Screening for a prothrombotic diathesis in patients attending family planning clinics

1. To determine the frequency of prothrombotic markers in young women seeking a new or a repeat prescription of the oral contraceptive pill and perceived to be at high risk of thrombosis. 2. To assess cost-effectiveness of thrombophilia testing within this population. 3. To determine the frequency of acquired activated protein C (APC) resistance.

Results of thrombophilia testing were retrospectively reviewed on 220 consecutively referred patients' plasmas. Women tested were clients attending local family planning clinics for a new or repeat contraceptive prescription. Samples for testing were collected by the Community Laboratory Service. Investigations included: antithrombin III (AT III), protein C, protein S, APC resistance, factor V Leiden mutation analysis and anti-cardiolipin antibodies.

Abnormalities were detected in 35 (15.9%) of the 220 women tested. No patient had all tests performed. The most frequently detected abnormality was an increased APC resistance in 6.8% of the women tested. Three of the 13 patients with an abnormal APC resistance had a discrepancy between the low APC ratio and a negative mutation analysis result for factor V Leiden, suggesting acquired APC resistance. Deficiency of protein C was found in 1.2% (of 162), protein S in 2.0% (of 140), antithrombin III in 0.6% (of 159). Low-titre anti-cardiolipin antibodies were detected in 13.9% of this group (115 tested).

The frequency of abnormal thrombophilia markers detected in this cohort of young women is not significantly different from that seen in a control population. This low incidence suggests that testing has been applied on a population screening basis, rather than preselecting a high-risk group. Thrombophilia screening in this patient group cannot be justified when the clinically relevant end-point is death from pulmonary embolism. The cost of preventing one fatal pulmonary embolism arising as a consequence of screening for activated protein C resistance due to the commonly occurring factor V Leiden is a minimum $25,000,000. This compares very unfavourably with the estimated cost per life saved in the National Breast Screening Programme.