Calf pain and deep vein thrombosis (DVT)
Wells score first. "Likely" means an ultrasound; "unlikely" means a D-dimer. Start anticoagulation if the scan will be delayed.
A 46-year-old woman has a painful, swollen left calf for 3 days. Last week she travelled 14 hours by bus from Karachi to Lahore. She takes the combined pill. The left calf is 4 cm bigger than the right (measured 10 cm below the tibial tuberosity) with pitting oedema and tenderness along the deep veins. Pulse 88, SpO₂ 98%, no breathlessness. Ultrasound isn't available until tomorrow morning.
What is her Wells score, do you start treatment tonight, and which drug?
- Ask about breathlessness, chest pain, haemoptysisPulmonary embolism changes everything: see the PE guide.
- Look at the whole legMassive swelling with a blue or white leg is limb-threatening.
- Wells score firstIt decides D-dimer or straight to scan.
- DVT likely (2 or more)Compression ultrasound within 4 hours.
- DVT unlikely (1 or less)D-dimer. Negative excludes DVT. Positive needs a scan.
- Scan delayedStart anticoagulation and scan within 24 hours.
- Bloods before anticoagulationCBC, creatinine, LFTs, clotting.
- Confirmed DVTDOAC for at least 3 months. Look for the cause.
- Breathlessness, chest pain, haemoptysis or low SpO₂
- Massive swelling, blue or white leg
- Pregnant or recently delivered
- Active cancer
- Active bleeding or high bleeding risk
- Poor kidney function (choice and dose of drug)
- Pulmonary embolism
- Phlegmasia (limb-threatening DVT)
- Cellulitis
- Ruptured Baker's cyst
- Calf muscle tear
- Compartment syndrome
- Underlying cancer
| Wells: DVT likely | 2 points or more |
| Ultrasound | Within 4 hours if likely, otherwise interim anticoagulation and scan within 24 hours |
| Apixaban | 10 mg twice daily for 7 days, then 5 mg twice daily |
| Rivaroxaban | 15 mg twice daily for 21 days, then 20 mg once daily with food |
| Enoxaparin | 1.5 mg/kg once daily or 1 mg/kg twice daily |
| Duration | At least 3 months, longer if unprovoked or ongoing risk |
| Negative scan but Wells likely | Repeat scan in 6–8 days, or D-dimer to decide |
Check every dose against a current drug reference and your hospital protocol.
On this page
What is a DVT?
A clot in the deep veins of the leg (calf, popliteal, femoral, iliac). Proximal DVT (popliteal and above) carries the highest risk of pulmonary embolism. Distal (calf-only) DVT is less dangerous but can extend.
Virchow's triad explains the risk:
- Slow flow: immobility, long travel, paralysis, plaster.
- Vessel damage: surgery, trauma, previous DVT, IV drug injection into the groin.
- Sticky blood: cancer, pregnancy and the postpartum period, oestrogen (pill, HRT), dehydration, thrombophilia, nephrotic syndrome, inflammatory bowel disease.
History
- When did it start? Sudden or gradual? One leg or both?
- PE symptoms: breathlessness, pleuritic chest pain, haemoptysis, collapse.
- Risk factors: surgery in the last 12 weeks, bed rest over 3 days, plaster, long travel, cancer (known or symptoms like weight loss), pregnancy or recent delivery, pill or HRT, previous clot, family history.
- Bleeding risk before anticoagulation: ulcers, recent bleeding, falls, liver disease, kidney disease, low platelets, alcohol.
- Drugs: enzyme inducers (carbamazepine, rifampicin) and some HIV drugs interact with DOACs.
Examination
- Measure both calves 10 cm below the tibial tuberosity. A difference of 3 cm or more scores a Wells point.
- Pitting oedema, tenderness along the deep veins, visible superficial (collateral) veins, swelling of the whole leg.
- Colour and temperature: red and hot (cellulitis), blue and very swollen (phlegmasia cerulea dolens), white (phlegmasia alba dolens).
- Behind the knee: Baker's cyst.
- Chest, pulse, SpO₂, RR for PE.
Two-level Wells score for DVT
| Feature | Points |
|---|---|
| Active cancer (treatment within 6 months or palliative) | 1 |
| Paralysis, paresis or recent plaster on the leg | 1 |
| Bedridden for 3 days or more, or major surgery within 12 weeks | 1 |
| Tenderness along the deep venous system | 1 |
| Entire leg swollen | 1 |
| Calf swelling 3 cm or more compared with the other leg | 1 |
| Pitting oedema in the symptomatic leg | 1 |
| Collateral superficial veins (not varicose) | 1 |
| Previously documented DVT | 1 |
| An alternative diagnosis at least as likely | −2 |
Use the Wells DVT calculator.
