Principle: Both PT and APTT tests are used for the investigation of haemostatic failure. The prothrombin time (PT) tests for factors I, II, V, VII, X of the extrinsic system whereas the activated partial thromboplastin time (APTT) tests for all factors in the intrinsic system (factors I, II, V, VIII, IX, X, XI, XII). For PT, the time between the addition of tissue thromboplastin to the presence of a detectable clot is the prothrombin time; ref range 9.2-11.2s.
For APTT, the citrated plasma is incubated with APTT reagent (for the activation of contact factors) after which CaCl2 is added and the clotting time is measured; ref range: 27.0-36.1s.
Procedure:
1) Check if the received requisition form tally with the patient sample. Make sure that the level of blood is above the marker found on the tubes.
2) Stamp and label form and test tube.
3) Centrifuge the tubes for 3000rpm for 180s.
4) Put the tubes in the rack and placed into analyzer. Order test through the computer system.
5) Record results. PT<8.0s, APTT<26.0s and delta check indicate that test have to be repeated (to make sure it is not a random error).
6) Results will then be keyed into the LIS.
QC: Level I and II controls (used in sysmex CA-1500) are performed at an interval for every batch of 40 samples. Results that are out-of control may indicate that the QC is expired, analyzer has problem, reagent has problem.
here is a very simplified coagulation cascade:
When: -PT ↑
-APTT normal
Most likely is F VII deficient.
-PT ↑
-APTT ↑
F X, V, II, I deficient.
-PT normal
-APTT ↑
Most likely F XII, XI, IX, VIII deficient.
Eunice
tg02
0503245C
11 comments:
hi eunice! wah coag lab quite cheem, i dun want to spend my 4weeks there leh...
okay qns for u
1)Will the machine alert u after every 40samples are tested?
2)If the control is out of range, so u have to re-test the previous 40 samples? if that's the case it will lower the efficiency of work.
Chaur Lee
TG01
hey sister!
U didnt mention about maintenance.. Do u do maintenance for the analyzer everyday ? if yes, how?
haha, see you tml.
Jo-anne Loh
TG02
hi eunice!
just wondering if the level of blood is not above the marker found on the tubes, can the test be continued? or there is a need to stop and re-collect the sample?
oh then is there any manual tests being carried out other than the tests being carried out by the analyzer?
-Sharon Ang.
TG02
0503219H
Hello Eunice,
Can you explain the term 'citrated plasma'? Does it refer to blood sample stored in sodium citrate tube? And if so, why is sodium citrate preferred as an anticoagulant in coagulation studies than say, EDTA or heparin? :P
Looking forward to your reply. Thanks.
- Alex Tg02
hey eunice,
is there a reason why Level I and II controls are performed at an interval for every batch of 40 samples?
Andre, TG01
helloooo eunice..
it's the same machine used in the haem at my side. but i was attached there for a few days only. thanks so much for sharing... ^_^ I'm also curious how often you do system priming? we do it everyday here.
Hi Eunice;)
I was just wondering... you said
"For APTT, the citrated plasma is incubated with APTT reagent (for the activation of contact factors) after which CaCl2 is added and the clotting time is measured; ref range: 27.0-36.1s."
What is citrated plasma and why do you need to add CaCl2?
CASS TG02
Hey eunice, excuse my goondu question, but why is there a need to centrifuge the sample? doing so will cause the coagulation factors to form at the bottom right? whats the whole point of that?
- Debra, tg02.
Hi Eunice
After centrifugation, do you need to check if the serum is haemolyzed, jaundiced or cloudiness? Thanks
Ci Liang
TG01
Qns:Will the machine alert u after every 40samples are tested?
Ans:The machine will nt alert us and so we have to take note of the no. of samples we hae done--can c frm barcode label.
Qns: If the control is out of range, so u have to re-test the previous 40 samples?
Ans: If the control is out, we have to check whether is the ctrl expired/analzer problem etc. If reagent is the one that is causing the problems then have to re-run all the samples.
Qns:Do u do maintenance for the analyzer everyday ?
Ans:Maintenance is done every morning(start-up) and at 4pm. There is a checklist for the analyzer where we have to rinse the probe and do priming etc.
Qns: if the level of blood is not above the marker found on the tubes, can the test be continued?
Ans:If the lvl of blood is below the marker, we have to reject the sample as this will mean the proportion of sodium citrate and blood is incorrect and will affect the result. Manual test is done when the analyzer has some problems in detecting the clot.
Qns:Can you explain the term 'citrated plasma'? why is sodium citrate preferred as an anticoagulant in coagulation studies than say, EDTA or heparin?
Ans: Citrated plasma means that the blood sample contains sodim citrate. Sodium citrate is used bcos the chelation of Ca2+ is reversible and will allow clotting to occur when reagent is added. EDTA will complex Ca2+ permanently and heparin is not used cos it can affect APTT.
Qns:why Level I and II controls are performed at an interval for every batch of 40 samples?
Ans:The ctrls are run at every 40 samples bcos if the no. of samples is too many and an error is spotted, u have to re-run all the samples and this will take up alot of time.
Qns:how often you do system priming?
Ans: Priming is done once a day-according to the checklist.
Qns: why do you need to add CaCl2?
Ans:For APTT, tissue thromboplastin is not added and when CaCl2 is added, calcium will restart the coagulation cascade and cause the formation of clot where the time is measured.
Qns: why is there a need to centrifuge the sample?
Ans:Centrifuge the samples is to spin down the RBCs, WBCs and platelets so that the plasma is at the upper portion of the tube and the coagulation factors will b in the plasma. RBCs, WBCs and platelets will affect the test.
Qns: After centrifugation, do you need to check if the serum is haemolyzed, jaundiced or cloudiness?
Ans: After centrifuge, we have to check if samples is haemolysed. If so, we have to report and the result will b affected and nt b accurate.
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