Endocrinology of Pituitary

Growth hormone Chemistry and synthesis Function GH or somatotropin Its larger precursor peptide polypeptide hormone has no physiologic significance Promotion of growth. Most of the growth-promoting effects are mediated by insulin-like growth factor 1. GH, via IGF-I, increases protein synthesis by: 1. enhancing amino acid uptake 2. Directly accelerating the transcription and translation of mRNA. decrease protein catabolism by : Mobilizing fat as a more efficient fuel source: it directly causes the release of fatty acids from adipose tissue and enhances their conversion to acetyl-CoA, from which energy is derived. This protein-sparing effect is an important mechanism by which GH promotes growth and development GH also affects carbohydrate metabolism. )) GH↑ → resistance of insulin ↑ )) In excess, it decreases carbohydrate utilization and impairs glucose uptake into cells. This GH-induced insulin resistance appears to be due to a post-receptor impairment in insulin action. These events result in glucose intolerance and secondary hyper-insulinism Secretion regulation Growth Hormone Has Many Other Effects On The Body: 1. increasing height in children and adolescents 2. Increases calcium retention 3. Increases muscle mass through sarcomere hypertrophy 4. Promotes lipolysis 5. Increases protein synthesis 6. Stimulates the growth of all internal organs excluding the brain 7. Reduces liver uptake of glucose 8. Promotes gluconeogenesis in the liver 9. Contributes to the maintenance and function of pancreatic islets 10. Stimulates the immune system The secretion of GH is predominantly mediated by two hypothalamic hormones : GHRH and somatostatin(GH-inhibiting hormone) hypothalamus neural, metabolic, and hormonal factors  Metabolic factors affecting GH secretion include all fuel substrates: Carbohydrate, protein, and fat. {{ protein , amino acid → ↑ GH }} Stimulators of growth hormone (GH) secretion include: 1. GHRH (somatocrinin) through binding to the (GHRHR) 2. Sex hormones Increased androgen secretion during puberty (in males from testes and in females from adrenal cortex) 3. Hypoglycemia and arginine {{ ↓glu. → GH  }} 4. Deep sleep 5. Fasting stimulates GH secretion, possibly as a means of mobilizing fat as an energy source and preventing protein loss. {{ Fasting → glu.  →GH ↑ → lipolysis ↑ → insulin  }} 6. Vigorous exercise 1. 2. 3. 4. Inhibitors of GH secretion include: GHIH (somatostatin) from the periventricular nucleus [32] circulating concentrations of GH and IGF-1 Hyperglycemia Glucocorticoids (cortisol) Disease state Excess GH Hypersecretion causes gigantism in children or acromegaly in adults. The most common disease of GH excess is a pituitary tumor composed of somatotroph cells of the anterior pituitary. Prolonged GH excess thickens the bones of the jaw, fingers and toes, resulting heaviness of the jaw and increased size of digits, referred to as acromegaly. Accompanying problems can include : ✓ Sweating, pressure on nerves, muscle weakness, ✓ Excess sex hormone-binding globulin (SHBG) ✓ Insulin resistance or even a rare form of type 2 diabetes, and reduced sexual function. Treatment : ✓ Surgical removal tumors. ✓ Radiation. ✓ GH antagonist. ✓ somatostatin agonist \ dopamine agonist :; used to block GH secretion Acromegaly Acromegaly is almost exclusively caused by a GH-secreting pituitary tumour. Patients have often had acromegaly for many years before the diagnosis is considered. he increased detection of accompanying pituitary tumours can lead to early diagnosis if appropriate tests are performed. Untreated acromegaly can lead to disfiguring features and premature death, predominantly from cardiovascular disease Symptoms: Diagnosis: Facial change clinical feature Growth hand and feet GH ↑ \ IGF-1 ↑ Headache OGTT no suppression Sweeting MRI pituitary tumor carpal tunnel syndrome (pressure on nerves) snoring \sleep apnoea lethargy Deficiency of GH Hyposecretion of hGH causes dwarfism in children. The effects of growth hormone (GH) deficiency vary depending on the age at which they occur. Manifestations in children: ✓ growth failure ✓ short stature ✓ delayed sexual maturity manifestations In adults: ( rare) ✓ increased osteoclast activity ✓ Relative increase in fat mass. {{ GH → lipolysis  → accumulation of fat }} ✓ Relative decrease in muscle mass. ✓ Decreased energy and quality of life. Laron syndrome autosomal recessive disorder characterized by an