The pathway
- Proximal leg ultrasound within 4 hours
- If not possible, D-dimer and interim anticoagulation, scan within 24 hours
- Negative scan with positive D-dimer: repeat scan in 6–8 days
- D-dimer
- Negative: DVT excluded, look for another cause
- Positive: ultrasound within 4 hours or interim anticoagulation
Wells first, then D-dimer only if DVT is "unlikely". D-dimer rises with age, pregnancy, infection, cancer and after surgery, so a positive D-dimer on its own proves nothing.
Differential diagnosis
| Condition | Clues |
|---|---|
| Cellulitis | Red, hot, spreading edge, fever, entry point. Can coexist with DVT |
| Ruptured Baker's cyst | Knee arthritis, sudden calf pain, bruising around the ankle |
| Calf muscle tear | During exercise, sudden pain, localised tenderness |
| Superficial thrombophlebitis | Tender, red cord along a superficial vein |
| Lymphoedema or venous insufficiency | Both legs, chronic, skin changes |
| Heart, liver or kidney failure, low albumin | Both legs swollen |
| Drug oedema | Amlodipine, nifedipine, both ankles |
| Compartment syndrome | After injury, severe pain on passive stretch |
Investigations
| Test | Why |
|---|---|
| Compression ultrasound (proximal) | Diagnosis |
| D-dimer | Only if Wells "unlikely" |
| CBC | Platelets before anticoagulation |
| Creatinine (eGFR) | Choice and dose of anticoagulant |
| LFTs, clotting (PT, APTT) | Bleeding risk, baseline |
| Urine dipstick | Protein (nephrotic syndrome) |
| Pregnancy test | Women of reproductive age (changes the drug) |
| Further cancer tests | Only if history or examination suggests cancer |
Treatment
- Start anticoagulationDOAC first choice unless contraindicated.
- Check bleeding risk and kidney functionChoose the drug and dose.
- ExplainWhy, how long, side effects, bleeding warning signs, interactions.
- Duration3 months if provoked by a temporary cause. Longer if unprovoked, cancer or ongoing risk.
- Review at 3 monthsStop or continue.
- Calf-only DVT: treat if symptomatic or high risk; otherwise some centres repeat the scan in a week to look for extension.
- Compression stockings don't prevent post-thrombotic syndrome and aren't routine.
- Mobilise. Bed rest doesn't help.
- Choose a drug the patient can afford and take reliably. In Pakistan, cost often decides between a DOAC and warfarin; warfarin needs INR checks the patient can actually reach.
Special situations
- Enoxaparin by weight for the rest of pregnancy and at least 6 weeks postpartum (3 months total minimum)
- No DOAC or warfarin in pregnancy
- Obstetric team
- Enoxaparin or a DOAC (apixaban, rivaroxaban, edoxaban) depending on cancer type and bleeding risk
- Oncology advice
- Limb-threatening
- Vascular surgeon now
- Heparin
- Catheter-directed thrombolysis may be considered
- Avoid most DOACs
- Unfractionated heparin or adjusted enoxaparin, then warfarin
- Senior
- IVC filter only if anticoagulation impossible
Common mistakes
- Sending a D-dimer on everyone. In "likely" patients it adds nothing.
- Forgetting to ask about breathlessness and chest pain.
- Not starting interim anticoagulation when the scan is delayed.
- Giving a DOAC without checking kidney function and weight.
- Prescribing a DOAC to a pregnant woman.
- Labelling a red, hot leg as "only cellulitis" without thinking of DVT (or the reverse).
- Discharging without telling the patient how long to take the drug and what bleeding looks like.
Advice for patients
- Take the tablet at the same times every day. Don't stop early.
- Come back at once with sudden breathlessness, chest pain, coughing blood, bleeding that won't stop, black stools, vomiting blood, or a severe headache.
- Tell any doctor or dentist that you take a blood thinner.
- Avoid NSAIDs (ibuprofen, diclofenac) and herbal products with bleeding risk.
- Women: discuss stopping oestrogen-containing contraception and use another method.
Frequently asked questions
What is the apixaban dose for DVT?
10 mg twice daily for 7 days, then 5 mg twice daily, for at least 3 months.
When is a D-dimer useful in suspected DVT?
Only when DVT is "unlikely" on the Wells score (1 or less). A negative D-dimer then rules out DVT. If DVT is likely, go straight to ultrasound.
Can DVT be treated before the ultrasound?
Yes. If the scan can't be done within 4 hours and DVT is likely, start anticoagulation and scan within 24 hours.
How long is DVT treated?
At least 3 months. Longer (often long term) if there was no clear cause, with cancer, or with ongoing risk.
Which anticoagulant is used for DVT in pregnancy?
Enoxaparin by weight. DOACs and warfarin are not used in pregnancy.
