Ease of New DNA Assays May Lead to Overuse.

ATLANTA -- DNA amplification methods of testing patients for Chlamydia trachomatis are far easier than traditional tissue culture methods, but their simplicity may be luring physicians to use them inappropriately, Dr. Michael Rein warned at the annual meeting of the American College of Physicians--American Society of Internal Medicine. Interest in DNA amplification methods that use urine or self-collected vaginal specimens to test for C. trachomatis is picking up steam, because they're cost effective and allow for the elimination of invasive genital and pelvic examinations, said Dr. Rein, an infectious disease expert from the University of Virginia, Charlottesville.

At the same time, both ligase chain reaction (LCR) and polymerase chain reaction (PCR) methods are at least as sensitive as traditional tissue culturing methods, which have a sensitivity of 85% and a specificity of 100%.

When urine is used, DNA amplification methods have a sensitivity of around 90%. The sensitivity of self-collected vaginal samples analyzed by LCR is slightly better (93%) than with PCR analysis (88%). A review of the literature has shown that both methods have specificities of 99%, regardless of the specimen used, Dr. Rein said.

Cost is also a key advantage. C. trachomatis is an intracellular pathogen and so it has been traditionally diagnosed by tissue culture, which is expensive. Compared with PCR and LCR analyses, which cost $5.41 and $5.32, respectively, materials for the traditional culture test cost $22.56, he said.

The newer DNA amplification methods are also far more sensitive in terms of the number of organisms required for a positive test compared with the first culture-independent test, the enzyme-linked immunosorbent assay (ELISA). The ELISA method of analyzing cervical samples has a sensitivity of only about 70% and a specificity of 95%.

With all ...