Diagnosis: insensitivity to growth hormone (GH) ((resistance)) through biochemical analyses: Caused by a mutant growth hormone receptor. basal GH levels are abnormally increased, It causes : IGF-1 is low ✓ short stature When a GHRH test is performed, ✓ Increased sensitivity to insulin which means IGF-1 fails to increase. that diabetes mellitus type 2 is less likely to develop. GHBP (GH- binding protein) Treated with injections of recombinant IGF-1. low → mutations in the extracellular domain of the GH receptor normal → mutations in the intracellular domain Genetic tests : etiological diagnosis. Lab Test (GH) The early morning GH concentration in fasting unstressed adults is less than 2 ng/mL (90 pmol/L). There are no significant sex differences. Transition in circulation by → bound to specific GH-binding proteins (GHBPs) ▪ reduce oscillations in GH levels ( More stabilization ) ▪ ↑ half life ▪  metabolism Useful For Diagnosis of acromegaly GH only not enough to diagnosis, if use it → must perform result from glucose suppression test.  GH → normal Still high ↑ → tumor Diagnosis of human growth hormone deficiency when interpreted in conjunction with results from growth hormone stimulation test ↑ GH → normal Still low  → deficiency This test is not intended for use as a screen for acromegaly. This test has limited value in assessing growth hormone secretion in normal children. Reference Values Lab Test Cautions Lab Test Interpretati on Specimen Patient Preparation Reject hGH levels in normal and diseased populations overlap hGH suppression and stimulation tests are needed to evaluate conditions of hGH excess and deficiency; random hGH levels are inadequate. Reference Values Adults Males: 0.01-0.97 ng/mL \\\ Females: 0.01-3.61 ng/mL Elevated levels of human growth hormone (hGH ) indicate the possibility of gigantism or acromegaly, but must be confirmed with stimulation and suppression testing. Growth hormone is secreted in surges; single measurements are of limited diagnostic value. Acromegaly: Deficiency: For suppression testing, For stimulation tests Normal subjects have (hGH) concentration below 0.3 A normal response have a peak hGH ng/mL after ingestion of a 75-gram glucose dose. concentration above 5 ng/mL in children and Patients with acromegaly fail to show normal suppression above 4 ng/mL in adults Serum The recommended test for assessing growth hormone secretion in normal children is IGF1I / Insulin-Like Growth Factor 1, Serum. The preferred test for acromegaly screening is IGF1 / Insulin-Like Growth Factor 1, Serum Fasting, 8 hours Glu.  → GH ↑ → IGF-1 ↑ Gross hemolysis Reject Gross Lipemia OK Method Description Immunoenzymatic ("sandwich") assay. Dynamic Lab Test Doubt to decrease → stimulation test. Insulin-Induced Hypoglycemia Give insulin → glu.  → GH ↑ >5 ng\ml ( normal ) Give insulin → glu.  → GH  ( deficiency ) GHRH-Arginine Test Give GHRH combined with infusion of arginine → GH ↑ >10-15 ( normal ) Give GHRH combined with infusion of arginine → GH  ( deficiency ) Glucagon Stimulation Test Give glucagon → GH ↑ > 3ng\ml ( normal ) Give glucagon → GH  ( deficiency ) GH Doubt to increase → suppression test Oral glu. Tolerance Give glu. → GH  < 1μg/L ( normal ) Give glu. → GH ↑ ( acromegaly) IGF-1 levels are elevated in acromegaly, reflecting increased GH activity. Prolactin Chemistry and synthesis Function PRL is a 198-amino-acid polypeptide hormone synthesized and secreted from the lactotropes of the anterior pituitary. stimulates lactation in the postpartum period. The major chemical controlling prolactin secretion is dopamine, which inhibits prolactin secretion from the pituitary. During pregnancy, : PRL secretion increases and, in concert with many other hormones (estrogen, progesterone, insulin, and cortisol), promotes additional breast development in preparation for milk production. estrogen enhances breast development but blunts the effect of PRL on lactation; the decrease in both estrogen and progesterone after parturition allows initiation of lactation Although basal PRL secretion falls in the postpartum period, lactation is maintained by persistent breast suckling. In normal individuals, prolactin concentrations increase in response to physiologic stimuli such as sleep, stress, exercise, sexual intercourse, and hypoglycemia, and concentrations are also elevated during: pregnancy, lactation, postpartum, and in a newborn infant. regulation ❖ The hypothalamic control of PRL