucosubstance, which enhances bactericidal activity.  There is a positive correlation between toxic granulation and elevated C-reactive protein levels.  C. NEUTROPHIL VACUOLATION a. Toxic Vacuoles  Seen less frequently than toxic granulation or Döhle bodies.  Present in neutrophils with toxic granulation and or Döhle bodies.  Indicate active phagocytosis.  More closely associated with infection.  Vacuoles may be up to 6 micrometers in diameter.  May contain microorganisms in rare cases.  Vacuoles may coalesce and distort cell shape. Seen in: o Infections o Inflammation o Pregnancy o Patients receiving G-CSF  Grading toxic granulation is difficult due to irregular distribution.  Toxic granulation may resemble Alder-Reilly bodies, but AR bodies are also seen in other leukocytes. Similar inclusions appear in May-Hegglin anomaly, but in that disorder they are also seen in eosinophils, basophils, and monocytes. b. Autophagic Vacuoles B. DÖHLE BODIES  Döhle bodies are pale blue-gray cytoplasmic inclusions.  They consist of denatured ribosomal RNA or rough endoplasmic reticulum remnants.  Usually found in band and segmented neutrophils.  Often appear together with toxic granulation.  Size ranges from 1 to 5 micrometers.  Usually located near the cell membrane. Associated Conditions  Represent a cellular degradation process.  Vacuoles are approximately 2 micrometers in diameter.  More widely distributed in cytoplasm than toxic vacuoles.  Not associated with toxic granulation or Döhle bodies.  Seen during cell death and specimen processing delays.  Also observed in: o Hypoxia  Severe infections o Starvation  Burns o Alcohol poisoning  Trauma o Radiation exposure  Pregnancy o VEXAS syndrome, described in 2020 PRELIM HEMATOLOGY 2 JANUARY 2026 BMLS 3B Chapter 26: Nonmalignant Leukocyte Disorders D. PYKNOSIS AND APOPTOSIS IN NEUTROPHILS A. Pyknotic Nuclei  Indicate imminent cell death.  Chromatin is dense and dark.  Nuclear filaments are still visible. B. Apoptotic Nuclei B) Human Monocytic Ehrlichiosis (HME)  Caused by Ehrlichia chaffeensis or Ehrlichia ewingii.  Morulae seen within monocytes.  Primary reservoir is the white-tailed deer. Clinical and Laboratory Findings  Fever, chills, malaise, headache, myalgia.  Leukopenia due to neutropenia or lymphopenia.  Found in dead neutrophils.  Thrombocytopenia.  Rounded, dense nuclear fragments.  Elevated liver enzymes.  No visible chromatin pattern or filaments.   Can resemble nucleated red blood cells. Nonhemolytic anemia in about 50 percent of patients.  Presence of cytoplasmic granules distinguishes apoptotic neutrophils from nucleated RBCs.  Morulae detected in up to 80 percent of HGA cases and 5 percent of HME cases.  Often associated with delayed smear preparation.  Diagnosis confirmed by PCR.  Treatment with doxycycline is effective. E. INTRACELLULAR ORGANISMS IN NEUTROPHILS AND MONOCYTES A. Bacteria and Fungal organism  Rare finding.  Seen in disseminated infections.  Generally associated with poor prognosis.  May also be observed in asymptomatic patients with indwelling catheters or recent surgical or dental procedures. TICKBORNE INTRACELLULAR BACTERIA A) Human Granulocytic Anaplasmosis (HGA) F. GREEN-BLUE INCLUSIONS IN NEUTROPHILS AND MONOCYTES  Also called critical blue-green inclusions or crystals of death.  Rarely reported before 2009.  Seen in neutrophils and occasionally monocytes.  Appear as green or blue-green refractile cytoplasmic bodies.  Thought to contain lipofuscin from necrotic liver cells.  Associated with: o Acute liver failure o Multiorgan failure  Caused by Anaplasma phagocytophilum. o Sepsis  Organisms form morulae within neutrophils. o Lactic acidosis  Primary reservoir is the white-footed mouse. o COVID-19 PRELIM HEMATOLOGY 2 JANUARY 2026 BMLS 3B Chapter 26: Nonmalignant Leukocyte Disorders o  Yellow fever Often indicate impending death. G. REACTIVE MONOCYTES  Seen in infections, including COVID-19.  Observed during marrow recovery and GM-CSF therapy.  Morphologic features include:  o Immature chromatin o Small nucleoli o Increased nuclear to cytoplasmic ratio o Deepened cytoplasmic basophilia o Increased vacuolation o Distinct granulation B. Hypogranular Basophils  Basophil granules are water soluble and may wash out during staining.  Cells may appear pale with residual pink staining.  Hypogranular basophils may also be seen in myeloid neoplasms. 4. LYMPHOCYTES A. Reactive Lymphocytes  Previously known by many terms including Downey cells and atypical lymphocytes.  The International Committee for Standardization in Hematology (ICSH) recommends: Differentiation from malignant monocytes is difficult but critical.  3. EOSINOPHILS AND BASOPHILS A. Ruptured Eosinophils   Eosinophils are fragile and may rupture during smear preparation. Damaged eosinophils should still be counted as eosinophils.  