Question 3.1

 54 year old male presents with a right deep vein thrombosis and haemoptysis. These blood results are from his admission.



Normal range


12 sec



69 sec


Thrombin time

16 sec


APTT mixing test

60 sec

a) What is the APTT mixing test and its significance in this patient?

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College Answer

It involves 1 to 1 mixing patients plasma with normal pooled platelet free plasma. If it normalises then the elevated APTT is due to factor deficiency. Partial correction suggests an inhibitor.

The results probably suggest an antiphospholipid syndrome in this patient


The coagulation tests are discussed in greater detail elsewhere.

This question closely resembles Question 8.3 from the first paper of 2011.

The mixing studies test for the presence of coagulation inhibitors. The patient's plasma is mixed 50:50 with a random sample, and if a coagulation inhibitor is present the resulting mixture will still have a raised APTT, whereas if a factor deficiency was responsible the APTT will normalise.

In this patient, there is clearly some sort of anticoagulant factor present.


Hunt, Beverley J. "Bleeding and coagulopathies in critical care." New England Journal of Medicine 370.9 (2014): 847-859.