Evaluation of a microdot immunofluorescent antigen detection test for Chlamydia trachomatis.

OBJECTIVE--To evaluate a centrifuge enhanced direct immunofluorescent antigen test (MD test), compared with conventional culture and ELISA testing in the diagnosis of Chlamydia trachomatis infection. SETTING--A District General Hospital situated 30 miles from a University Department of Medical Microbiology. SUBJECT AND METHOD--A prospective study on specimens from 638 patients. Culture was performed on 348 specimens from genitourinary medicine patients and ELISA testing was carried out on 272 specimens from Gynaecology patients. RESULTS--When compared with culture the MD test had a sensitivity of 90.6%, specificity of 96.8%, positive predictive value of 74.3% and a negative predictive value of 99%. When compared with confirmed ELISA results the MD test had a sensitivity of 100%, specificity of 98.8%, positive predictive value of 78.5% and negative predictive value of 100%. CONCLUSION--The MD test compares favourably with other chlamydial diagnostic techniques and in our setting is preferable to sending specimens for chlamydial culture. It is not suitable as the sole diagnostic method for screening large numbers of specimens but is a cost effective confirmatory test for positive ELISA results.