Hello everyone!! It’s my turn to blog for the week. I am currently at coagulation lab. The test which I am going to share with you guys is 50%PT/APTT. I suppose you should be familiar with PT and APTT which we had done before in during haematology lab session. Does it ring a bell? To refresh your memory…

PT is used to screen for abnormalities of those factors that are involved in the extrinsic pathway (factor 5,7,10) and prothrombin and fibrinogen.

APTT is sensitive to deficiencies of factor II,V,VIII,IX,X,XI,XII( Factor 2,5,8,9,10,11,12) involved in the intrinsic pathway.


Test: PT

1) PT reagent is incubated in water bath at 37 degrees for 3mins
2) 0.1ml of test plasma is incubated in 37 degrees water bath for 3mins
3) 0.2ml of PT reagent was pipette into the 0.1ml of test plasma after the incubation period
4) start the stopwatch simultaneously and shake the test tube to mix the contents well and observed for clot

Test:APTT

1) 0.1ml of APTT reagent and 0.1ml of calcium chloride was incubated in water bath at 37 degrees for 5mins
2) 0.1ml of test plasma was added to 0.1ml of APTT reagent. Remember to shake the tube to mix the contents well
3) the tube was placed at 37 degree water bath for 4mins
4) 0.1ml of calcium chloride was pipette into the plasma and APTT reagent
5) start the stop watch simultaneously and observed for clot





Test: 50%PT and APTT correction test

Intended use:
It is used to screen for the presence of inhibitors in patient’s plasma.

Principle:

50% addition of normal plasma is sufficient to restore the deficient factor. Complete or partial correction time suggests a clotting factor deficiency, whereas failure to correct the clotting time suggest the presence of inhibitors. Normal plasma contains all coagulation factors and is mixed with patient’s plasma to detect the presence of circulating inhibitors in the patient’s plasma. If a factor deficiency is responsible for the abnormal clotting time addition of normal plasma should provide the deficient factors and correct the PT and APTT time. However if abnormal clotting time is caused by a circulating inhibitors in the patient’s plasma, the clotting time will remain prolonged even when normal plasma is added. The inhibitor inhibits factors in normal plasma as well as in the patient’s plasma.

Example: if the patient’s PT is 18secs
Normal plasma is 12secs
Average is (18+12)/2=15secs
PT is corrected if 50%PT <15secs>

that's all! feel free to ask if in doubt..

kai lin

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