Thrombophilia laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Asiri Ediriwickrema, M.D., M.H.S. [2]
Overview
- There are specific laboratory findings associated with each inherited thrombophilias.
- Refer to page on screening for recommendations regarding thrombophilia testing.
Laboratory Findings
Timing
The timing of tests is very important as it influences the levels of various thrombogenic factors in the body.
- Testing at the time of acute venous thrombosis is not indicated or during ongoing anti-coagulation.
- Best time to test is 4 weeks after completion of anticoagulation.
- Avoid intercurrent severe illness
- Pregnancy, oral contraceptives, hormone replacement therapy and cancer chemotherapy may also affect some tests.
- Factor V Leiden and Prothrombin mutation can be done in patients on anticoagulants and even in acute phase, as these are PCR tests. However, other tests can be done only at a later stage to rule out two disorders.
Type of tests
Tests for thrombophilia are categorized according to their priority, as discussed below:
| Priority | Timing | Test | Associated Diagnosis |
|---|---|---|---|
| High | Complete blood count | General | |
| Coagulation studies: INR, prothrombin time, partial thromboplastin time | General | ||
| Factor V Leiden mutation studies | Factor V Leiden | ||
| Prothrombin 20210 gene mutation | Prothrombin G20210A | ||
| Lupus anticoagulant | Antiphospholipid syndrome | ||
| Intermediate | Anticardiolipin antibodies | Antiphospholipid syndrome | |
| Delay 6 months | Functional assay for antithrombin (antithrombin-heparin co-factor assay) | Antithrombin deficiency | |
| Delay 6 months | Protein C functional assay (preferred over plasma protein levels) | Protein C deficiency | |
| Delay 6 months | Free protein S immunoassay | Protein S deficiency | |
| Factor VIII level (use c-reactive protein as control) | Factor VIII disorders | ||
| Flow cytometry | Paroxysmal nocturnal hemoglobinuria | ||
| Peripheral blood smear, JAK2 mutation studies | Myeloproliferative disorders | ||
| Homocysteine level | Hyperhomocysteinemia | ||
| Vitamin B12 level | Hyperhomocysteinemia | ||
| Low | Thrombin time | General/Fibrinogen disorders | |
| Fibrinogen level | Fibrinogen disorders | ||
| Reptilase time | General/Fibrinogen disorders | ||
| Plasminogen level | Plasminogen disorders | ||
| Factor IX activity | Factor IX disorders | ||
| Factor X activity | Factor X disorders |
Variability in thrombophilia testing
- Warfarin: Decreases protein C and S levels
- Heparin: Decreases antithrombin activity and interferes with evaluation for antiphospholipid antibody
- Acute thrombosis: Decreases antithrombin, protein C, and protein S levels