How the test is used
If your doctor thinks a clot is unlikely, a normal D-dimer can safely rule it out without a scan. That is its main strength — it is good at ruling clots out, not at ruling them in.
A raised D-dimer is non-specific: it goes up with clots but also with infection, inflammation, recent surgery, pregnancy and increasing age. So a positive result usually leads to a scan (such as a leg ultrasound or a CT of the lungs) rather than a diagnosis on its own.
Common questions
Does a positive D-dimer mean I have a clot?
No. It means a clot cannot be ruled out by the test, so imaging is usually arranged. Many people with a raised D-dimer do not have a clot.
Is the D-dimer used in everyone with suspected clots?
It is most useful in people assessed as low or moderate risk. In high-risk patients, doctors often go straight to a scan rather than relying on the D-dimer.
Related tools
These calculators are designed for healthcare professionals.