A d-dimer test measures a fragment left in the blood when the body breaks down a clot. It is a rule-out test, not a rule-in test. Where clinical probability of venous thromboembolism is low, a negative result excludes deep vein thrombosis or pulmonary embolism without imaging. A raised result confirms nothing on its own: pregnancy, surgery, infection, cancer and age all push D-dimer up. World Thrombosis Day, 13 October, is a fair moment to check it is used that way round.
What does a d-dimer test measure?
D-dimer is “a byproduct of the blood clotting and breakdown process”, formed when plasmin degrades fibrin, with a plasma half-life of six to eight hours (StatPearls, NCBI Bookshelf). A normal result is usually given as below 500 ng/mL, or 0.50 µg/mL.
Treat that figure with care. No universal international standard or calibrator exists for D-dimer, so units and cutoffs differ between assays. Report against your own platform’s validated cutoff.
When does a negative result rule out a clot?
Only when clinical probability came first. The American Society of Hematology puts it plainly: a D-dimer test “is the best first step to check for VTE in patients with low pre-test probability”, and “if results are negative, no further testing is required” (ASH, 2018 VTE diagnosis guideline snapshot).
Roche describes a negative result on its point-of-care assay as “an indication that these diseases can be ruled out with high probability” (Roche CARDIAC D-Dimer). Where suspicion is high, the test does not replace imaging.
Why does a raised d-dimer not mean thrombosis?
The test has high sensitivity and low specificity, which gives it a strong negative predictive value and a weak positive one.
“Pregnancy, trauma, malignancy, surgery, and liver disease can all cause elevations of the D-dimer”, alongside infection, inflammation, immobilisation, smoking, heart failure, cirrhosis and older age. StatPearls is blunt about the consequence: “The D-dimer alone is a dubious marker of clotting in the setting of inflammation, ischemia, infarction, and infection.”
In patients over 50, an age-adjusted cutoff of age in years multiplied by 10 ng/mL improves specificity. American and European colleges support it, but it is not FDA-approved (StatPearls).
Which patients should be assessed before the test is ordered?
The ones already in your wards. World Thrombosis Day puts the burden at one in four deaths worldwide from conditions caused by thrombosis, and reports that 60% of venous clots occur during or after hospitalisation (World Thrombosis Day).
Nigerian audit data suggests assessment is the gap. In a quality improvement project at a Lagos cardiac centre, no admitted patient had VTE risk assessed in the first cycle, while retrospective Caprini scoring found 88% of them were at risk (PMC).
Symptoms will not fill that gap. About half of people with DVT have none at all. When they appear, look for swelling, pain or tenderness, warmth and discolouration in a limb. For pulmonary embolism: difficulty breathing, chest pain worse on a deep breath or cough, a fast or irregular heartbeat, coughing blood, or fainting (CDC). Suspected PE is an emergency.
Where is d-dimer run in a Nigerian laboratory?
Two routes: as a quantitative immunoassay on a laboratory analyser, or at the bedside. The cobas h 232 cardiac marker reader runs Roche CARDIAC D-Dimer on heparinised venous blood, indicated “as an aid in diagnosis when deep venous thrombosis and pulmonary embolism is suspected”. That suits an emergency room with no centrifuge or courier in the path.
One distinction worth putting in writing: PT/INR and aPTT on a meter such as the CoaguChek Pro II monitor anticoagulation and screen for coagulopathy. Neither diagnoses a clot.
Frequently asked questions
No. It supports exclusion in low-probability patients and flags the need for imaging in others. Imaging makes the diagnosis.
Commonly recent surgery or trauma, pregnancy, infection, cancer, liver disease, or older age alone.
No. Assays share no common calibrator, so use the cutoff your own method validates.
Request a Clinical Demo
ISN Medical supplies Roche point-of-care and laboratory diagnostics to Nigerian hospitals and laboratories, including the cobas h 232 and the cobas c111 clinical chemistry analyser, alongside haematology platforms such as the Beckman Coulter DxH 520 (DxH 520 test parameters).
To see a cardiac marker workflow run on your own samples, request a clinical demo on WhatsApp 09139385053, toll free 08002255476, or contact@isnmedical.com , or talk to our diagnostics team.