MedSysEvidence-graded reference

MedSys / Pulmonary embolism

Pulmonary embolism

Eight chapters. A clot that has travelled to the lung: how to recognise it, what the hospital should do and how quickly, how it is treated, and the months afterwards — when the work of stopping the next one is done.

All chapters For doctors Printable checklist

A pulmonary embolism (PE) is a blood clot that has lodged in one of the arteries of the lung. It almost always starts somewhere else — usually a deep vein in the leg or pelvis — breaks free, travels through the heart, and stops where the lung's arteries narrow. Small ones are survivable and common. Large ones can stop the heart within minutes. The difference between the two is mostly size and luck, which is why the treatment for both is urgent.

The three things that matter most. Sudden breathlessness with no obvious reason is a 999 call, not a GP appointment — especially with chest pain that is worse on breathing in, a fast pulse, coughing blood, or a swollen or painful calf. Treatment should start before the scan is done if the scan will take more than four hours. And the three-month review after a PE is where the next one gets prevented; make sure it happens.

1. What it feels like

The textbook picture is breathlessness that came on over minutes, a sharp pain in the chest or side that is worse when you breathe in, and a fast heartbeat. Some people cough up blood. Some faint. Around half have a leg that is swollen, warm or aching — the deep vein thrombosis (DVT) the clot came from.

The dangerous versions are the quiet ones. Breathlessness on its own, that a person puts down to being unfit. A fast pulse and nothing else. A collapse with no warning. Unusual anxiety with a feeling of not getting enough air. These get attributed to a chest infection, a panic attack or a pulled muscle, and the clot is found days later or not at all. The recognising-it chapter goes through each of them.

Who it happens to. Anyone, but the risk climbs sharply after surgery, a hospital stay, a broken leg, a long period in bed or a chair, cancer, pregnancy and the weeks after birth, the combined pill or HRT, and a previous clot. Around one in three has no obvious trigger at all, and that group needs the most careful follow-up.

2. What should happen in hospital

  1. A structured assessment, not a guess

    The clinician scores how likely a PE is (the Wells score). A "likely" score goes straight to a scan. An "unlikely" score gets a blood test called D-dimer first; if it is normal, PE is effectively ruled out and no scan is needed.

  2. The scan, within four hours if possible

    Usually a CT pulmonary angiogram (CTPA): a CT scan of the chest with dye in the blood, which shows the clot directly. A lung ventilation-perfusion scan is the alternative when contrast dye or radiation is a problem. If the scan cannot happen within four hours, an anticoagulant should be started while you wait.

  3. A blood panel, an ECG and a chest X-ray

    Full blood count, kidney and liver function, clotting tests, and usually troponin and BNP, two blood markers of strain on the heart. These decide how sick you are, not whether you have a clot.

  4. A decision about how serious it is

    Most PEs are "low risk": blood pressure normal, heart coping. Many of those people go home the same day on tablets. A minority are "high risk", with a struggling heart and falling blood pressure, and get clot-busting drugs. In between is the group where 2026 changed the argument — see the treatment chapter.

  5. An anticoagulant, usually a tablet

    In the UK the first choices are apixaban or rivaroxaban, started on the day of diagnosis and continued for at least three months. They do not dissolve the clot; they stop it growing and stop new ones forming while the body clears it.

The hospital checklist chapter lists every test with the time limit NICE sets, and the printable version fits on one sheet.

3. The months after

At three months (three to six with cancer) there should be a review, and it is a real decision: stop the anticoagulant, or continue it. If the clot had a clear one-off cause that has gone — an operation, a leg in plaster — stopping is usually right. If it had no cause, most people are advised to continue, often for years, because the chance of another is high and the tablets are safer than they used to be. That decision should be made with you, and it should be reviewed every year.

The same review is when a cause should be looked for. What that means in practice is narrower than people expect: a proper examination and the routine bloods, not a scan of the whole body. Genetic clotting tests are only worth doing when the answer would change the decision to stop treatment. The after-hospital chapter explains why.

One thing to raise yourself. Around one person in three is still short of breath or tired months after a PE. Most of that is deconditioning and recovers. A small number — about 3 in 100 — develop a chronic form where old clot scars the lung's arteries and raises the pressure in them. It is treatable, and the test for it is a heart ultrasound. If you are still breathless at three to six months, ask for one.

4. Where UK and US guidance differ

Both agree on the tablets, the scan and the three-month review. They part company in the middle of the severity range. In March 2026 the US cardiology societies published a guideline that opened catheter treatment — threading a tube into the lung artery to dissolve or remove the clot — to patients whose blood pressure is holding but whose heart is under strain, and two trials that year showed it cut early deterioration. NICE's guidance in the UK still says no clot-busting unless blood pressure has collapsed. That is not carelessness on NICE's part: the trials are new and neither showed a survival benefit. But if you or a relative are in that middle group, it is a reasonable thing to ask about, and the treatment chapter gives you the numbers to ask with.