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Clinical and Diagnostic Laboratory Immunology, Sep 1995, 634-635, Vol 2, No. 5
Copyright © 1995 by the American Society for Microbiology. All rights reserved.

Blocking antibody assay for confirmation of urogenital Chlamydia infection

I Nachamkin, DL Riddle and J O'Connor
Department of Pathology and Laboratory Medicine, University of Pennsylvania Medical Center, Philadelphia 19104-4283, USA.

We evaluated the Syva MicroTrak Chlamydia Blocking Antibody Assay as a confirmatory assay for the detection of Chlamydia trachomatis in urogenital specimens. During a 5-month period, 109 positives were obtained (4.9%) by the MicroTrak II Enzyme Immunoassay as implemented with the Syva XL automated enzyme immunoassay instrument. Of 98 evaluable samples, 92 (93.9%) were confirmed as positive by the blocking assay, and 3 blocking-negative samples had organisms detected by direct fluorescent-antibody analysis (blocking sensitivity, 96.8%). We found that direct fluorescent-antibody analysis of samples with a specimen-to-cutoff absorbance ratio of < or = 2.0 was a reasonable confirmation alternative and was more cost-effective than the blocking assay.