Our patient was unwell with pneumonia. The results showed an isolated prolonged APTT:
- PT 14s (11-14s)
- APTT 48s (33-40s)
- APTT 50:50 mix 47s
- Fibrinogen (Clauss) 4.9g/L (1.5-4.5g/L)
- Thrombin time 16s (15-19s)
She was not on any anticoagulation and had no bleeding history or family history. It would be unusual to pick up a bleeding disorder in a 59 year old but not impossible! Looking back through previous results there had been no abnormalities and on repeat the results are similar. Because the APTT is not correcting after the administration of normal plasma to the tube it seems likely that there is an inhibitor or antibody interfering with the assay. The most likely cause is the lupus anticoagulant. So called that it was first associated with patients who have systemic lupus erythematous and as it prolongs the coagulation times in the lab (NOT in the patient!). Like any other antibody they can be stimulated by infection, inflammation, autoimmune disease and malignancy. Most commonly they are transient and require no further investigation. Patients should receive LMWH prophylaxis as per usual protocols and undergo surgical procedures if needed. Patients should be examined and questioned for any of the causative medical problems and the test should be repeated in 3-4 months. If the patient has recurrent clots then it may be a sign of the antiphospholipid syndrome.
In this patient she had no signs of autoimmune disease or malignancy. The DRVVT ratio was 1.9 confirming the lupus anticoagulant. On repeat four months later the coagulation screen was normal.
Here is a crib sheet for working out what’s going on if the APTT is prolonged. It is not fool proof and policies and procedures will vary between laboratories. As always ask!
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