What is this test?
D-dimer is a fragment produced when cross-linked fibrin is broken down. In people with an appropriate low or intermediate clinical probability, a negative result can help rule out venous thromboembolism; a raised result is nonspecific.
Why might it be ordered?
- To help assess possible deep-vein thrombosis or pulmonary embolism within a clinical decision pathway.
- To assess clotting activation in other carefully selected situations.
What sample is needed?
A blood sample is required. The laboratory chooses the correct tube and handles the sample for this test.
How should you prepare?
No special fasting is usually needed. Acute one-sided leg swelling, sudden breathlessness, chest pain, coughing blood, fainting or severe symptoms require urgent medical assessment rather than self-ordering or waiting for a result.
How should you understand the result?
A raised D-dimer does not diagnose a clot and can occur with age, pregnancy, infection, inflammation, cancer, surgery or injury. Imaging and clinical probability determine the next step.
Sources and editorial status
This patient-facing text is an editorial draft. It should be approved by a laboratory physician before official publication.