D-dimer

Units and thresholds differ between assays (FEU and D-dimer units are not interchangeable, and some laboratories report in mg/L), and in the general population the value rises steadily with age, so many laboratories quote an age-adjusted threshold above 50 years; use the range your lab printed.

D-dimer is a fragment released when a blood clot is broken down by the body. Some clotting and clot breakdown goes on all the time, so a small amount is always present. A higher level shows that more clot than usual has formed and been dissolved somewhere in the body, but does not say where or why.

Doctors request it mainly when they are looking into a possible clot in the leg or lung, where a low result is helpful. It is also used in severe illness where clotting is being activated throughout the body, and in some infections including COVID-19.

• Blood clots in the veins of the legs or lungs
• Infection, inflammation and severe illness of any kind
• Recent surgery, injury or bleeding
• Pregnancy and the weeks after childbirth
• Cancer
• Older age
• Liver and kidney disease
• Heart disease, including heart failure and atrial fibrillation

• A low value is the usual finding in the general population and is not a cause for concern
• Anticoagulant medicines lower it

• It rises steadily with age in the general population, which is why many laboratories use an age-adjusted threshold over 50
• Pregnancy raises it as an expected change, often above the printed range by the third trimester
• Any recent infection, operation, injury or long journey raises it
• Different assays report in different units and are not comparable with one another

No fasting needed. Citrate tube. It is interpreted in the setting in which it was taken and is rarely useful as a routine or repeated test.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.