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Lupus Anticoagulant Testing: Details

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Also known as: LA; Lupus Anticoagulant Panel; Lupus Inhibitor; LA Sensitive PTT; PTT-LA; Dilute Russell Viper Venom Test; DRVVT; Modified Russell Viper Venom Test; MRVVT
Formal name: Lupus Anticoagulant
Related tests: Antiphospholipid Antibodies; Hexagonal Phase Phospholipid Neutralization Assay; PTT; Thrombin Time; Cardiolipin Antibodies; PT and INR; Beta-2 Glycoprotein 1 Antibodies; Kaolin Clotting Time; Platelet Neutralization Test; Factor V Leiden Mutation and PT 20210 Mutation; Homocysteine; Protein C and Protein S; Antithrombin

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The following table summarizes some LA testing results that may be seen.

  Tests Results Possible Interpretation
Step 1 LA-sensitive PTT (PTT-LA) and/or dilute Russell viper venom test (DRVVT)

Normal

Usually no further testing is done. If there is a strong suspicion of the presence of an inhibitor, then testing may be repeated.
    Prolonged Possible inhibitor present; see Step 2
Step 2 Mixing study: Mix equal parts patient plasma with normal pooled plasma and perform PTT-LA or DRVVT

Normal

The initial test results were prolonged due to a cause other than an inhibitor, i.e., deficiency in coagulation factor(s).
    Prolonged If mixing patient plasma with normal pooled plasma does not "correct" the result, then it is likely that lupus anticoagulant is present; see Step 3
Step 3 Confirmation (correction or neutralization test): perform PTT-LA or DRVVT again but add excess phospholipids (e.g., hexagonal phase phospholipid neutralization assay). A ratio is calculated by dividing this result into the result of PTT-LA or DRVVT without excess phospholipids.

Positive (high ratio)

If the ratio is above a specified cutoff, then presence of lupus anticoagulant is suggested.
    Negative (low ratio) A specific inhibitor rather than lupus anticoagulant may be present. Tests for antibodies directed against coagulation factors, specifically factor VIII, may be performed.

Based on the International Society of Thrombosis and Hemostasis (ISTH) recommendations, there are four criteria that must be met to confirm the presence of LA:

  • Prolonged result on at least one of two coagulation tests that are dependent on phospholipids, such as PTT-LA or DRVVT
  • Prolonged result on a mixing study (evidence of clotting inhibition)
  • Shortened clotting time occurs after adding excess phospholipids (demonstrates dependence of the inhibitor on phospholipids)
  • Ruling out coexisting specific coagulation factor inhibitor, such as factor VIII, which could result in catastrophic bleeding if not identified
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