Deep Venous Thrombosis on the CCFP exam

Approach

• Use a validated rule, such as the Wells score, to sort the patient into clot likely or clot unlikely.
• Do not trust the exam alone. Only 10 to 20% of people checked for a deep vein clot turn out to have one.
• Clot unlikely: start with a D-dimer, a blood test for clot breakdown.
• Clot likely: go straight to ultrasound of the leg veins.
• In children, the scoring rules and the D-dimer are not proven. Start with ultrasound.

Approach

• If testing is more than 4 hours away and a clot is likely, give a fast-acting anticoagulant now.
• Use a low-molecular-weight heparin injection or a direct oral anticoagulant (DOAC) tablet, such as apixaban or rivaroxaban.
• Hold off if the bleeding risk is high or the drug is not safe for the patient.
• Book the ultrasound as soon as you can, and act on the result.
• Most patients can be treated at home. Admit for a clot that threatens the limb, or a high bleeding risk.

Approach

• High risk: hip or knee replacement, surgery for a hip fracture, and major leg injuries.
• Lower risk, with thinner evidence: knee arthroscopy, amputation and other leg fractures. After amputation, give a heparin injection until discharge.
• After hip or knee replacement or hip fracture, continue for 14 to 35 days, often past discharge.
• Use the long end after a past clot, both joints done, or poor mobility at discharge.
• High bleeding risk: use calf pumps (intermittent pneumatic compression) until an anticoagulant is safe.

Approach

• A positive D-dimer means little. Inflammation, cancer, pregnancy, surgery, a hospital stay, injury and older age all raise it.
• As a first test, a negative D-dimer rules out a clot only when the odds are low. When a clot is likely, use it only after a normal ultrasound.
• A whole-leg scan can over-call small calf clots.
• A clot only in the calf: treat if symptoms are severe or it is likely to spread. Otherwise repeat the scan over 1 to 2 weeks.
• Treat a calf clot if the patient cannot come back for the repeat scan.
• A new clot in the same leg: compare with the old scan. A segment that was normal and now will not squash, or one at least 4 mm wider when squashed, means a new clot.

Approach

• Choose tablets over injections when they work, are safe, and the patient prefers them.
• Check every drug for interactions through the liver enzyme CYP3A4 and the P-glycoprotein pump. Carbamazepine, phenytoin, rifampin and St John's wort lower apixaban levels.
• Warfarin: overlap with heparin for at least 5 days, and until the INR (international normalized ratio) is 2.0 or more on 2 days in a row.
• Check the INR often until it is steady, then every 2 to 4 weeks. Check again after a new drug or an illness.
• On apixaban, no routine clotting tests. Check kidney function at least yearly, more often if it is low.
• Once you start treatment, give it for at least 3 months. A clot provoked by surgery usually needs only 3 months, then stop.
• Teach the signs of bleeding and to take every dose. Ask for news of any new drug or herbal product. On warfarin, keep vitamin K intake steady rather than avoiding it.

Approach

• Do not test after a clot with a clear cause, such as surgery. The result rarely changes care.
• Consider testing, with specialist advice, when a clot has no clear cause or only a weak one.
• An acute clot and warfarin both lower proteins C and S. Tested during either, the levels can read falsely low.
• Results that may change the plan: antiphospholipid syndrome (an immune disorder that causes clots), or a lack of antithrombin, protein C or protein S. These may need lifelong treatment.
• Antiphospholipid syndrome: use warfarin rather than a DOAC.
• One copy of factor V Leiden (a common inherited clotting gene change) or the prothrombin gene change does not change how long to treat. Nor does family history alone.

Approach

• Post-thrombotic syndrome is lasting leg heaviness, pain and swelling after a clot. It follows 20 to 50% of clots.
• Do not prescribe routine stockings to prevent it. A large placebo trial showed no benefit over 2 years.
• Marked swelling from the clot: try stockings for relief. Keep using them as long as they help.
• If you use them, pick knee-length, 20 to 30 mmHg. Without the syndrome, most patients can stop at 6 months; with it, keep them while they help.
• The best prevention is to stop a first clot, and a second one in the same leg, with full treatment.
• Diagnose the syndrome on symptoms, after the first 3 to 6 months. Daily stockings and exercise ease it; diuretics have no proven benefit.