Efficacy of D-Dimer and Thrombin-Antithrombin IIIComplex Determinations as Screening Tests before Lung Scanning

thrombin-antithrombin III complex determinations in patients with clinically suspected pulmonary embolism create a discrimination between patients to be further investigated with lung scanning and those who should be investigated for other diseases mimicking pulmonary embolism. The Data-Fi Dimertest Latex Assay, MAbCO Dimertest ELk, and TAT ELk were performed in 100 consecutive patients (26 percent outpatients) who were sent to our institution for lung scanning by their attending physicians because of clinically suspected pulmonary embolism. The D-dimer Latex Assay was positive (>500 ng/ml) in 12 (48.0 percent) of25 patients with high probability ofpulmonary embolism and in one (11.1 percent) of nine with intermediate probability, respectively. Only one patient (1.5 percent) with a normal scan had a positive latex assay, presumably due to inapparent bleeding after a computed tomographic (CT)guided liver biopsy. Referring to 120 ng/ml as upper limit of normal (mean ±2 SD of healthy controls), the D-dimer enzyme immunoassay(EIA)was positive in 21 (84.0 percent) of 25 patients with high probability, in six (66.7 percent) of nine patients with intermediate pmbability and in 40(60.6 percent) of 66 patients with normal/low probability of pulmonary embolism, respectively. The TAT ELk was positive (> mean ±2 SD of healthy controls 3.53 ng/ml) in 18 (72.0 percent) of 25 patients with high probability in five (55.6 percent) of nine patients with intermediate probability and in 16 (24.2 percent) of 66 patients with normal/low probability of pulmonary embolism. A normal result in one of these hemostaseologic tests did not predict a low probability of pulmonary embolism after lung scanning. Thus, it is not justified to exclude patients with clinically suspected pulmonary embolism from further investigation by lung scanning because of a normal result in one of these tests. (Chest 1991; 100:1536-41)