Influence of storing urogenital specimens at -20 degrees C before testing by enzyme amplified immunoassay (IDEIA) to detect Chlamydia trachomatis antigen.

Urogenital specimens from 445 patients, 174 women and 271 men, were tested for antigen to Chlamydia trachomatis by an enzyme amplified immunoassay, IDEIA. The test results for specimens stored at -20 degrees C for means of 9.6 weeks (from each of the first 376 patients) and eight months (from the remaining 69) were compared with results for specimens stored at 4 degrees C and tested within five days. Of 617 specimens (one from the urethra of each patient and one from the cervices of 172 women) cultured for C trachomatis, 90 (15%) gave positive results. The IDEIA results for specimens stored at -20 degrees C were identical with those of specimens analysed without such storage in 96.4% (595/617) of all cases. No difference was seen between urethral specimens from men or women or cervical specimens or between specimens stored for 9.6 weeks compared with those stored for eight months. In 22 cases in which the IDEIA results differed, culture positive results were missed in stored as well as unstored specimens. The median absorbance value above the cut off point for a positive IDEIA result in stored specimens was no lower than in those not stored. The few differences noted probably depended on the sampling technique rather than on the way of storing the specimens.