This is based upon the determination of d-dimer levels and upon the negative predictive value (NPV) of the test. A d-dimer value of less than 0.5 µg/mL, determined using a method validated in this indication may be used to rule out the existence of DVT or of PE within the previous week.
The power of the test may be improved if it is carried out after assessment of clinical risk using a validated score suitable for the clinical setting (DVT or PE), such as the Wells score. Use of such scores limits recourse to d-dimer assay to situations involving low or moderate clinical risk.
Medical imaging is routinely carried out as a first-line investigation where there is a high clinical risk. For low or moderate clinical risk, a D-dimer value below the exclusion threshold is sufficient to rule out a diagnosis of DVT or PE within the preceding week. However, due to the lack of specificity of high D-dimer levels and to the low positive predictive value (PPV) of the test, imaging must be carried out where the D-dimer level exceeds the exclusion threshold.