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Lupus anticoagulant (LA)

Coagulation · also called LA screen, dRVVT, Lupus inhibitor

What it measures

Detects antiphospholipid antibodies that prolong phospholipid-dependent clotting tests in vitro but increase clot risk in the body. Part of the work-up for antiphospholipid syndrome, recurrent thrombosis and pregnancy loss.

Specimen and preparation

Specimen: Double-centrifuged, platelet-poor citrated plasma
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Preparation: Test when not on anticoagulants if possible; DOACs and heparin cause false results. Repeat positives after 12 weeks.

Reference range

Group	Range
dRVVT screen/confirm ratio	<1.2 (negative) ratio
All	Not detected

Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.

Causes of high values

Positive: antiphospholipid syndrome
Systemic lupus erythematosus
Infections and certain drugs (transient)
Anticoagulant interference (false positive)

Method

Two tests: dilute Russell viper venom time (dRVVT) and LA-sensitive aPTT, each with screen, mix and confirm steps

Good to know

Diagnosis of antiphospholipid syndrome requires persistent positivity plus clinical events; combine with anticardiolipin and anti-β2-glycoprotein I antibodies.

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