Test yourself
Exam-style questions on this guide, from our two question banks. Choose an answer to see why each option is right or wrong.
1. A patient has a Wells DVT score of 3. What is the next step?
Answer: Leg ultrasound. DVT likely (2 or more): proximal leg ultrasound; anticoagulate while waiting if delayed.
- D-dimer only: For unlikely scores.
- Venography for all: Not first.
- Discharge: No.
- CT pulmonary angiogram: Not without chest symptoms.
2. A patient has Wells score 0 and a negative D-dimer. What does this mean?
Answer: DVT excluded. Unlikely score plus negative D-dimer rules out DVT.
- Start apixaban: No.
- Ultrasound still needed: Not required.
- Repeat D-dimer weekly: No.
- Venography: No.
3. What is the first-week dose of apixaban for DVT?
Answer: 10 mg twice daily. Apixaban 10 mg twice daily for 7 days, then 5 mg twice daily.
- 15 mg twice daily: Rivaroxaban loading.
- 2.5 mg twice daily: Prevention dose.
- 5 mg once daily: Too low.
- 20 mg once daily: Rivaroxaban maintenance.
4. A 45-year-old has a unilateral swollen calf 3 cm larger than the other, pitting oedema and recent long-haul travel; two-level Wells score is ‘likely’. What is the next step?
Answer: Proximal leg vein ultrasound. Suspected DVT: two-level Wells score. ‘Likely’ (≥ 2) → proximal leg vein ultrasound within 4 hours (interim anticoagulation if delayed); if negative, D-dimer — positive → repeat scan in 6–8 days. ‘Unlikely’ → D-dimer; negative excludes DVT, positive → ultrasound. D-dimer is sensitive but non-specific (raised in pregnancy, infection, cancer, surgery, age). Treatment: DOAC (apixaban/rivaroxaban) for ≥ 3 months for provoked DVT.
- D-dimer only and discharge if positive: A positive D-dimer does not allow discharge.
- CT pulmonary angiogram: There are no PE symptoms.
- Venography as first-line: Venography is invasive.
5. A 50-year-old has a proximal DVT 3 weeks after knee arthroscopy (provoked). Renal function is normal. What is the treatment and duration?
Answer: DOAC for 3 months. Proximal DVT: confirm with compression ultrasound (Wells score + D-dimer guide). Treat with a DOAC (apixaban, rivaroxaban) or LMWH → warfarin. Provoked (surgery, trauma, immobility) → 3 months. Unprovoked → consider extended anticoagulation balancing bleeding risk. Cancer-associated → DOAC/LMWH ≥ 6 months. IVC filter only if anticoagulation contraindicated. Compression stockings for symptoms.
- Lifelong warfarin: Lifelong treatment is not needed for a provoked DVT.
- Aspirin only: Aspirin is not adequate.
- IVC filter for all: A filter is only for contraindication to anticoagulation.
6. In Virchow's triad, which factor is most important for thrombosis in arteries and the heart?
Answer: Endothelial injury. Virchow's triad: endothelial injury, abnormal flow (stasis or turbulence) and hypercoagulability. Endothelial injury is dominant in the heart and arteries (atherosclerotic plaque rupture, myocardial infarction, vasculitis). Stasis is most important in veins (DVT).
- Stasis of blood: Dominant in venous thrombosis.
- Hypercoagulability: Important in inherited conditions (factor V Leiden).
- Raised haematocrit: A contributor to hyperviscosity.
- Low platelet count: Causes bleeding, not thrombosis.
7. Why are newborn babies given vitamin K at birth?
Answer: Low vitamin K stores and intake. Little vitamin K crosses the placenta, the newborn gut has no bacteria to make it, and breast milk contains little. Without supplements, factors II, VII, IX and X are low, causing vitamin K deficiency bleeding (haemorrhagic disease of the newborn). A single IM dose at birth prevents it.
- To prevent neonatal jaundice: Not related.
- To prevent rickets: Vitamin D prevents rickets.
- To prevent neonatal hypoglycaemia: Not its role.
- To prevent anaemia of prematurity: Hypoglycaemia is prevented by early feeding, not vitamin K.
References and dose sources
- NICE NG158 — Venous thromboembolic diseases
- Apixaban dosing: Drugs.com: Apixaban dosage (see also our apixaban dose page)
- Rivaroxaban dosing: Drugs.com: Rivaroxaban dosage (see also our rivaroxaban dose page)
- Enoxaparin dosing: Drugs.com: Enoxaparin dosage (see also our enoxaparin dose page)
- Warfarin dosing: Drugs.com: Warfarin dosage (see also our warfarin dose page)
International guidance is linked where it reflects good practice. Where your hospital’s protocol differs, follow your hospital.