D-dimer

D-dimer is a scrap left over when your body breaks down a blood clot. An enzyme called plasmin chops up stabilized fibrin, the clot's mesh. D-dimer is the debris. So it acts as a general sign that your clotting system has been active. Labs measure it by immunoturbidimetric or ELISA assays, in FEU or DDU units. Its main job is to rule out a clot (venous thromboembolism). A low value (often under 500 ng/mL FEU), plus a low pre-test risk, has a negative predictive value above 95%. In plain terms, a clot is very unlikely. The ADJUST-PE study (Righini 2014) set an age-adjusted cutoff for patients over 50: your age × 10 ng/mL FEU. That safely improves accuracy in older adults. But D-dimer also rises with age, pregnancy, inflammation, surgery, injury, cancer, sepsis, and severe liver or kidney disease. So a high value is non-specific. You must read it alongside imaging.

Last reviewed: June 22, 2026

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