Confirmatory assay increases specificity of the chlamydiazyme test for Chlamydia trachomatis infection of the cervix

Abstract

Enzyme immunoassays for the detection of chlamydial antigens are commonly used to diagnose Chlamydia trachomatis infection. As is true for ail nonculture methods, the specificities of these tests are a concern. A confirmatory blocking assay (Abbott Laboratories, North Chicago, Ill.) was evaluated at four sexually transmitted disease test sites. This assay is designed to confirm true-positive Chlamydiazyme (CZ) specimens and to identify false-positive CZ reactions caused by cross-reacting bacteria. Cervical specimens were collected from 2,891 women. Chlamydia prevalence by tissue culture (TC) was 9.2% (266 of 2,891 specimens). Compared with TC, the sensitivity and specificity of CZ were 78.9% (210 of 266 specimens) and 98.2% (2,577 of 2,625 specimens), respectively. There were 48 CZ false-positive reactions. The direct fluorescent-antibody test (DFA) was positive for 31 of 48 false-positive reactions, indicating culture misses. Thus, when the standard was both TC and DFA, CZ sensitivity was 81.1% and CZ specificity was 99.3%. Of the 17 CZ-positive patients who were negative by both TC and DFA, 3 were negative on repeat CZ and Il of 14 were identified as false positive by the confirmatory assay. The confirmatory test was positive for CZ-positive women who were positive by TC or DFA. Use of the confirmatory test, which increased the specificity to 99.9%, would increase confidence in positive CZ results and make the test more useful for screening populations with a low prevalence of C. trachomatis infection.

Nachweis von Chlamydia psittaci in Vaginalausfluß von Rindern: Eine notwendige Erweiterung der bakteriologischen Diagnostik zur ätiologischen Klärung von Fruchtbarkeitsstörungen beim weiblichen Rind

“…Voraussetzung fur die Verknupfung der beiden Bedingungen war, den 'cut-off' des ELISA anhand der OD der prainkubierten Proben nach der oben aufgefuhrten Formel zu berechnen (TIJSSEN, 1985). (HIPP et al, 1987;KELLOGG et al, 1990;MARDH et al, 1990;MONCADA et al, 1990;MILLS et al, 1992;OLSEN und SAMBOL, 1993;WARREN et al, 1993) (MILLS et al, 1992).…”

Current Methods of Laboratory Diagnosis of Chlamydia Trachomatis Infections

“…Proficiency in specimen collection and transport is paramount to accuracy in diagnostic testing for C. trachomatis. Both the sensitivity and the specificity of diagnostic tests for C. trachomatis have been shown to be directly related to the adequacy of the specimen (82,95,137,159,187). The lack of specimen adequacy remains a serious shortcoming in many screening programs and research studies.…”

“…The third method is the least desirable since it depends on the same target as the initial test for confirmation. However, since test manufacturers are now making this type of confirmation method commercially available, it is widely used and is reported to be effective in increasing the specificity of tests (94,114,136,137,203).…”

Alternate Nucleic Acid Targets Can Be Used To Create a Composite Standard To Evaluate Clinical Performance of Nucleic Acid Amplification Tests

“…When these immunoassays were compared to isolation by cell culture, it became obvious that the isolation procedure was a flawed reference standard, while highly specific cell culture was well less than 100% sensitive. Using different immunoassays with different antigenic targets, it became clear that at least some of the antigen-positive/culture-negative results actually were true positives (8).…”