D-dimer testing
Indications
D-dimer testing is of clinical use when there is a suspicion of deep venous thrombosis (DVT) or pulmonary embolism (PE) or disseminated intravascular coagulation (DIC). Most situatons require a reisk assessment score (e.g. Wells').
- For patients with a high probability of DVT or PE, a D-dimer may make little difference to the need for further investigations (Doppler, CT pulmonary angiogram etc.) and therefore are not necessary.
- For patients whose clinical presentation is unrelated to DVT, PE or DIC, D-dimers are unlikely to be of value and should not be measured unless there is a clinical indication.
- D-dimers are most useful for patients with a low probability of DVT or PE, where a negative result makes it unlikely that they have DVT or PE.
False positives:
Can be due to:
- liver disease
- high rheumatoid factor
- inflammation
- malignancy
- trauma
- pregnancy
- recent surgery
- advanced age
False negatives
- False negative readings can occur if the sample is taken either too early after thrombus formation
- If testing is delayed for several days.
- Additionally, the presence of anti-coagulation can render the test negative because it prevents thrombus extension.
