Saturday, September 29, 2007

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

0503211E

11 comments:

VASTYJ said...

hello Kai Lin!

hmm, i would like to know if this 50% PT and APTT is a very specific test to check for the presence of inhibitors in prolonging the clotting time? Or does it only serve as a guideline for doctors to follow.

Valerie XD

MedBankers said...

Hi,

How do the inhibitors inhibit the coagulation factors? And what causes the presence of these inhibitors in the first place? Genetics? In a normal person, is there supposed to be any of these inhibitors present, or there is a normal trace amount?

Thanks!

- Debra, tg02

first6weeks said...
This comment has been removed by the author.
first6weeks said...

Hihi Kailin! =)
Is there any particular reason why the plasma has to be incubated in water bath?

June, TG02

royal physicians said...

Hey Kai Lin

Sorry if my question is kinda stupid but just wanna clarify with you. With clotting factor deficiency, your coagulation time will increase rite? Then if u were to add normal plasma, if it doesn contain inhibitors then your coagulation time should return to normal? Thanx

Johanna
0503309G
TG02

first6weeks said...

hihi

just wondering, in what situation the doctor wll request this test?

Juexiu
tg02

MedBankers said...

Harlow...

may i noe are there any tests done to determine what specific inhibitor(s) present in the patient's plasma??

eunice
0503245C

Star team said...

hello kailin

the lab i'm with uses an analyzer to determine APTT and PT. Is there tendency for human error to occur while using the manual method to determine APTT and PT?

phuiyuen, TG02

MedBankers said...

hey,

if the result turned out to be out of the normal range, what will yr lab do? re-run or do another confirmation test?

elaine

first6weeks said...

hey valerie,

it only serves as a guideline.
test against specific inhibitor must be carried out to determine whether that specific inhibitor is present

hey debra,

there are presece of natural inhibitors in our plasma such as Antithrombin II, protein C and protein S.
take protein C and protein S as an example. protein C and protein S together inhbit the action of factor VIII.

hey june

the temperature for the water bath is at 37degrees which is normal body temperature.
coagulation reactions take place in normal body temp.

hey johanna,

with clotting factor deficiency, the clotting time will be prolonged. the addition of normal plasma( with presence of all clotting factors) would have corrected the clotting time if there is deficient clotting factor.
yup. the clotting time will be back to noraml.


hey juexiu

PT and APTT can be used as a monitoring test for heparin and fibrinolytic therapy.

hey eunice

ya, there is. one such test is factor VIII inhibitor assay.

hey phui yuen

yea. there is bound to be human errors. to minimise the errors,we will take two readings and the second reading for PT/APTT must agree within 10% of the shorter clotting time. We will calculate the average of the two readings obtained.

hey elaine,

repeat of PT and APTT will be done if PT is <8 sec and APTT < 26s.

first6weeks said...

hey valerie,

it only serves as a guideline.
test against specific inhibitor must be carried out to determine whether that specific inhibitor is present

hey debra,

there are presece of natural inhibitors in our plasma such as Antithrombin II, protein C and protein S.
take protein C and protein S as an example. protein C and protein S together inhbit the action of factor VIII.

hey june

the temperature for the water bath is at 37degrees which is normal body temperature.
coagulation reactions take place in normal body temp.

hey johanna,

with clotting factor deficiency, the clotting time will be prolonged. the addition of normal plasma( with presence of all clotting factors) would have corrected the clotting time if there is deficient clotting factor.
yup. the clotting time will be back to noraml.


hey juexiu

PT and APTT can be used as a monitoring test for heparin and fibrinolytic therapy.

hey eunice

ya, there is. one such test is factor VIII inhibitor assay.

hey phui yuen

yea. there is bound to be human errors. to minimise the errors,we will take two readings and the second reading for PT/APTT must agree within 10% of the shorter clotting time. We will calculate the average of the two readings obtained.

hey elaine,

repeat of PT and APTT will be done if PT is <8 sec and APTT < 26s.