Hi George, At our hospital lab we currently run manual FDPs (Thrombo-Wellcotest) andquantitative D-dimers on the Diagnostica Stago Evolution. We have been trying to come up with justification for eliminating the FDP testing, but our main road block seems to be that quantitative D-dimers are always elevated in pregnancy, especially 3rd trimester, and there are no normal ranges available for pregnant women.
Our OB physicians are not comfortable changing over to D-dimer testing for their high risk OB patients with disseminated intravascular coagulation (DIC) or potential DIC. Do you have any information I could give these physicians on how to interpret D-dimer results in pregnant patients, and/or how to convince them that D-dimer is the preferred test over FDP?
Hello, and thank you for your question. For help I turned to my colleague, Dave McGlasson, who provided me with several articles about D-dimer concentrations in pregnancy. The best is Kline JA, Williams GW, Hernandez-Nino J. D-dimer concentrations in normal pregnancy: new diagnostic thresholds are needed. Clin Chem 2005;51: 825-9. This article clearly illustrates the rise of D-dimer concentrations during pregnancy to approximately 500 to 1800 mcg/L (95% confidence interval), but does not provide sufficient power to establish reference intervals.
However, there is a useful reference, Lehman CM, Wilson LW, Rodgers GM. Analytic validation and clinical evaluation of the STA LIATEST immunoturbidimetric D-Dimer assay for the diagnosis of disseminated intravascular coagulation. Am J Clin Pathol 2004;122: 1978-84 (attached below). Lehman uses receiver operatic characteristic (ROC) analysis to establish a D-dimer decision point, 8.2 mcg/mL (8200 mcg/L, area under the ROC curve 0.94) and compares it to prothrombin time (PT), partial thromboplastin time (PTT), and a semiquantitative manual D-dimer method.
Of course, your physicians know the DIC diagnosis is based on more than FDPs or the D-dimer, and should include thrombocytopenia, hypofibrinogenemia, prolonged PT and PTT, peripheral blood film schistocytes, and clinical evidence of microvascular hemorrhage or thrombosis. Nevertheless, the Lehman article illustrates just how sensitive the quantitative D-dimer is for DIC compared to the semiquantitative test, owing to its striking increase in acute disease.