Predisposing factor | Prevalence in the western countries | Thrombotic risk as compared with general population (approximately) |
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Factor V Leiden (APC resistance, FV Leiden, FV R506Q, FV G1691A) heterozygous | 3-8% | Low-risk thrombophilia 3 × |
Factor V Leiden (APC resistance, FV Leiden, FV R506Q, FV G1691A) homozygous | <0.2% | High-risk thrombophilia >30 × |
G20210A point mutation in the prothrombin gene, heterozygous | 0.7-4% | Low-risk thrombophilia 3 × |
G20210A point mutation in the prothrombin gene, homozygous | <0.1% | High-risk thrombophilia >30 × |
Protein C deficiency1) | 0.2-0.5% | High-risk thrombophilia 10 × |
Protein S deficiency2) | 0.2-0.5% | High-risk thrombophilia 10 × |
Antithrombin deficiency 3) | 0.02-0.1% | High-risk thrombophilia Great variation between families, up to > 100 × |
1) Either quantitative deficiency of protein C (Type 1 deficiency) or qualitative impairment of its functional activity (Type 2 deficiency). Over 160 gene defects have been described. A single mutation (PC W380G) causes the majority of type 2 protein C deficiency cases in Finland. 2) Either quantitative deficiency of protein S or qualitative impairment of its functional activity. Over 200 gene defects have been described. 3) Either quantitative deficiency of antithrombin (Type 1 deficiency) or qualitative impairment of its functional activity (Type 2 deficiency). The thrombotic risk is related to the type and degree of the deficiency. Over 100 different gene defects are known. In Finland, type 2 deficiency is caused predominantly by a single mutation (Pro73Leu). | ||||||||||||||||||
Causes of acquired (non-inherited) thrombophilia
Antiphospholipid antibodies
Clinical significance of antiphospholipid antibodies. The risk of thrombosis increases moving down in the Table.
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* So-called Sydney criteria, ISTH 2006 | ||||||||||||||||||
Increased factor VIII activity
Homocysteinaemia
Latent malignancy
Indications for aetiological investigations of thrombophiliaVenous thrombosis and pulmonary embolism
Arterial thrombosis
Asymptomatic people
Laboratory examinations and their timingThrombophilia tests
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*If the screening test for thrombophilia is positive, testing should be followed up with a confirmatory test | ||||||||||||||||||
A sample for thrombophilia testing should primarily be taken one month after the end of treatment. The minimum intervals in special situations are ≥ 2 weeks, ≥ 2-4 days and ≥ 24 hours for warfarin, DOACs and LMWH, respectively. In any case, please check the practice at your laboratory. | ||||||||||||||||||
The sample can be taken at the acute stage before starting anticoagulant therapy but it should then be noted that reactions associated with the acute situation often cause transiently abnormal findings. | ||||||||||||||||||
Any preceding use of anticoagulants and the date of their discontinuation should be indicated on the laboratory request form. | ||||||||||||||||||
If it is not possible to stop the anticoagulant therapy, reliable thrombophilia testing can still be carried out to some degree during the therapy, although this is rarely necessary. In such a case, it is imperative that the current medication is indicated on the laboratory request form.
References
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