A Thrombophilia Screen comprises:
- Antithrombin (previously called Antithrombin III)
- Protein C
- Protein S
- Lupus Anticoagulant
- Factor V Leiden
- Prothrombin Gene Mutation
- anti-β-2-Glycoprotein-1 antibodies
- anti-Cardiolipin antibodies
Thrombophilia is a broad medical term which describes a multifactorial condition where the blood has an increased tendency to clot and is considered hypercoagulable. This condition can render individuals at greater risk of pathological thrombosis and may be either inherited, acquired or a combination of the two.
The Thrombophilia Screen is a combination of tests designed to provide evidence of inherited deficiencies of naturally occurring anticoagulants; Antithrombin, Protein C, and Protein S. The association of prothrombin gene and Factor V Leiden mutations with an increased risk for venous thrombosis has been well documented, and along with lupus anticoagulant and antibodies associated with anti-phospholipid syndrome are included in the Thrombophilia Screen.
Patients who have thrombophilia can present with both venous and/or arterial thrombosis. The location of thrombi can in some cases influence laboratory testing, for example, venous thrombosis is usually associated with a deficiency in anticoagulant activity whereas arterial thrombosis is usually due to a platelet or vascular disorder. In patients who have thrombophilia as a result of a lupus anticoagulant, thrombosis can occur in both venous and arterial systems. Conversely, some patients with protein S deficiency present with arterial thrombosis. Genetic causes are typically recurrent, present in young adulthood and can present in unusual sites such as the mesenteric, hepatic, portal or cerebral circuits e.g. resistance to activated protein C (APCR) due to the factor V Leiden (FVL) mutation. Acquired thrombophilias usually present later in life, e.g. LA or occur due to a different underlying disorder e.g. some patients with myeloproliferative disorders develop hepatic vein thrombosis referred to as the Budd-Chiari syndrome.
Current laboratory (adult) normal ranges are as follows:
- Antithrombin: 80 – 129%
- Protein C: 72 – 156%
- Protein S: Male 70 – 148%, Female 56 – 145%
- Lupus: Ratio ≥1.2 indicates a positive result Anticardiolipin
- IgG: 0 – 10 U/ml
- Anticardiolipin IgM: 0 – 10 U/ml
- Anti-β-2-Glycoprotein IgG: 0 – 7 U/ml
- Anti-β-2-Glycoprotein IgM: 0 – 7 U/ml
Result interpretation is provided by the scientific and clinical team.
The volume of blood in coagulation samples must lie within the volume range as indicated by the size of the black fill arrow present on tubes. Volumes above or below the arrow will result in sample rejection to ensure validity of results.
- Urgent: 4 hours
- Routine: 3 weeks
- 5 blue top (sodium citrate) sample
- 1 yellow top (SST) sample
All coagulation tubes must be adequately filled (see above). All coagulation tubes must be mixed several times by gentle inversion immediately after venepuncture. Mixing the sample with the anticoagulant stops the sample clotting within the tube.
It is not possible to provide results on haemolysed, or lipaemic samples. These will be rejected with the appropriate comment. Sample tubes that have expired cannot be accepted. Thrombophilia screens cannot be processed if taken during an acute event or if the patient is anticoagulated.
- Coagulation Lab, James Cook University Hospital, Marton Road, TS4 3BW
- Coagulation Lab, Friarage Hospital, Northallerton, DL6 1JG
Should samples require further testing for AT, PC, and PS they will be referred to:
Specialist Haematology Laboratory in Sheffield and Sheffield Molecular Genetics
Please note Factor V Leiden and Prothrombin Gene Mutation have been validated/verified for clinical application, but are currently outside the scope of accreditation pending UKAS inspection.