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>Guidelines for Thrombophilia Screening in Patients Taking Oral Contraceptives

Definition

The term Thrombophilia describes the familial or acquired disorders of the haemostatic mechanism which are likely to predispose to thrombosis.

Recent developments

Evidence has become available recently that some oral contraceptives are more likely to predispose to thrombosis. Although no national guidelines have been produced, suggestions have been made on the media that women concerned about their risk of thrombosis could have a Thrombophilia screen performed.

Patients who should be investigated for Thrombophilia

The Haemostasis and Thrombosis task Force of the British Committee for Standards in the Haematology have issued guidelines as to which patients should be investigated.

The first six conditions listed would probably not be applicable to patients that you were considering starting on an oral contraceptive but the last four conditions may be relevant.

* These patients may need to be investigated for familial thrombophilia (see below)
** These patients may need to be investigated for evidence of the antiphospholipid syndrome.

Familial Thrombophilia

The tests normally performed are:

Except in very unusual cases such patients do not need to be tested for the presence of antiphospholipid antibodies or the lupus anticoagulant.

Activated Protein C resistance

In the last few years this has emerged as the commonest cause of familial thrombophilia. It is present in 3-5% of a general population sample in the Netherlands but the incidence in the UK may be less. It is claimed that women who use oral contraceptive and who have activated protein C resistance may be 30 times more likely to suffer thromboembolism than in who do not have the abnormality and who are not on oral contraceptive

The most common cause of activated protein C resistance is factor V Leiden.

Screening for Antiphospholipid Antibodies

Citrated blood is tested for the presence of the lupus anticoagulant. Clotted blood is used for measurement of antiphospholipid antibody.

Except in very unusual circumstances these patients do not need to be tested for familial thrombophilia.

Thrombophilia screening tests cannot be done on blood taken at the surgery, but there is no need for a formal referral to Haematology Outpatients.
  • Phone ext 3721, give patient details, ask for date and time for patient to attend Path Lab.
  • Send patient to Path Lab with a request form marked "Thrombophilia Screen"

PLEASE NOTE:

  • Thrombophilia screen results are uninterpretable in pregnant women and in anticoagulated patients.
  • Patients arriving without being booked may have to wait a long time. The lab staff are busy!
  • Results will come back piecemeal. FBC, coagulation screen and DRVVT will be rapid-return from Wansbeck. Protein C, Protein S, Antithrombin III, Activated Protein C Resistance/Factor V Leiden and Anticardiolipin Antibodies go to Newcastle, so turnaround is much slower.
  • Abnormal results will have an interpretative comment.

Causes of thrombophilia

Hereditable thrombophilia

  Increased risk of thrombosis Prevalence in patients with venous thromboembolism (VTE) (%) Prevalence in normal population (%)
Factor V Leiden heterozygous (activated protein C resistance)
Factor V Leiden homozygous individuals have 80x risk of VTE		 3-8x 25-50 5.0
Prothrombin G20210A 3x 6 2.0
Antithrombin deficiency 25-50x 1 0.02
Protein C deficiency 10-15x 3 0.3
Protein S deficiciency 10x 3 2.0
Dysfibrinogeariablenaemia Variable Low Rare

Acquired thrombophilia

Source

Mo Dewar, consultant haemotologist. BHF Factfile 02/2002

References