Cite this page: Parsons JC. Lupus anticoagulant. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/coagulationlupusanticoag.html. Accessed January 18th, 2021.
Definition / general
- Also called lupus inhibitor
- One of the two main types of antiphospholipid antibodies (other is anticardiolipin antibodies)
- Common in patients with systemic lupus erythematosus, but most cases occur in patients without SLE (Arch Pathol Lab Med 2002;126:1424, Firestein: Kelley's Textbook of Rheumatology, 9th Edition, 2012)
- May cause increased PTT (not time dependent), increased or normal PT
- Prolongs clotting times by binding to phospholipid cofactors in coagulation cascade; often not true for HIV+ patients (Arch Pathol Lab Med 1993;117:595)
- Indications:
- Patients with venous thromboembolism (particularly if no family history or associated with autoimmune disease)
- Unexplained stroke (young person or autoimmune disease), cerebral venous thrombosis, recurrent or late pregnancy loss
- May be considered for arterial thrombosis (particularly in young patient or no documented atherosclerosis)
- Specimen: plasma (citrate tube)
Diagnosis
- An algorithm combining several tests is necessary
- All are clotting time based:
- Russell viper venom time (sensitive to abnormalities in factors X and V, diluted for screening)
- Kaolin clotting time
- Dilute PT (tissue thromboplastin inhibition test)
- PTT-based assays (should have low concentration of phospholipids to enhance sensitivity)
- Less commonly Textarin (obtained from venomous Australian snake, not sensitive to abnormalities of factor X but sensitive to abnormalities of factor V
- Less commonly Taipan venom (insensitive to abnormalities of factors X or V)
- Note: all venom assays are sensitive to abnormalities in factor II, calcium and platelets
- Use of commercially available integrated test systems is recommended:
- Staclot procedure: add diluent to tube 1 and egg phosphatidylethanolamine to tube 2
- Add platelet poor plasma with polybrene (neutralizes heparin) to both tubes, incubate and add PTT reagent
- PTT in tube 2 should be 12+ seconds shorter than tube 1 to be a positive test for lupus anticoagulant
- To demonstrate persistence, positive test must be confirmed by repeat testing after 6 - 12 weeks
- Screening assay has low concentration of phospholipids to enhance sensitivity
- Should have platelet count less than 10K
- Abnormal (prolonged) PTT results may be repeated after mixing with equal amount of normal platelet-poor plasma
- Continued prolongation of clotting time indicates an inhibitor (not a factor deficiency)
- Confirmed by adding excess phospholipids, which should shorten clotting time towards normal
- Must also rule out factor VIII inhibitors, heparin and other coagulopathies
- Values prolonged by bivalirudin, lepirudin, argatroban and fondaparinux (Arch Pathol Lab Med 2004;128:1142)
- Results vary based on dilutions in factor XII, XI, IX and VIII assays
- May be mistaken for a factor VIII inhibitor if dilutions to abnormal factor assays are not done
- Don’t test patients being treated with anticoagulants (or interpret with caution)
