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The Sensitivity and Specificity of a Red Blood Cell Agglutination D-Dimer Assay for Venous Thromboembolism When Performed on Venous Blood
Sanjeev D. Chunilal, MB, ChB;
Patrick A. Brill-Edwards, MD;
Pamela B. Stevens, RN;
Jody P. Joval, RN;
Joanne A. McGinnis, RN;
Mala Rupwate, ART;
Jeffrey S. Ginsberg, MD, FRCPC
Arch Intern Med. 2002;162:217-220.
Background Studies evaluating the accuracy of the SimpliRED D-dimer assay for venous
thromboembolism (VTE) have used a capillary fingerstick blood sample, which
requires the test to be performed immediately at the bedside. Initial studies
showed a sensitivity for VTE of 90% to 95% when the assay was performed by
a finite number of experienced health care workers. However, because of the
test's subjectivity, misinterpretation of the result is possible when performed
by inexperienced staff. Recent reports by other investigators indicated a
low sensitivity of this assay for VTE and noted a reduction in sensitivity
(84%) for pulmonary embolism.
Objective To determine the sensitivity and specificity of the D-dimer test performed
in the laboratory by experienced technologists on venous whole-blood samples
in routine collection tubes. If D-dimer testing results accurately detect
VTE when performed in this manner, concerns about the sensitivity of this
assay would be solved.
Methods One hundred forty-eight consecutive patients with suspected VTE underwent
D-dimer testing at the bedside using a fingerstick sample and venous blood
collected into a plain tube. Venous blood was also collected into tubes containing
tri-potassium EDTA, sodium citrate, or a combination of lithium and heparin
for D-dimer testing in the laboratory. In addition, the EDTA tube was refrigerated
overnight at 4°C for retesting at approximately 24 hours. The presence
or absence of VTE was determined by means of objective results of testing
and a 3-month follow-up.
Results Thirty-four subjects (23%) had confirmed VTE (25 with deep vein thrombosis;
9 with pulmonary embolism). All laboratory venous blood D-dimer results showed
sensitivities of 97%, specificities of 61% to 64%, and negative predictive
values of 99%, compared with 88%, 71%, and 95%, respectively, when the results
were obtained by means of fingerstick at the bedside.
Conclusions The SimpliRED D-dimer assay performed in the laboratory on venous blood,
collected into any of 3 routine laboratory tubes, is sensitive and moderately
specific for VTE. Based on this study, immediate bedside testing (particularly
by inexperienced personnel) under suboptimal conditions is unnecessary. Furthermore,
the high sensitivity of refrigerated EDTA samples allows specimens to be stored
or transported (on ice at 4°C) for testing for 24 hours after collection.
From the Department of Medicine, McMaster University (Drs Chunilal,
Brill-Edwards, and Ginsberg and Mss Stevens, Joval, and McGinnis), and the
Department of Laboratory Medicine, McMaster Division of the Hamilton Health
Sciences Corporation (Ms Rupwate), Hamilton, Ontario.
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