For nearly everyone a DVT is treated at home with a tablet started the day it is found. The decisions are about the few who need more than that, how long the tablet continues, and the leg in the years afterwards, where the most widely given advice is the one that does not work.
1. The anticoagulant
Apixaban or rivaroxaban, first line, started the same day (NG158 1.3.8), for at least three months (1.3.5). If neither is suitable: low-molecular-weight heparin injections for at least five days then dabigatran or edoxaban, or heparin overlapping with warfarin. The situations that change the choice — reduced kidney function, cancer, triple-positive antiphospholipid syndrome, weight under 50 kg or over 120 kg — are the same as for a pulmonary embolism and are tabled in the PE treatment chapter. So are the doses and the reversal agents, in the PE clinical chapter.
The tablet does not dissolve the clot. It stops it extending and prevents new ones while the body's own system clears it, which takes weeks to months and is often incomplete: a scan at three months frequently still shows old clot, and that is not a failure of treatment. Pain and swelling improve over days to weeks. Walking is encouraged from the first day; bed rest is not part of the treatment.
2. Home or hospital
Home, unless there is a reason not to: a leg so swollen the circulation is threatened, a bleeding risk that needs watching, kidney failure that needs an injection, pain that needs intravenous relief, a social reason, or a pulmonary embolism as well. Someone going home should leave with the first dose taken, written information on the tablet and the symptoms to return with, a contact number, and the date of the three-month review.
3. Who gets more than a tablet
Clot removal through a catheter
For a large clot in the veins of the thigh and pelvis (iliofemoral DVT), a catheter can be threaded into the vein to drip a clot-dissolving drug directly onto it, sometimes with a device to break it up. The aim is not survival, which anticoagulation already secures, but the leg: clearing the clot quickly may spare the valves. The evidence is mixed. CaVenT, a Norwegian trial, found post-thrombotic syndrome at two years in 41% with catheter treatment against 56% without. ATTRACT, the larger American trial, found no difference overall (47% against 48%) with more bleeding, but less severe post-thrombotic syndrome in the subgroup with iliofemoral clot. NICE's position (1.6.1): consider catheter-directed thrombolysis for a symptomatic iliofemoral DVT when symptoms have lasted less than 14 days, the person has good function, a life expectancy of a year or more, and a low bleeding risk. The American guidance is similar but applied more often. If you have a large thigh clot and a swollen, painful leg within two weeks of onset, it is a reasonable thing to ask whether a vascular centre has considered it.
Filters
A cage placed in the main vein of the abdomen to catch clot before it reaches the lung. NICE (1.7.1–1.7.4) allows one only when anticoagulation is contraindicated (usually active bleeding) or a pulmonary embolism has happened despite anticoagulation after adherence and dosing have been checked, and requires a written plan to remove it as soon as anticoagulation is established. A filter is not a treatment for the clot in the leg, and a filter left in becomes a site for new clots.
4. How long
Three months is the treatment. What happens after is a decision made at the three-month review: stop if the clot was provoked by a trigger that has gone; consider continuing, often for years, if it was unprovoked, because the recurrence risk is high and the tablets are safe. A DVT and a PE are treated identically here, so the review, the reduced-dose option after six months, the cancer search, the thrombophilia and genetic testing rules, and the annual review are all in the PE after-hospital chapter. One addition for a DVT: a clot below the knee, if it is treated at all, is usually treated for six weeks to three months rather than longer.
The full list of tests after a clot — the baseline bloods, the three-month cancer assessment, every thrombophilia and genetic test with what it means and when it is worth doing, and the tests that are sold but useless — is the every-test chapter in the PE topic; it applies unchanged to a DVT.
5. The leg afterwards: post-thrombotic syndrome
A clot damages the one-way valves in the vein. Once the clot has cleared, blood in the leg has to climb against gravity through valves that no longer close, so the leg swells, aches, feels heavy, itches and discolours, and in the worst cases ulcerates at the ankle. Between a fifth and a half of people have some degree of it within two years of a DVT; a severe form affects perhaps one in twenty. It is more likely after a large clot high in the leg, after a second clot in the same leg, with obesity, and when anticoagulation in the first months was inadequate.
| Measure | What the evidence says |
|---|---|
| Compression stockings to prevent it | Do not work. The SOX trial gave 800 people a proper stocking or a placebo stocking for two years and found identical rates. NICE (1.7.5): do not offer them to prevent post-thrombotic syndrome or recurrence |
| Compression for symptoms | Reasonable if a stocking makes the leg feel better; NICE allows it for that purpose and says explain how to wear and replace it (1.7.6) |
| Adequate anticoagulation in the first three months | Sub-therapeutic treatment early on roughly doubles the risk; missed doses matter most here |
| Walking and exercise | Early walking does not increase embolism and reduces symptoms; a walking programme improves the post-thrombotic leg |
| Weight | Obesity is a consistent risk factor for developing it |
| Catheter clot removal | Reduced it in one trial and not the other; a case-by-case decision for large thigh clots (section 3) |
| Elevation, skin care, treating ulcers | Management, not prevention; a leg ulcer clinic is the right place for an established ulcer |
6. What to expect, and when to worry
Improvement in pain and swelling over one to two weeks; some residual swelling for months. Worsening swelling, new pain, a leg that goes cold or blue, or any breathlessness or chest pain in the first weeks means the clot has extended or moved and needs same-day assessment. Bleeding on the tablet — black stools, blood in urine, a nosebleed that will not stop — is a same-day problem too.
7. Where UK and US guidance differ
- Catheter treatment for iliofemoral DVT. UK: consider, with four criteria. US: a similar position used more liberally, particularly for limb-threatening clot.
- Stockings. Both now say not for prevention, on the same trial.
- Calf clots. UK: outside the pathway. US: treat or re-scan (previous chapter).
- The tablets, the duration and the filter rules are the same.