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Sally Mandour: Lupus Anticoagulant-The Tree Key Diagnostic Criteria

Sally Mandour/LinkedIn

Oct 26, 2026, 15:37

Sally Mandour: Lupus Anticoagulant-The Tree Key Diagnostic Criteria

Sally Mandour, Associate Professor, Head of Hematology Unit at Clinical Pathology Department of National Liver Institute, Monofeya University, shared a post on LinkedIn:

“Lupus Anticoagulant Understanding

‘A positive test for a negative name’.

One of the most counterintuitive concepts in coagulation:

a ‘lupus anticoagulant‘ doesn’t cause bleeding in vivo – it’s associated with thrombosis.

The name comes purely from its behaviour in vitro, where it prolongs phospholipid-dependent clotting tests.

The ISTH minimum diagnostic criteria require proving three conditions:

An abnormality in phospholipid-dependent coagulation (a prolonged APTT or PT).
That the abnormality is caused by an inhibitor, not a factor deficiency.
That the inhibitor is phospholipid-dependent, not a specific factor inhibitor.

How each criterion gets tested:

Criterion 1 – A phospholipid-based clotting assay (APTT, PT, dRVVT, KCT, or PTT-LA)
Criterion 2 – A 1:1 mixing study with normal plasma. If the clotting time corrects then factor deficiency. If it stays prolonged then an inhibitor is present. (A second tube is incubated 1–2 hours to also exclude a specific-factor inhibitor.)
Criterion 3 – Repeating the test with varying phospholipid concentrations. If adding more phospholipid shortens the clotting time, the inhibitor is phospholipid-directed – consistent with LA.

The workhorse test: dRVVT.

Russell’s viper venom directly activates Factor X, bypassing the intrinsic pathway’s earlier steps.

The result is reported as

a screen ratio,
a mix ratio (patient plus normal plasma, 1:1), and
a confirmation ratio (high vs low phospholipid concentration).

And the pattern across all three determines the interpretation, not any single number in isolation.

Common traps:

Residual platelets in frozen plasma – false negatives (hence double centrifugation before freezing).
Anticoagulants (heparin, warfarin, DOACs) -false positives.
dRVVT alone cannot distinguish LA from a Factor V or VIII inhibitor.
LA must be confirmed as persistent (at least 12 weeks apart) before diagnosing antiphospholipid syndrome.

Sally Mandour: Lupus Anticoagulant-The Tree Key Diagnostic Criteria