University:
College
Course:
Medical Laboratory Science
Academic year:

2023
Views:

87

Pages:

1
Author:

Carlo M.

HEMATOLOGY LABORATORY ACTIVATED PARTIAL THROMBOPLASTIN TIME OUTLINE • Activated Partial Thromboplastin Time o Principle o Materials & Reagents o APTT Procedures LABORATORY EVALUATION OF SECONDARY HEMOSTASIS: ACTIVATED PARTIAL THROMBOPLASTIN TIME • • The activated partial thromboplastin time differs from PTT for that in the former, a activator (to ensure maximal activation) is added to the plasma. The APTT allows for maximum activation of the contact factors and gives more consistent and reproducible results. The PTT and APTT are useful screening procedures of coagulation disorders in the intrinsic and common pathways except for platelets and factor XIII. Thus, the test will detect deficiencies of factors II, V, VII, XI and XII. The PTT and APTT are much more sensitive to coagulation factpr deficiencies than the whole blood clotting time. When the PTT and APTT are abnormally prolonged there may be a deficiency in one of the coagulation factors involved in the intrinsic and common pathways, or an inhibitor of coagulation may be present. An abnormally shortened APTT may be caused by partial clotting of the blood as a result of a traumatic venipuncture, high levels of factor III, DIC or the presence of the platelets in the plasma. PRINCIPLE • • • The calcium in whole blood is bound by the sodium citrate anticoagulant to prevent coagulation. The plasma after centrifugation contains all intrinsic coagulation factors except calcium and platelets. Calcium and phospholipid substitute for platelets (partial thromboplastin) are added to the plasma. The time required for the plasma to clot is the partial thromboplastin time. The procedure in APTT is similar to the original test. PTT except that a standardized foreign inert surface is introduced to the plasma, which speeds up the formation of fibrin polymer. APTT and PTT are useful screening procedures for coagulation factor deficiencies or dysfunctional factor of the intrinsic and common pathway of coagulation, except platelets and factor XIII. These tests also screen for the presence of circulating anticoagulants directed against the factors involved in the two pathways. These tests ca also monitor oral anticoagulant therapy like in Coumadin and dicumarol. MATERIALS & REAGENTS • • • • • • • Two way needle Citrated evacuated tube Centrifuge 0.3 ml serological pipette 0.4 ml serological pipette Tissue paper Timer • • • • Calcium chloride aPTT reagent 37oc water bath Wasserman tube APTT PROCEDURES PREPARATION OF SPECIMEN FOR APTT 1. 2. 3. Collect venous blood on a citrated tube. Centrifuge at 1,500 rpm for 5 minutes. Separate the plasma by placing it into a clean dry tube. TEST PROCEDURE 1. 2. 3. 4. 5. 6. 7. 8. • Pipette into prewarmed test tube Plasma/ control 0.1 ml Incubate 1-2 minutes at 37oc Add aPTT reagent 0.1 ml Incubate 1-2 minutes at 37oc Add prewarm CaCl2 0.1 ml Start timer with addition of CaCl2 Record time required for clot formation Note: Prewarm CaCl2 (0.02 mol/L) to 37oc. EXPECTED VALUES • • • Results: o Calculate the mean time of duplicate aPTT o Determinations for each test plasma and report to the nearest 0.1 seconds. Reference value: 23.4 – 36.2 seconds