Capture-S, a nontreponemal solid-phase erythrocyte adherence assay for serological detection of syphilis.

A solid-phase erythrocyte adherence assay has been developed for the serological detection of reagin antibodies in syphilis. Capture-S (Immucor, Inc., Norcross, Ga.) is a nontreponemal, qualitative screening test for the detection of immunoglobulin G (IgG) and IgM antilipid antibodies in serum or plasma samples from blood donors. The Capture-S assay utilizes a modified Venereal Disease Research Laboratory antigen bound to microtitration wells and anti-IgG- plus anti-IgM-coated indicator erythrocytes as the detection system. The Capture-S assay was evaluated at six separate sites on 10,942 specimens. For patient samples of clinically diagnosed syphilis categories (n = 366), the Capture-S assay yielded a sensitivity of 80.7% versus 80.3% for the rapid plasma reagin (RPR) card test (Becton Dickinson Microbiology Systems, Cockeysville, Md.). In comparative experiments on patient and donor samples (n = 10,222), the Capture-S assay demonstrated a sensitivity of 94% compared to 91.2% for the RPR card test. The Capture-S and RPR card tests produced essentially equivalent specificities of 99.2% and 99.3%, respectively, for this sample population. For five test sites, the Capture-S and RPR card test demonstrated a 98.3% agreement (10,085 of 10,264) of test results. These evaluations indicate that the Capture-S compares favorably to the RPR card test in assay sensitivity and specificity, with the added benefits of ease of use, accommodation of high-volume testing, and potential for automation.