NICE's pathway for a suspected DVT is short, and every step has a time limit. It is written here by recommendation number so that a patient can tell whether it was followed and a clinician can use it as a reminder. The single most common failure is the last step: a normal scan is taken as the end of the matter when the blood test said it was not.
1. History and examination first (1.1.1)
A history of the risk factors and an examination of the leg, to exclude the other causes in the recognising-it chapter. Then the score.
2. The Wells DVT score (1.1.2)
| Feature | Points |
|---|---|
| Active cancer (treatment within 6 months, or palliative) | 1 |
| Paralysis, weakness or recent plaster immobilisation of the leg | 1 |
| Bedridden for 3 days or more, or major surgery within 12 weeks | 1 |
| Localised tenderness along the deep veins | 1 |
| Entire leg swollen | 1 |
| Calf swelling 3 cm or more greater than the other side | 1 |
| Pitting oedema confined to the symptomatic leg | 1 |
| Collateral (non-varicose) superficial veins | 1 |
| Previously documented DVT | 1 |
| An alternative diagnosis at least as likely | −2 |
2 or more: DVT likely. 1 or less: unlikely.
3. DVT likely (1.1.3–1.1.7)
- A proximal leg vein ultrasound with the result within four hours if possible. "Proximal" means the veins from the knee up: NICE's pathway scans those, not the calf.
- If the scan cannot be done within four hours: a D-dimer, then an anticoagulant, and the scan within 24 hours. The blood is taken before the drug because the drug lowers the D-dimer.
- Scan positive: treat (next chapter).
- Scan negative and D-dimer positive: stop the interim anticoagulant, and repeat the ultrasound six to eight days later. If the repeat is positive, treat.
- Scan negative and D-dimer negative: stop the interim anticoagulant, think about the alternatives, and give the person written advice on the symptoms to return with.
4. DVT unlikely (1.1.8–1.1.11)
- A D-dimer with the result within four hours; if that is not possible, an anticoagulant while waiting.
- D-dimer negative: not a DVT. Alternatives, and written safety-netting advice.
- D-dimer positive: a proximal ultrasound within four hours, or an anticoagulant and the scan within 24 hours. Then as above.
5. D-dimer: the two rules (1.1.12–1.1.14)
A laboratory test is preferred; a fully quantitative point-of-care test is acceptable if the laboratory cannot deliver in time. For people over 50, NICE says consider an age-adjusted threshold (age × 10 in ng/mL), which avoids scans in older people without missing clots. D-dimer is raised by infection, surgery, cancer, pregnancy, inflammation and age, so a positive result means "scan", not "clot".
6. The blood tests before the first dose (1.3.4)
Full blood count, kidney and liver function, and clotting (PT and APTT), taken before the first anticoagulant dose but not waited for; the results are reviewed within 24 hours and the drug or dose adjusted if they demand it. If your first dose was delayed until the bloods came back, that was a delay NICE says should not happen.
7. The calf question
NICE's ultrasound stops at the knee because most calf (distal) clots dissolve without treatment and the trial that tested anticoagulating them (CACTUS) found no fewer clots extending or travelling, and more bleeding. Many UK departments nevertheless scan the whole leg, and when a calf clot is found, practice varies: some treat for six weeks to three months, some repeat the scan in a week and treat only if it has grown. The American guidelines allow either approach. What matters for a patient is that a calf clot found on a whole-leg scan is either treated or re-scanned, not simply reported; and that a normal proximal scan with a raised D-dimer is re-scanned a week later, which is where an extending calf clot is caught.
8. Pregnancy
NG158 does not apply in pregnancy. The Royal College of Obstetricians and Gynaecologists pathway is: no D-dimer (it is raised throughout pregnancy); a leg ultrasound for any clinical suspicion; if negative and suspicion persists, a repeat at days three and seven; and treatment with weight-based low-molecular-weight heparin injections, not tablets, continued for the rest of the pregnancy and six weeks after birth. Pelvic vein clots are commoner in pregnancy and harder to see on ultrasound, so MR venography is used when the leg scan is negative but the picture is convincing.
9. What a negative result should come with (1.1.7)
Being told it is unlikely to be a DVT should come with what to watch for and where to go if it changes. If you leave with only "it's not a clot", ask.
10. Where UK and US guidance differ
- Which veins are scanned. NICE: proximal only, with the repeat scan as the safety net. US practice: commonly whole-leg, with either treatment or serial scanning of calf clots.
- Calf clots. UK: not part of the pathway; treated or re-scanned by local practice. US (CHEST): serial imaging for low-risk distal DVT, anticoagulation for higher-risk or symptomatic ones.
- Everything else — Wells, D-dimer with age adjustment, the four-hour rules, interim anticoagulation — is shared.