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A 28-year-old woman presents with a swollen, painful left calf. Doppler ultrasound confirms a proximal deep-vein thrombosis. She takes the combined oral contraceptive pill. Her mother had a pulmonary embolism at 38 and a paternal aunt had a DVT in pregnancy. There is no malignancy or recent surgery. She is started on apixaban.
Questions
a) Which inherited thrombophilias are common and lower-risk versus rare and higher-risk? (2 marks) Common lower-risk: factor V Leiden (activated protein C resistance; commonest in Europeans) and prothrombin G20210A. Rare higher-risk: antithrombin, protein C and protein S deficiency (younger, unusual-site thrombosis, warfarin-induced skin necrosis, heparin resistance for antithrombin). b) Give FOUR indications to test this patient for inherited thrombophilia. (2 marks) VTE under 50; VTE on the combined oral contraceptive pill; strong family history of VTE (two affected first-degree relatives); unprovoked VTE in a young woman of reproductive age (relevant for future pregnancy/OCP counselling). c) Outline HOW and WHEN you would perform the thrombophilia screen. (3 marks) Test selectively (not routinely) and TIME it correctly: ideally AFTER the acute event and OFF anticoagulation, because heparin/warfarin lower protein C, protein S and antithrombin assays giving false results. Screen for acquired causes first (exclude antiphospholipid syndrome, malignancy, nephrotic syndrome, pregnancy). Use functional assays for antithrombin, protein C and protein S, the APC-resistance assay, and confirm factor V Leiden and prothrombin G20210A by genetic PCR. Repeat any abnormal result to exclude transient acquired deficiency before labelling inherited. Offer cascade screening and counselling to first-degree relatives. d) How does the management differ for a low-risk versus a high-risk defect, and what is the specific advice for this young woman? (3 marks) A low-risk defect (heterozygous factor V Leiden / prothrombin mutation) does NOT usually change anticoagulation duration beyond standard VTE therapy, and routine testing rarely alters management. A high-risk defect (antithrombin deficiency, homozygous factor V Leiden, double heterozygosity) or recurrent VTE warrants extended / lifelong anticoagulation. For this woman: stop the combined oral contraceptive pill (synergistic VTE risk, around 35-fold in factor V Leiden carriers) and use progestogen-only or non-hormonal contraception. Plan future pregnancies on prophylactic low-molecular-weight heparin (warfarin is teratogenic, DOACs avoided), and continue anticoagulation for at least 6 weeks postpartum.