Testing for hypercoagulable syndromes

Adil Abbasi, MD FACP

Some tests (especially functional assays) may be affected by anticoagulation—including LMWH, but genetic/molecular tests are not.

For Protein C, Protein S, Antithrombin III, and some lupus anticoagulant tests:
Results may be altered by LMWH and/or the underlying acute thrombosis.
For Factor V Leiden, Prothrombin G20210A mutation (genetic tests):
Not affected by LMWH or any anticoagulant—can be tested at any time.

Detailed Breakdown by Test

Test	Affected by LMWH?	Affected by Acute PE/Thrombosis?	Comments
Protein C (activity)	Yes (can be ↓)	Yes	May be falsely low; avoid testing acutely or on anticoagulation
Protein S (activity/antigen)	Yes (can be ↓)	Yes	Same as above; also affected by warfarin, inflammation
Antithrombin III (activity)	Yes (can be ↓)	Yes	May be low with heparin and acute thrombosis
Lupus Anticoagulant	Mild effect	Yes	Can give false positives; acute phase + anticoagulant effect
APC Resistance (Factor V Leiden functional)	Yes	Yes	Functional test unreliable; use DNA-based test instead
Factor V Leiden (DNA test)	No	No	Can be done anytime
Prothrombin Gene Mutation (DNA)	No	No	Can be done anytime
Antiphospholipid antibodies (ELISA)	Not significantly	Yes	Can test, but may want to repeat when off anticoagulation
Homocysteine, MTHFR, others	No	No	Can be done anytime

*Acute thrombosis itself (the PE) can lower Protein C, Protein S, and Antithrombin III—can’t always distinguish inherited vs. acquired deficiency during the acute event.

Test Type	Reliable on LMWH?	Best Time to Draw
Genetic (Factor V Leiden, Prothrombin G20210A)	Yes	Anytime
Protein C, Protein S, ATIII	No	Before anticoagulation or ≥2-4 weeks after
Lupus Anticoagulant	Maybe	Ideally off anticoagulation

Anti-coagulants and ordering tests for Hypercoagulable syndromes

Warfarin (Vitamin K Antagonist)

Protein C and Protein S: Profoundly affected; Warfarin reduces Protein C and S levels (vitamin K-dependent factors) within days; results are almost always falsely low while on therapy.
Antithrombin III: Not affected.
Lupus Anticoagulant: Can interfere with certain assays (PT/INR-based) but most tests use aPTT-based or DRVVT, which may be less affected.
Genetic Tests: Not affected.

Direct Oral Anticoagulants (DOAC) - (Apixaban, Rivaroxaban, Edoxaban, Dabigatran):

Protein C, Protein S, Antithrombin III:

Generally, not directly affected—but acute thrombosis itself may lower levels.

Lupus Anticoagulant:

DOACs can cause false-positive or indeterminate lupus anticoagulant results (especially with DRVVT and aPTT-based tests).

Genetic Tests: Not affected.

Subcutaneous Unfractionated Heparin (SQ UFH):

Effects on Hypercoagulable Testing:

Similar to IV UFH and LMWH:

Can lower antithrombin III.
Mild to moderate effect on functional assays for Protein C/S.
Can interfere with some lupus anticoagulant assays (especially aPTT-based).

Genetic tests are not affected.

LMWH: Same as for SQ UFH/IV UFH.

Acute Thrombosis

Regardless of anticoagulant, the acute phase of thrombosis itself can reduce Protein C, Protein S, and Antithrombin III, leading to false low levels.

Table

Drug/Class	Protein C/S Reliable?	Antithrombin III Reliable?	Lupus Anticoagulant Reliable?	Genetic Tests Reliable?	Comments
Warfarin	NO	Yes	Maybe	Yes	Wait ≥2–4 weeks off drug for C/S
DOACs	Yes*	Yes*	NO	Yes	LA results unreliable on DOACs
LMWH	No	No	Maybe	Yes	Wait ≥2–4 weeks off drug
IV/SQ UFH	No	No	Maybe	Yes	Similar to LMWH

*Best results if off the drug and not in the acute phase.

Summary: Draw blood for hypercoagulable testing before starting any anticoagulant.

If already on anticoagulation:

Genetic tests (Factor V Leiden, Prothrombin) can be done at any time.
Functional assays (Protein C/S, ATIII): Wait 2–4 weeks off anticoagulation and ensure acute thrombosis has resolved.
Lupus Anticoagulant: Avoid testing on DOACs; may be possible on heparin/warfarin but interpret with caution; If results are indeterminate, repeat off anticoagulation.

References:

Bates SM, et al. NEJM, 2023. “Diagnosis of Thrombophilia in Venous Thromboembolism.”
CHEST Guideline, 2021 (Hypercoagulable Testing in Acute VTE).
ASCP Quick Guide: When to Test for Thrombophilia.