MedSysEvidence-graded reference

MedSys / Blood clots & DVT

Blood clots & DVT

Seven chapters. A clot in a vein, usually a leg: how to recognise it, what should happen and how fast, how it is treated, the leg in the years after, the clots in unusual places, and how they are prevented in the first place.

All chapters For doctors Pulmonary embolism topic Printable checklist

A deep vein thrombosis (DVT) is a clot in one of the deep veins, almost always in a leg, sometimes in an arm. It matters for two reasons. A piece of it can break off and travel to the lung, which is a pulmonary embolism, and that is the reason it is treated urgently. And a clot left in a leg vein damages the vein's valves, so that years later the leg swells, aches and can ulcerate. Both are preventable, and the prevention of the first is the same tablet on the same day.

Three things that matter most. A one-sided swollen, warm or aching calf is a same-day problem, and breathlessness or chest pain with it is 999. The ultrasound should happen within four hours, or an anticoagulant should be started while you wait. And if the first scan is normal but the blood test was raised, there should be a second scan a week later; it is the step most often dropped.

1. Recognising it

Swelling of one calf or one whole leg, warmth, tenderness along the inside of the calf or thigh, reddish or bluish skin, and surface veins that stand out. Usually one side only, usually over hours to a day or two. About half of DVTs cause no symptoms at all and are found only after the piece that broke off reached the lung. The things that mimic it — a torn calf muscle, cellulitis, a ruptured Baker's cyst — are covered in the recognising-it chapter, along with the arm, the skin and the rare sites.

2. What should happen

  1. A score

    The clinician rates how likely a DVT is (the Wells score). Two points or more is "likely".

  2. Likely: a leg ultrasound within four hours

    If it cannot be done in four hours, a D-dimer blood test and an anticoagulant now, and the scan within 24 hours.

  3. Unlikely: a D-dimer within four hours

    Normal, and it is not a DVT. Raised, and the ultrasound follows, with an anticoagulant in the meantime if the scan will take more than four hours.

  4. The repeat scan

    A normal first scan with a raised D-dimer needs a second ultrasound six to eight days later, because a calf clot can grow into the range the scan sees.

  5. Home on tablets

    Apixaban or rivaroxaban, started the same day, for at least three months. Most people never need a hospital bed.

The leg pathway chapter has each step with its NICE recommendation number; the printable checklist puts them on one sheet.

3. Treatment, and the leg afterwards

The anticoagulant does not dissolve the clot; it stops it growing and stops new ones while the body clears it over weeks to months. For a small number of people with a large clot high in the leg, a catheter can be used to break it up; for the very few who cannot take anticoagulants, a filter is placed in the main vein of the abdomen. Between a fifth and a half of people develop the post-thrombotic leg over the next two years. Compression stockings do not prevent it, whatever you were told; walking, weight and treating the clot properly are what count. The treatment chapter has the numbers.

Everything else — which tablet, the three-month review where continuing or stopping is decided, the search for a cause, cancer and genetic testing, travel, contraception and pregnancy — is the same for a DVT as for a pulmonary embolism, and it is written once, in the after-hospital and lifestyle chapters of the PE topic.

4. Clots in unusual places

An arm clot, usually around a drip line or in a young athlete who has been overusing the arm. A clot in the veins of the abdomen, which presents as pain and needs a search for its cause. A clot in the veins draining the brain, which presents as a headache that does not behave like a migraine and is treated with an anticoagulant even when it has caused bleeding. And a clot in a surface vein — thrombophlebitis — which is harmless when it is small and far from the deep veins and is a DVT in waiting when it is not. The unusual-sites chapter covers each.

5. Prevention

Most clots that happen in hospital are preventable, and NICE requires every patient admitted to be assessed for the risk on the day they arrive. The prevention is heparin injections, inflatable leg sleeves, or both, continued after some operations for a month. The prevention chapter is written so you can check it happened, and covers travel and hormones.

6. Where UK and US guidance differ

Less than for the other two clot topics. The diagnosis pathway, the tablets and the duration are the same. The US guidelines are more willing to anticoagulate a clot confined to the calf and to use catheter treatment for large thigh clots; the UK position on both is narrower, and the chapters say where.