secretion is predominantly inhibitory, ❖ and dopamine is the most important inhibitory factor. ❖ Prolactin follows diurnal and ovulatory cycles. ❖ Prolactin levels peak during REM sleep and in the early morning. ❖ The hormone is cleared by the liver (75%) and the kidney (25%), ❖ and its half-time of disappearance from plasma is about 25 to 50 minutes. ❖ During pregnancy : High circulating concentrations of estrogen and progesterone increase prolactin levels by 10- to 20-fold. Estrogen and progesterone inhibit the stimulatory effects of prolactin on milk production. The abrupt drop of estrogen and progesterone levels following delivery allow prolactin—which temporarily remains high—to induce lactation. ❖ The sucking activates mechanoreceptors in and around the nipple→ These signals are carried by nerve fibers through the spinal cord to the hypothalamus→ where changes in the electrical activity of neurons that regulate the pituitary gland → increase prolactin secretion. ❖ The suckling stimulus also triggers the release of oxytocin from the posterior pituitary gland, → which triggers milk let-down: Prolactin controls milk production (lactogenesis) but not the milk-ejection reflex; the rise in prolactin fills the breast with milk in preparation for the next feed. ❖ In usual circumstances, in the absence of galactorrhea, lactation ceases within one or two weeks following the end of breastfeeding. receptor Prolactin is water soluble ,so the receptor present in surface of cell. Receptors are present in the mammillary glands, ovaries, pituitary glands, heart, lung, thymus, spleen, liver, pancreas, kidney, adrenal gland, uterus, skeletal muscle, skin and areas of the central nervous system. When prolactin binds to the receptor, → it causes it to dimerize with another prolactin receptor. ➔ This results in the activation of Janus kinase 2, a tyrosine kinase that initiates the JAK-STAT pathway. Disease state Hyperprolactinemia most common hypothalamic-pituitary disorder. Causes; prolactin-secreting pituitary adenoma (prolactinoma) functional and organic disease of the hypothalamus primary hypothyroidism compression of the pituitary stalk clinical features : loss of libido, galactorrhea, oligo-menorrhea or amenorrhea, and infertility in premenopausal females and loss of libido, impotence, infertility, and hypogonadism in males Postmenopausal and premenopausal women, as well as men, can also suffer from decreased muscle mass and osteoporosis Prolactinomas may rarely present in childhood or adolescence. In girls, disturbances in menstrual function and galactorrhea may be seen, whereas in boys, delayed pubertal development and hypogonadism are often present. Hypoprolactinemia PRL secretion by the pituitary is the most resistant to local damage, Causes: hypopituitarism, excessive dopaminergic action in the tuberoinfundibular pathway and ingestion of D2 receptor agonists such as bromocriptine. DA↑ → PRL ↓ clinical features : ovarian dysfunction in women, and arteriogenic erectile dysfunction, premature ejaculation, hypofunction of seminal vesicles hypoandrogenism in men oligozoospermia, asthenospermia Lab test Useful For Aiding in evaluation of pituitary tumors, amenorrhea, galactorrhea, infertility, and hypogonadism Monitoring therapy of prolactin-producing tumors Diagnostic use Prolactin levels may be checked as part of a sex hormone workup, as elevated prolactin secretion can suppress the secretion of FSH and GnRH, leading to hypogonadism and sometimes causing erectile dysfunction. Prolactin levels may be of some use in distinguishing epileptic seizures from psychogenic non-epileptic seizures. The serum prolactin level usually rises following an epileptic seizure Method Name Electrochemiluminescence Immunoassay Specimen Serum Reference Values Males: 4.0-15.2 ng/mL Females ( non-pregnant ): 4.8-23.3 ng/mL Patient Preparation: For 12 hours before specimen collection do not take multivitamins or dietary supplements containing biotin (vitamin B7), Interpretation: serum prolactin concentrations parallel tumor size in patients with prolactinomas. Macroadenomas (>10 mm in diameter) are typically associated with serum prolactin concentrations above 250 ng/mL concentration above 500 ng/mL is diagnostic of a macroprolactinoma. Moderately increased concentrations of serum prolactin are not a reliable guide for determining whether a prolactinproducing pituitary adenoma is present. After initiation of medical