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Qualitative and Quantitative D-dimer

On Thursday, February 21, 2008, Colleen Marinucci from Elmendorf AFB wrote:

We perform the SimpliRED® qualitative d-dimer assay (AGEN Biomedical Ltd,  Brisbane, Queensland, Australia, distributed in the USA by American Diagnostica, Inc, Stamford, CT). Our internal med docs wondered why a patient with a small pulmonary embolism tested negative. This patient has, among other problems; pancreatitis, pulmonary hypertension, COPD and lupus anticoagulant. We have investigated the quantitative D-dimer on the Stratus and ACL 9000 but do not have access to ELISA. Any suggestions for improving our d-dimer dilemma? Thanks

The SimpliRED® D-dimer assay is a qualitative autologous whole blood agglutination assay that detects >0.20 mg/L cross-linked fibrin degradation products (FDPs) including D-dimer.

From the SimpliRED package insert, the clinical diagnosis of pulmonary embolism (PE), confirmed by radionuclide lung scans or contrast enhanced helical chest computed tomography plus selective use of pulmonary angiography and venous ultrasonography in a six-month follow up yielded the following clinical data:

Sensitivity: 93.8 % (95% CI = 84.8 – 98.3)
Specificity: 67.1% (95% CI = 61.9 – 72.3)
Further, the sensitivity for diagnosis of PE improved to 98.4% (95%Cl 91.6 – 100.0) when an abnormal alveolar dead space added to the clinical diagnostic algorithm. The posterior probability of PE with normal results on both tests was 0.75%.

Most SimpliRED sensitivity data are similar to those of the quantitative ELISA and latex immunoassay methods available, however in a 2000 publication, Farrell S, Hayes T, Shaw MA. Negative SimpliRED D-dimer assay result does not exclude the diagnosis of deep vein thrombosis or pulmonary embolus in emergency department patients. Ann Emerg Med 2000;35:121-5, for patients with suspected PE, the sensitivity and negative predictive value were 68% and 83%, respectively, indicating a relatively high false normal rate.

Colleen, it may be in the case you quoted, the PE had occurred a few days or weeks before, as implied by the diagnosis of pulmonary hypertension. D-dimer levels tend to normalize over a few weeks following an event. Further, you may wish to check the patient’s hematocrit, as the SimpliRED results have not been validated for hematocrits below 40 or above 50%.

If you wish to validate a quantitative latex immunoassay method, all those that are offered are reliable, have good negative predictive values, and are easier and more rapid than ELISA methods. Geo.

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