Makindo Medical Notes.com

D-dimer (or D dimer) is a fibrin degradation product (or FDP), a small protein fragment present in the blood after a blood clot is degraded by fibrinolysis.

About

• Fragment of protein produced during the degradation of fibrin
• Can be a sign of endogenous thrombophilia
• As such it is used to investigate DVT or pulmonary embolus PE

Background

• Fragment of protein produced during the degradation of fibrin
• Can be a sign of endogenous thrombophilia
• In a normal physiological state, there are no circulating D-dimer fragments
• The assay used is highly sensitive and will detect even a very small amount of D-dimer.

Background and uses

• Sensitive but poorly specific investigation. In a normal physiological state, there is no circulating D-dimer fragment
• The assay used is highly sensitive and will detect even a very small amount of D-dimer.
• Even a small quantity may be indicative of a large thromboembolic event and requires investigation (often with a ventilation/perfusion scintigraphy scan or CT pulmonary angiogram).
• In this way D-dimer is very good at excluding DVT and PE but, if the test is positive, it does not in any way guarantee the presence of a clot. D-dimer will typically be highly elevated in DIC.

Age adjusted

• Labs commonly report the test as fibrinogen equivalent units (FEUs) with the cutoff at 500 ng/mL
• Most studies used the FEU values for derivation or validation.
• If reported by the lab as a D-dimer unit (DDU) the cut off is often 230 ng/mL. 2 FEUs equal 1 DDU.
• Age (years) x 10 ug/L for patients > 50 years of age
• Patient age 75 = age adjusted d-dimer of 750 ug/L.
• Using lab cut off of 230 (DDU assay) then formula is Age x 5