therapy of prolactinomas, prolactin levels should decrease substantially in most patients Failure to suppress prolactin levels may indicate tumors resistant to the usual central-acting dopamine agonist therapies; In patients where a discrepancy between pituitary tumor size and prolactin elevation is observed, a test for false-low serum prolactin (hook effect) should be performed by serial dilution. In patients with asymptomatic hyperprolactinemia, assessment for macroprolactin (prolactin bound to immunoglobulin) is suggested. Caution: Serum prolactin measurements are not recommended during pregnancy in patients with prolactinomas For assays employing antibodies, the possibility exists for interference by human antianimal antibodies (ie, heterophile antibodies) in the patient sample This may falsely elevate or falsely decrease the results. A full drug history is required because dopamine antagonists cause an elevation in prolactin. Profound hypothyroidism can cause hyperprolactinaemia by TRH-driven prolactin secretion. In large pituitary tumours, a prolactin level >5000 iU/L suggests a macroprolactinoma rather than a nonfunctioning adenoma Thyroid Overview Thyroid hormones regulate a number of developmental, metabolic, and neural activities throughout the body. The 2 main hormones secreted by the thyroid gland are: thyroxine, (T4), and triiodothyronine (T3). T3 production in the thyroid gland constitutes approximately 20% of the total T3 in circulation ; the rest is generated by the conversion (de-iodination) of T4 to T3 80% Circulating levels of T4 are much greater than T3 levels, T3 is biologically the most metabolically active hormone (3-4 times more potent than T4) although its effect is briefer due to its shorter half-life compared to T4. In circulation : ✓ bound to carrier proteins (e.g., thyroid-binding globulin: TBG, pre-albumin, and albumin) ✓ Small fraction circulates unbound (free) & only the free forms are metabolically active. In hyperthyroidism, both T4 and T3 levels are usually elevated, but in a small subset of hyperthyroid patients only T3 is elevated (T3 toxicosis). In hypothyroidism T4 and T3 levels are decreased. T3 levels are frequently low in sick or hospitalized euthyroid patients Histology Present in neck region , as form two loops Thyroid tissue is made up of colloid fluid that contains the iodinated thyroglobulin (prohormone) that bind with T3/T4 Cell that secret th. hormone is → follicular cell ( thyrocyte / thyroid epithelial cell ) Thyroglobulin is the large molecule from which thyroxine is made and stored in colloid , it synthesised by the surrounding follicular cells . Thyroglobulin will break down to give T3/T4. The thyroid is also made up of neuroendocrine cells (parafollicular or C cells), which are situated between the follicular cells, and secrete calcitonin, Calcitonin is relevant clinically as a biomarker for medullary thyroid cancer (a form of thyroid carcinoma which originates from the parafollicular cells (C cells)). calcitonin parafollicular thyroid Lilas synthesis TSH bind with receptor on surface of cell → stimulate endocytosis colloid → The endocytosed vesicles fuse with the lysosomes of the follicular cell → The lysosomal enzymes cleave the T4 from the iodinated thyroglobulin → then into blood vessels. Function T3 increases : ✓ the basal metabolic rate : minimal caloric requirement needed to sustain life by increases the production of the Na+/K+ -ATPase increases the turnover(synthesis and degradation) of different endogenous macromolecules ✓ body's oxygen ✓ energy consumption. Protein: stimulates the Glucose: Lipids: production of RNA Polymerase I ↑ rate of glycogen breakdown and breakdown of cholesterol and and II → protein synthesis ↑ glucose synthesis in gluconeogenesis increases the number of LDL receptors → lipolysis ↑ Heart: Metabolic rate ↑ →O2 need↑ → force of contraction ↑ → output ↑ →systolic↑/diastolic ↓ Receptor & metabolism Development: developing embryo and infants It affects the lungs & growth of the central nervous system. It stimulates the production of : myelin, neurotransmitters, and the growth of axons. It is also important in the linear growth of bones Th. hormones are lipid soluble → receptor will found inside the cell . two main types of thyroid receptor (TRα and TRβ), with variably expressed in different tissues. de-iodinase enzymes: contribute to activation and inactivation of the initially released hormone precursor