Thrombophilia Screen

General Information

Note: For external requests please click Here for Coagulation Disorders request form. Please complete all information fully. Samples for Factor V Leiden and/or Prothrombin G20210A should be sent directly to Heartlands Hospital (the assay is NOT performed at Queen Elizabeth Hospital). These should be refrigerated and then sent at ambient temperature packaged separately from any frozen samples (samples stored in this way are viable for up to 4 weeks).

Samples that meet the following criteria will not be processed:

• Haemolysed, clotted, underfilled or overfilled samples.
• Samples >12 hours old from the time of collection.
• Samples received from other hospital laboratories that have been frozen and thawed.
• Samples which fail the minimum data set.

Assay limitations:

• Antithrombin: not affected by Heparin (UF/LMWH) up to 4U/mL, alpha-1antitrypsin up to 4mg/mL, Heparin Cofactor II up to 4U/mL, Haemoglobin up to 500mg/dL, Bilirubin up to 40mg/dL and triglycerides up to 2300mg/dL.
• Protein C: not affected by Heparin (UF/LMWH) up to 2.0 U/mL, Haemoglobin up to 200mg/dL, Bilirubin up to 21mg/dL.
• Protein S: not affected by Heparin (UF/LMWH) up to 1.5 U/mL, Haemoglobin up to 200mg/dL, Bilirubin up to 25mg/dL.Lipaemic and icteric samples may also interfere with the analyser optical reading unit used in the colorimetric assay method.
• Lupus: DRVVT screen and confirm results are not affected by UFH and LMWH concentrations up to 1 IU/mL, Haemoglobin up to 200 mg/dL, Bilirubin up to 10 mg/dL and Triglycerides up to 500 mg/dL
• Vitamin K antagonists can cause false positive or negative LA results; therefore, LA testing is not recommended in patients receiving warfarin.
• Mixing tests are a criterion for LA and improve the specificity. However, they introduce a dilution factor and may make weak LA samples appear negative. In the absence of any other causes of prolonged clotting times, such samples should be considered LA positive if the screen and confirmatory tests on undiluted plasma give positive results.
• DRVVT ratios are prolonged in the presence of direct factor Xa inhibiting anticoagulants. In this case activated charcoal products such as DOAC-Stop can be used to remove the effect of the anticoagulant.

Notes

All requests for Thrombophilia Screening must be approved by a Haematology Consultant prior to sending samples to the laboratory. Please refer to Clinical guideline [NG158]

Please click Here for further information (see section 1.9 for relevant clinical indications).

Note that Lupus can be requested independently to all other assays included in a Thrombophilia Screen.

Current BSH Guidelines on the investigation and management of antiphospholipid syndrome (Arachchillage et al, 2024) recommend that two lupus anticoagulant assays of different principles are used, and individuals are regarded as having lupus if either test is positive. In this case an APTT (using a reagent with proven lupus responsiveness) and a dRVVT assay are performed.