# Deep Vein Thrombosis

> Deep vein thrombosis for NEET-PG Medicine covering the Wells score, D-dimer logic, compression ultrasound, anticoagulation choice and the duration of treatment.

- Canonical URL: https://prepelephant.com/topics/neet-pg/medicine/deep-vein-thrombosis
- Exam / course: NEET-PG · Subject: Medicine
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-08
- Last updated: 2026-10-08
- Reference basis: Harrison's Principles of Internal Medicine; ESC Guidelines on acute pulmonary embolism; Bailey and Love's Short Practice of Surgery
- How to cite: "Deep Vein Thrombosis", PrepElephant, https://prepelephant.com/topics/neet-pg/medicine/deep-vein-thrombosis

## Direct answer

Deep vein thrombosis is thrombus formation in the deep veins of the leg or pelvis, most often the calf and proximal veins. It is assessed with the Wells score, D-dimer and compression ultrasonography. A low Wells score with a negative D-dimer excludes it, a likely score goes directly to ultrasound, and a confirmed thrombus is treated with a DOAC or low-molecular-weight heparin, with duration set by whether a reversible risk factor provoked the event.

## What you must remember

- **Wells score for DVT:** active cancer, paralysis or recent plaster cast, bedridden for three days or major surgery within twelve weeks, localised deep vein tenderness, entire leg swollen, calf swelling over 3 cm, pitting oedema, collateral superficial veins and previous DVT each score one; an alternative diagnosis as likely subtracts two; a total of 2 or more means DVT is likely.
- **D-dimer logic:** used only when probability is low, where a negative result excludes DVT; a positive result is non-specific and always needs imaging.
- **Compression ultrasound:** the first-line test; failure of the vein to compress completely under probe pressure is diagnostic.
- **Anticoagulation:** low-molecular-weight heparin or a DOAC; rivaroxaban and apixaban have a short intensified initial phase and need no parenteral bridge.
- **Duration:** three months for a provoked event with a resolved risk factor; extended therapy for unprovoked or recurrent disease; continued while cancer is active in cancer-associated thrombosis.
- **Phlegmasia cerulea dolens:** massive venous obstruction with limb ischaemia and cyanosis, requiring emergency anticoagulation and sometimes thrombectomy.

## A 38-year-old with a swollen left calf after caesarean section

A 38-year-old woman, eleven days after caesarean section, presents with left calf swelling, tenderness and pitting oedema.

1. **Score the probability:** Her Wells score is above 2 because of recent surgery, calf swelling over 3 cm, deep vein tenderness and pitting oedema confined to the leg, so DVT is likely and D-dimer is bypassed.
2. **Image directly:** Compression ultrasound shows a non-compressible femoral vein, which means proximal DVT.
3. **Choose the drug for breastfeeding:** In the puerperium low-molecular-weight heparin is preferred, because DOACs are not recommended in breastfeeding; warfarin, started under heparin cover, is an acceptable alternative and is compatible with breastfeeding.
4. **Set the duration:** The provoking factors are surgery and pregnancy, so the planned duration is three months.
5. **Support and follow up:** Compression stockings give symptom relief rather than routine prevention of post-thrombotic syndrome, and baseline limb measurements help, since post-thrombotic syndrome is judged against the uninvolved leg.
6. **Adjust for calf-vein disease:** If the thrombus were isolated calf-vein thrombosis, symptomatic distal thrombus is anticoagulated, while asymptomatic cases are often followed with repeat ultrasound over about two weeks, per current guidance.

## Where the examiner pulls the trap

The examiner's favourite errors involve the pre-test filter, the D-dimer and the structural cause.

- **Trap:** treating a normal D-dimer as excluding DVT in a likely case — **Correct:** the Wells score is only a pre-test filter, and D-dimer has high negative predictive value only in low-probability patients, so ultrasound is performed directly in likely DVT.
- **Trap:** relying on D-dimer in pregnancy — **Correct:** D-dimer is raised nonspecifically in pregnancy, so ultrasound is the first investigation.
- **Trap:** missing May-Thurner syndrome as a cause of left-sided DVT — **Correct:** compression of the left common iliac vein by the overlying right common iliac artery leads to left-sided DVT, and stenting is considered when symptoms persist.
- **Trap:** using an inferior vena cava filter as routine treatment for proximal DVT — **Correct:** filters are reserved for patients who cannot take anticoagulation.

## Frequently asked questions

### What Wells score threshold separates likely from unlikely DVT?

A Wells score of 2 or more classifies deep vein thrombosis as likely, and compression ultrasound is performed directly. A score of 1 or less classifies it as unlikely, and D-dimer is then used to exclude the diagnosis.

### Why is D-dimer not used when the Wells score is high?

D-dimer has a useful negative predictive value only in low-probability patients, so in likely deep vein thrombosis a normal result cannot rule it out. Compression ultrasound is therefore performed directly in these patients.

### What is the first-line investigation for suspected deep vein thrombosis?

Compression ultrasonography of the leg veins is the first-line investigation for suspected deep vein thrombosis. Failure of the vein to compress fully under probe pressure confirms the thrombus.

### How long should anticoagulation continue after a provoked DVT?

Anticoagulation for a provoked deep vein thrombosis is continued for three months, after which it is usually stopped if the provoking factor has resolved. Unprovoked or recurrent events prompt extended therapy.