T4 (thyroxine) into T3 (triiodothyronine) Disease state Hyperthyroidism Thyrotoxicosis: common condition. It most commonly affects young women but can also develop in men and occur at any age. Symptoms: increased activation of the sympathetic nervous system Weight loss, insomnia and irritability, anxiety, heat intolerance. Hyperthyroidism is less common in children than adults. Patients can present with classic symptoms, or with accelerated growth and behavioural disturbance. Primary Secondary Increased circulating T3 and T4, and suppressed TSH due to Increased circulating T3 and T4, with normal or negative feedback. high TSH T3 toxicosis Elevated fT3 alone with suppressed TSH subclinical hyperthyroidism normal fT4/fT3 and suppressed TSH (autonomous thyroid activity) This is often due to the presence of nodular thyroid disease. TSH normal range Patients may not be symptomatic, but are at risk of the same long-term complications as hyperthyroidism especially if the TSH is completely unmeasurable. Treatment is indicated to control symptoms Hyperthyroidism and pregnancy Hyperemesis gravidarum ✓ Common in pregnant woman , with complication such as :: vomiting & nausea ✓ Result because → β-HCG high , TSH has a similar molecular structure to β-HCG → ✓ hyperemesis of pregnancy can be associated with mild biochemical hyperthyroidism ✓ This usually resolves spontaneously in the second trimester of pregnancy Graves’ disease in pregnancy Pregnancy usually has a beneficial effect on autoimmune disease, including Graves’ disease, such that the dose of antithyroid medication can usually be reduced or even stopped. Placental transfer of TSH receptor stimulating antibodies can affect the fetus → increase thyroid Hormone → case tachycardia, goitre or growth restriction, which are signs of fetal hyperthyroidism. Breastfeeding ✓ is safe on anti-thyroid medication, as long as doses are not excessive ✓ Hyperthyroidism often becomes worse after delivery, because the immunosuppressive effect of pregnancy is removed, demanding an appropriate dosage increase in therapy Elevated fT4 with unsuppressed TSH A high fT4 with a suppressed TSH is the norm in hyperthyroidism It is unusual in clinical practice to see a high fT4 with non-suppressed TSH Cause : assay interference, TSHoma and thyroid hormone resistance TSHoma TSH-secreting pituitary tumour which drives fT3 and fT4 production from the thyroid TRH TSH Patients present with symptoms of hyperthyroidism, or mass effect from the pituitary tumour if it is a macroadenoma. Treatment: somatostatin analogues are effective in achieving biochemical control. Thyroid hormone resistance high fT3/fT4 and non-suppressed TSH caused by :: an inactivating mutation in the thyroid hormone receptor β (TR-β ) gene A diagnosis can be confirmed by genetic testing Thyroiditis inflammation of the thyroid gland caused by:: viral infection, medication (commonly amiodarone) or follows childbirth hypo hyper Cases : Graves’ disease autoimmune thyroid disease results from the production of Ab against own cells → can stimulate TSH receptor (( called TSH receptor stimulating Ab)) It typically affects young women and usually follows a relapsing–remitting course. Symptoms: Thyroid eye disease, skin changes characterized by pre-tibial myxoedema as well as nail changes similar to clubbing. These are a result of cross-reactivity with TSH receptors in the back of the orbit and skin. Diagnosis : Thyroid antibodies: Thyroid peroxidase antibodies (TPO) :: are non-specific markers of autoimmune thyroid disease. TSH receptor stimulating antibodies :: are more specific and can be helpful in particular clinical situations such as pregnancy, in addition to supporting a clinical diagnosis of Graves’ disease Nodular thyroid disease second most common cause of hyperthyroidism presents at an older age than Graves’ disease caused by autonomous secretion of T3 and/or T4 from: solitary toxic nodule more commonly, numerous nodules situated within a multinodular goitre (‫)تضخم‬ Symptoms: Enlargement of the thyroid gland. Hypothyroidism Clinical features weight gain, cold intolerance, fatigue, constipation, Bradycardia, with thickening of the skin and puffiness around the eyes (myxoedema). Primary hypothyroidism: Causes : disease, characterised by: the presence of thyroid antibodies, lymphocytic infiltration, fibrosis and atrophy, enlargement of the gland with goitre (Hashimoto’s thyroiditis) Pregnancy ( risk factor ) can lead to transient or permanent hypothyroidism after delivery and can be misdiagnosed as postnatal depression (post-partum thyroiditis) iodine deficiency ( need in synthesis ) Is a preventable cause of neonatal hypothyroidism, which causes severe mental retardation (cretinism) in children. genetic defect Can cause hypothyroidism in infancy (familial thyroid dys-hormonogenesis). Drugs causing hypothyroidism include amiodarone and lithium. Iatrogenic hypothyroidism is caused by intentional treatment of thyroid disease (e.g. surgery), or inadvertent damage from radiation to the head and neck area Treatment: We give thyroxine replacement → measure TSH → if normal  if decrease – will decrease dose secondary hypothyroidism: less common caused by TSH deficiency resulting from hypothalamic–pituitary disease Characterised by:: low fT4 with non-elevated TSH. (normal or low) Treatment T4 should be replaced to the upper part of the normal range because TSH cannot be relied upon as a measure of optimal replacement. Hypothyroidism in special situations ✓ Myxoedema coma (sever hypothyroidism) is a rare medical emergency with a high mortality requiring treatment in a high dependency setting ✓ Children with hypothyroidism can present with poor growth and development or delayed puberty ✓ while young women may present with reproductive symptoms alone, such as menstrual disturbance or reduced fertility Subclinical hypothyroidism normal fT4 with elevated TSH If patients are asymptomatic, treatment may not be needed starting thyroxine if TSH is >10 mIU/L, because of the high likelihood of progression to frank hypothyroidism Treatment should also be considered at lower levels of TSH elevation (TSH 5–10 mIU/L) in women planning pregnancy. In Pregnancy The fetal thyroid gland only develops after 10–12 weeks’ gestation, hence the fetus is reliant on maternal thyroxine before this time. Thyroid replacement should be optimised before conception and/or in early pregnancy. thyroxine dosage is empirically increased by 25–50 μg in early pregnancy Autoimmune hypothyroidism slightly increases the risk of recurrent miscarriage, as well as maternal and neonatal problems. Goitre enlargement of the thyroid gland Thyroid malignancy is rare, but should be considered in any patient presenting with a thyroid lump. Types : Diffuse goitre Riedel’s thyroiditis Thyroid cancer Differentiated thyroid cancer is the most common type is follicular , The prognosis is good if detected early and managed appropriately Medullary thyroid cancer (MTC) C-cell hyperplasia is a precursor to MTC. Serum calcitonin is a tumour marker in MTC , symptoms ::::: flushing, sweating and diarrhea Lab Test Most laboratories use TSH alone to diagnose hypothyroidism. This is sufficient to diagnose primary hypothyroidism, but fT4 must be measured as well as TSH when secondary hypothyroidism is suspected Autoimmune hypothyroidism is confirmed by measuring thyroid antibodies. TPO antibodies are usually strongly positive in Hashimoto’s thyroiditis ( TSH ) Overview Chemistry: glycoprotein composed of two noncovalently linked alpha and beta subunits. α subunit of TSH is identical to that of the other glycoprotein molecules— FSH, LH, (hCG) β subunits differ in these glycoproteins and is responsible for their biologic and immunologic specificity. Function: β subunit of TSH attaches to high-affinity receptors in the thyroid → stimulating iodide uptake→ hormonogenesis → and release of T4 and T3 . This occurs through activation of adenylyl cyclase and the generation of cAMP. Secretion: secretion of TSH is controlled by both stimulatory (TRH) and inhibitory (somatostatin) TSH interacts with specific cell receptors on the thyroid cell surface → rise to 2 main actions. 1. it stimulates cell reproduction and hypertrophy. ( ↑ follicular cells ) 2. it stimulates the thyroid gland to synthesize and secrete triiodothyronine and thyroxine. When hypothalamic-pituitary function is normal, a log/linear inverse relationship between serum TSH and free thyroxine exists. Useful For Screening for thyroid dysfunction and detecting mild (subclinical), as well as overt, primary hypo- or hyperthyroidism in ambulatory patients. Monitoring patients on thyroid replacement therapy. ↓ TSH → → will decrease dose ↑ TSH → → will increase dose Confirmation of thyroid-stimulating hormone (TSH) suppression in thyroid cancer patients on thyroxine suppression therapy. In thyroid cancer → ↑ TSH ( TSHoma , hyperthyroidism )→ we will suppression TSH → Confirmation Prediction of thyrotropin-releasing hormone-stimulated TSH response. if we need stimulating TSH by TRH → conform by measure TSH Reference Values Depending on age , the upper limit will decrease with age Patient For 12 hours before this test do not take multivitamins or dietary supplements containing biotin (vitamin B7) Specimen Serum Preparati on Reject Gross hemolysis Reject \\ HB rejected \\ Gross Lipemia OK \\ Gross icterus OK Lab Test differential diagnosis of :: Interpre primary (thyroid) ↑ TSH tation from secondary (pituitary) TSH ↓ or normal and tertiary (hypothalamus) hypothyroidism ↓ TSH or normal ❖ (TRH) stimulation test :: differentiates all types of hypothyroidism by observing the change in patient TSH levels in response to TRH. In primary hypothyroidism → TSH response to TRH stimulation is exaggerated. In secondary hypothyroidism → TSH response absent. In tertiary hypothyroidism → TSH response delayed. Lab Test Sick, hospitalized patients may have falsely low or transiently elevated TSH. Caution For assays employing Ab → possibility exists for interference by human anti-animal Ab (ie, heterophile Ab) s Interference due to extremely high titers of Ab to analyte-specific antibodies, streptavidin, or ruthenium can occur. TSH concentrations exhibit a diurnal variation , with the peak between 10 a.m. and 4 p.m, does not influence. Method Descript ion Electro-chemiluminescent Immunoassay // Cobas immunoassay biotinylated monoclonal TSH-specific Ab react with a monoclonal TSH-specific Ab labeled with a ruthenium complex → form a sandwich complex → addition of streptavidin-coated microparticles → interaction of biotin and streptavidin → complex becomes bound to the solid phase → Application of a voltage → measured emission by a photomultiplier Lab Test ( T3 ) Useful For Specimen Referenc e Values Patient Second-order testing for hyperthyroidism in patients with low TSH values and normal T4 levels. Diagnosis of triiodothyronine T3 toxicosis serum Depending on age , the upper limit will decrease with age For 12 hours before this test do not take multivitamins or dietary supplements containing biotin (vitamin B7) Preparation Reject Lab Test Cautions Gross hemolysis Reject \\ HB rejected \\ Gross Lipemia OK \\ Gross icterus OK Triiodothyronine (T3) is not a reliable marker for hypothyroidism. not useful for general screening of hyperthyroidism. Therapy with amiodarone can lead to depressed T3 values. Phenytoin, phenylbutazone, and salicylates cause release of T3 from the binding proteins, → leading to a reduction in the total T3 hormone level at normal free T3 levels. Autoantibodies to thyroid hormones can interfere with the assay. Binding protein anomalies ( number or affinity ) → increase affinity of binding → increase total ,, although the patient may be in a euthyroid state Free T3 or free T4 testing is indicated in these cases. hyper total Some patients who have been exposed to animal antigens, either in the environment or as part of treatment or imaging procedures, may have circulating antianimal antibodies present. → interfere Method Descripti on Lilas Electro-chemiluminescence Immunoassay \\ Roche Cobas instrument is a competitive assay: 1. Release Bound T3 is from binding proteins by 8-anilino-1-naphthalene sulfonic acid (ANS). 2. Specimen is incubated with a sheep polyclonal anti-T3 antibody labeled with ruthenium. 3. Streptavidin-coated microparticles and biotinylated T3 are added for a second incubation during which the still free binding sites of the labeled antibody become occupied. 4. The resulting immune-complex becomes bound to the solid phase by interaction of biotin and streptavidin. 5. The reaction mixture is aspirated into the measuring cell where the microparticles are magnetically captured onto the surface of the electrode. 6. Unbound substances are removed and application of a voltage to the electrode induces the electrochemiluminescent emission. 