D-Dimer

Also known as: Fibrin split products, FDP, Fibrin degradation products

D-dimer is a fibrin degradation product released when a blood clot dissolves. It is primarily used as a rule-out test for deep vein thrombosis (DVT) and pulmonary embolism (PE) — a low result in a low-risk patient effectively excludes these diagnoses.

Specimen

Venous blood (citrate or serum — lab dependent)

Turnaround

1–2 hours

Fasting

Not required

Reference Ranges

Measurement	Reference Range	Unit	Note
Normal	≤ 500	ng/mL FEU	Age-adjusted cut-off: age × 10 ng/mL for patients over 50

Reference ranges are typical adult values. Your laboratory may use slightly different intervals — always use your lab's reported reference.

What This Test Measures

When a clot forms, the coagulation cascade produces cross-linked fibrin. As the body dissolves (lyses) the clot, plasmin breaks fibrin into fragments including D-dimer — so named for two D domains of fibrin linked together. D-dimer is not produced unless clotting has occurred. However, many non-thrombotic conditions also activate coagulation, making D-dimer highly sensitive but poorly specific.

When Is This Test Ordered?

Ruling out DVT or PE in low-to-moderate pre-test probability patients
Diagnosing disseminated intravascular coagulation (DIC)
Monitoring COVID-19 coagulopathy severity
Post-PE follow-up to guide duration of anticoagulation

When Results Are High

Elevated D-dimer does not diagnose DVT or PE — it only prompts imaging. Many conditions raise D-dimer: infection, malignancy, surgery, pregnancy, trauma, AF, and age. A D-dimer above the age-adjusted cut-off in a high-risk patient warrants CT pulmonary angiography (CTPA) or lower limb Doppler ultrasound.

When Results Are Low

A normal D-dimer in a low-risk patient (Wells score 0–1 for PE, or 0 for DVT) has a negative predictive value above 99% — effectively ruling out significant thrombosis without imaging. This is its primary clinical value: a rule-out tool, not a rule-in tool.

Factors That Can Affect Your Result

Pregnancy raises D-dimer progressively through each trimester — use pregnancy-specific cut-offs
Age — use age × 10 ng/mL as the cut-off for patients over 50 (YEARS algorithm)
Malignancy significantly raises D-dimer, limiting its negative predictive value
Recent surgery, trauma, or infection invalidates D-dimer as a VTE rule-out

Tracking This Test Over Time

D-dimer is a rule-out tool, not a monitoring tool. In most contexts, serial D-dimer testing during anticoagulation does not guide management. However, a persistently elevated D-dimer after completing anticoagulation for unprovoked PE may support prolonged anticoagulation in some risk-stratification algorithms.

Track your D-Dimer in Looms

Related Tests

PT / INR

Prothrombin time measures how long blood takes to form a clot via the extrinsic coagulation pathway. The INR standardises PT results across laboratories and is essential for monitoring warfarin therapy.

Medical disclaimer

This page is for educational purposes only and does not constitute medical advice. Reference ranges vary between laboratories, and results must be interpreted in the context of your symptoms, history, and other tests. Always discuss your results with your healthcare provider. Content reviewed by the Looms medical team, 2026-06-01.

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