Failure to do so leads to falsely low eosinophil counts.  Hypogranular or mixed granulation eosinophils are associated with myeloid neoplasms. o Reactive lymphocyte for benign causes o Abnormal lymphocyte for malignant or clonal causes Reactive lymphocytes greater than 5 percent are usually associated with absolute lymphocytosis. Morphologic Features  Larger size compared to resting lymphocytes.  Variable nuclear shape and chromatin pattern.  Possible visible nucleoli.  Increased basophilic cytoplasm.  Cytoplasm may indent surrounding red blood cells.  Heterogeneous appearance. Plasmacytoid Lymphocytes  A subtype of reactive lymphocyte.  Share features with plasma cells.  Seen in small numbers in benign conditions.  Large numbers or uniform populations suggest lymphoid neoplasm PRELIM HEMATOLOGY 2 JANUARY 2026 Chapter 26: Nonmalignant Leukocyte Disorders INFECTIOUS MONONUCLEOSIS (IM) BMLS 3B III. CLINICAL FEATURES Common Symptoms: I. ETIOLOGY  Sore throat (± tonsillar exudate)  Caused by Epstein-Barr Virus (EBV).  Dysphagia  Most common in 15- to 24-year-olds.  Fever and chills  Asymptomatic EBV infections are frequent in young children.  Posterior cervical lymphadenopathy   Up to 95% of adults are seropositive, but symptomatic IM is uncommon. Fatigue  Loss of appetite  EBV is also associated with:  Headache  Splenomegaly (>50% of patients) o Lymphoid neoplasms and other cancers o Post-transplant lymphoproliferative disease o Chronic fatigue syndrome  Abdominal pain, nausea, vomiting o Multiple sclerosis  Hepatomegaly with abnormal liver function tests o Autoimmune diseases  Rash, petechiae o Vitamin D deficiency  Eyelid edema Additional Symptoms (up to 20% of cases): Rare Complications: II. INCUBATION AND PATHOPHYSIOLOGY  Aplastic anemia  Incubation period: 3 to 7 weeks  Hemolytic anemia  EBV primarily infects B lymphocytes:  Thrombocytopenia  Disseminated intravascular coagulation (DIC)  Neurologic complications o  EBV also infects oropharyngeal epithelial cells, mechanism unclear. o  Via viral glycoprotein 350/220 binding to CD21 (C3d receptor) and CD35 (CR1). Glycoprotein BMRF2 may facilitate entry via β1, α5, and α3 integrins. Immune response: o Activation of NK cells, CD4+ T cells, and CD8+ cytotoxic T cells (EBV-CTLs) o Reactive lymphocytes seen in peripheral blood are mainly activated CD8+ T cells. PRELIM HEMATOLOGY 2 JANUARY 2026 Chapter 26: Nonmalignant Leukocyte Disorders IV. LABORATORY FINDINGS Complete Blood Count (CBC):  Absolute lymphocytosis  10–50% or more reactive (atypical) lymphocytes  Peripheral blood smear: o Pleomorphic reactive lymphocytes o Classic Downey type II cells:  Larger cells with abundant, basophilic cytoplasm  Cytoplasm “hugs” surrounding RBCs (ballerina-skirt appearance) V. DIAGNOSTIC TESTS EBV-specific Antibody Testing (for heterophile-negative patients):  Viral Capsid Antigen (VCA) IgM/IgG  EBV Nuclear Antigen (EBNA) IgG  Higher sensitivity and specificity  More expensive and longer turnaround Differential Diagnosis:  Detects IgM heterophile antibodies that cross-react with mammalian RBCs  Sensitivity: 87%  Specificity: 91%  Limitations: o 40% false negatives in children <5 years o 25% of newly infected older adults may test negative o False positives may occur in:  Other infections  Autoimmune diseases  Cancer Cytomegalovirus (CMV) mononucleosis syndrome may mimic EBV IM. VI. SUMMARY POINTS  EBV infects B cells and sometimes epithelial cells.  Immune response is predominantly CD8+ cytotoxic T cells.  Clinical triad: Fever, sore throat, lymphadenopathy.  Most patients are self-limited.  Diagnosis: CBC with reactive lymphocytes + heterophile antibody test; EBV serology if heterophile-negative. Rapid Heterophile Antibody Test:  BMLS 3B HEMATOLOGY 2 Chapter 26: Nonmalignant Leukocyte Disorders OUTLINE Primary Immunodeficiency Disorders/Inborn Errors of Immunity  Severe Combined Immune Defeciency  Wiskott-Aldrich Syndrome  22q11.2 Deletion Syndrome  Bruton Tyrosine Kinase Defeciency  Chediak-Higashi Syndrome  Congenital Defects of Phagocyte Number and/or Function Lysosomal Storage Disorders  Mucopolysaccharidoses  Sphingolipidoses Morphologic Abnormalities of Leukocytes Without  Associated Immune De ciency  Pelger-Huet Anomaly  Pseudo– or Acquired Pelger-Huet Anomaly  Neutrophil Hypersegmentation  Alder-Reilly Anomaly  May-Hegglin Anomaly Quantitative Abnormalities of Leukocytes  Quantitative Abnormalities of Neutrophils  Quantitative Abnormalities of Eosinophils  Quantitative Abnormalities of Basophils  Quantitative Abnormalities of Monocytes  Quantitative Abnormalities of Lymphocytes Secondary Morphologic Changes in Leukocytes  Storage Artifacts in Leukocytes  Secondary Changes in Neutrophils and Monocytes  Eosinophils and Basophils  Lymphocytes Infectious Mononucleosis PRELIM JANUARY 2026 BMLS 3B