7. This signal is measured against a calibration curve to determine patient results. Overview Reporting Name Useful For Lab Test ( T4 ) Is synthesized in the thyroid gland. T4 is metabolized to triiodothyronine (T3) peripherally by deiodination. T4 is considered a reservoir or prohormone for T3. About 0.05% of circulating T4 is in the free or unbound portion. The remainder is bound to thyroxine-binding globulin (TBG), prealbumin, and albumin. T4 and T3 cause –ve feedback to the pituitary and hypothalamus with resultant suppression or stimulation of the thyroid gland. Measurement of total T4 gives a reliable reflection of clinical thyroid status in the absence of proteinbinding abnormalities and non-thyroidal illness. changes in binding proteins can occur that affect the level of total T4, but leave the level of unbound hormone unchanged. T4 (Thyroxine) Monitoring treatment with synthetic hormones (synthetic triiodothyronine [T3] will cause a low total thyroxine [T4]) Monitoring treatment of hyperthyroidism with thiouracil ( anti-T4 ) and other anti-thyroid drugs Index of thyroid function when the thyroxine-binding globulin (TBG) is normal and non-thyroidal illness is not present. TBG thyroid function TSH Specimen serum Referenc e Values Depending on age , the upper limit will decrease with age Patient For 12 hours before this test do not take multivitamins or dietary supplements containing biotin (vitamin B7) 20 free Preparation Reject Interpret ation Gross hemolysis Reject \\ HB rejected \\ Gross Lipemia OK \\ Gross icterus OK Value more than 11.7 mcg/dL in adults and more than the age-related cutoffs in children are seen in hyperthyroidism and in patients with acute thyroiditis. Values below 4.5 mcg/dL in adults or below the age-related cutoffs in children are seen in hypothyroidism, myxedema, cretinism, chronic thyroiditis, and occasionally, subacute thyroiditis. Lab Test Cautions Pregnancy: ✓ Increased total thyroxine (T4) is seen in pregnancy and patients who are on estrogen medication. These patients have increased total T4 levels due to increased thyroxinebinding globulin (TBG) level. Pregnancy → ↑ TBG → ↑ binding with T3 →↓ turnover of T4 → ↑ T4 total ✓ incomplete release of thyroxine (T4) from its binding proteins might result in falsely low total T4 levels. → total T4 should not be used as the only marker for thyroid function evaluation. Decreased total T4 is seen in patients on treatment with anabolic steroids or nephrosis (decreased TBG levels). (TRH) stimulation test may be required for certain cases of hyperthyroidism. Give TRH → measure TSH, T4 . Clinical findings are necessary to determine if thyrotropin, TBG, or free T4 testing is needed. Thyrotropin (TSH) may be better than T4 as the initial test of thyroid status. Exposed to animal antigens → have circulating anti-animal antibodies→ interfere with the assay.** Autoantibodies to thyroid hormones can interfere with testing** Binding protein anomalies may cause values that deviate from the expected results. ** In rare cases, interference due to extremely high titers of antibodies to analyte-specific antibodies, ruthenium or streptavidin can occur. Method Description This test cannot be used in patients receiving treatment with lipid-lowering agents containing dextrothyroxine (D-T4) unless therapy is discontinued for 4 to 6 weeks to allow the physiological state to become reestablished prior to testing. Electrochemiluminescence Immunoassay Assay interference All test Caution : ❖ If the thyroid results do not fit with the clinical presentation,→ blood should be sent to another laboratory for confirmation by : 1. another method. 2. Or Equilibrium dialysis is the most accurate way to measure fT4, and eliminates the possibility of interfering antibodies affecting the result. ❖ Antibodies to TSH (heterophile antibodies) can make the TSH look falsely high or low, and these can be detected. ❖ Familial dys-albuminaemic hyper-thyroxinaemia (FDH) should also be considered in the context of high fT4 and normal TSH. FDH leads to falsely elevated T4 due to an abnormal albumin, which has a higher affinity for thyroxine than TBG. FDH → increase albumin & affinity →bind T4 → increase total & TSH normal So if we see TSH normal & T4 high → FDH or hyper and have some issue in th. Gland. Distinguishing TSHoma from thyroid hormone resistance SHBG produced by the liver, and is elevated in hyperthyroid states. In TSHoma, → patients are truly hyperthyroid and therefore typically have high SHBG levels, thyroid hormone resistance → low or normal SHBG. TRH injection In TSHoma → flat TSH response thyroid hormone resistance → exaggerated rise hyperthyroidism Patients with TSHoma will usually also display a raised α-subunit, have evidence of a pituitary tumour on MRI PET) ‫اشعة‬ and normalise thyroid function in response to somatostatin analogues T3/T4 ↑ → TSH ↑ → TSHoma , resistance , assay interference