Disseminated Intravascular Coagulation (DIC) Panel |
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The FDP assay has been available as a screening test for the diagnosis of disseminated intravascular coagulation (DIC) for many years, reflecting activation of fibrinolysis. In the mid-1980's the D-dimer assay became available for detection of a specific cross-linked fibrin degradation product, reflecting not only activation of fibrinolysis but also thrombin generation, both important dimensions of DIC. The widely used semi-quantitative latex agglutination assay for D-dimer was more specific but less sensitive than the FDP assay for diagnosis of DIC. For this reason, it was recommended that both FDP and D-dimer assays should be used, to maximize sensitivity and specificity.
Several highly sensitive quantitative automated D-dimer assays have become available, primarily for use in exclusion of deep vein thrombosis and pulmonary embolism. This new assay would be expected to be more sensitive than the FDP assay for diagnosis of DIC. To investigate this, we collected the results of 50 consecutive samples where both FDP and D-dimer assays were ordered and either one or both tests were positive. As shown in the table, D-dimer was positive in 50/50 samples (sensitivity 100%), whereas FDP was positive in 38/50 samples (sensitivity 76%). In no sample was FDP positive and D-dimer negative. This superior sensitivity of the new D-dimer assay in addition to its superior specificity for DIC diagnosis supports its use as a replacement for the FDP assay.
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D-Dimer Positive |
D-Dimer Negative |
FDP Positive |
38 |
0 |
FDP Negative |
12 |
- |
The FDP assay detects fibrinolytic breakdown products of fibrinogen and cross-linked fibrin, and is positive in both primary fibrinolysis (primary activation of the fibrinolytic pathway) and secondary fibrinolysis (usually associated with DIC). The D-dimer assay is specific for cross-linked fibrin degradation products, and is positive only in secondary fibrinolysis. It may therefore be argued that an FDP assay should be available for diagnosis of primary fibrinolysis. Primary fibrinolysis appears to be exceedingly rare, however, as evidenced by the rarity in our experience of samples showing positive FDP and negative D-dimer assays. Furthermore other laboratory tests can be used to diagnose primary fibrinolysis, such as low fibrinogen and alpha-2-antiplasmin values in the presence of a normal platelet count and antithrombin level (the latter two values are decreased in DIC with secondary fibrinolysis).
The panel of tests for diagnosis of DIC should include PT, APTT, fibrinogen, platelet count and D-dimer assay.
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