Detection of Chlamydia trachomatis by direct fluorescent antibody staining. Results of the College of American Pathologists Proficiency Testing Program, 1986-1992.

Since 1986 the College of American Pathologists has provided a proficiency testing program for laboratories that use the direct fluorescent antibody test for direct detection of Chlamydia trachomatis in clinical specimens. The number of survey participants increased from about 200 in 1986 to about 800 in 1992, and in all years the majority used reagents produced by Syva Co (Palo Alto, Calif), although the percentage decreased from 82% in 1986 to 68% in 1992. Performance on positive specimens varied based on specimen fixation method, number of elementary bodies present, serotype, and specific product used, and declined when the specimen was fixed with acetone prior to shipping or contained fewer than 50 elementary bodies, particularly when the elementary bodies were of serotype L2. Performance with negative specimens was also variable, with 79% to 96% of all participants, and over 90% since 1991, responding correctly. In the last 1992 survey, an ungraded specimen (a five-well slide containing latex beads incorporated with fluorescein isothiocyanate) and a questionnaire were included to assess the potential influence of laboratory operations on performance. Responses to the questionnaire and the ungraded specimen suggested that the level of experience of testing personnel affected performance. A test for trend in error rate across the number of years that a laboratory had offered the Chlamydia direct fluorescent antibody test indicated that error rate declined as degree of experience with the test increased.