Amplified nucleic acid techniques (NAATs) are the most sensitive tests for detection of common sexually transmitted infections (STI), C. trachomatis, N. gonorrhoeae, and T. vaginalis, in urine and urogenital specimens. Culture techniques for detection of these pathogens require specialized culture, long turnaround time, and transport conditions that are often not realized in clinical practice.
Special Collection and Transport Instructions
Commercially available NAATs may be validated for use with urine and urogenital specimens (including Pap thin-prep solutions). They are not validated for use with other types of specimens.
NAATs should not be used for the sole testing technique in the evaluation of rape or child abuse.
Specimens must be collected according to the manufacturers instructions, including specimen type and materials. Use collection kits provided by the manufacturer for swab and urine specimen; transfer vials may be provided for thin-prep specimens. Ensure that vials for liquid specimens are filled with the appropriate volume.
Care must be taken to prevent cross-contamination of specimens, for example, at the area used for transfer of urine into a transfer vial.
Transport to the laboratory at refrigerator or room temperature.
Use
Specimens may be submitted for evaluation of sexually active adult patients with symptoms consistent with STDs. Commercially available NAATs for detection of C. trachomatis, N. gonorrhoeae, and T. vaginalis have very high sensitivity and specificity (>95%).
Turnaround time: 24 " �72 hours.
Interpretation
Expected results: Negative.
Positive results: A positive result establishes a diagnosis in patients with compatible symptoms and risk for STD. Positive results must be interpreted with caution in patients with low risk for STD. Repeat testing, ideally performed on a repeat specimen using a different test platform or target sequence, is recommended if a false-positive result is suspected.
Negative results: Infection is unlikely. Poor collection technique, low target levels, or other factors may cause false-negative results.
Limitations
Common pitfalls: Test results must be interpreted in the context of the clinical impression and prior probability of infection. Repeat testing should be performed if false-positive or false-negative test results are suspected.
There is significant overlap in the signs and symptoms of these and other urogenital infections, like bacterial vaginitis, or noninfectious conditions. Laboratory testing for these STIs does not replace physical examination and other testing appropriate for the patients presentation.
Accuracy depends on proper specimen collection: the use of incorrect swabs for specimen collection, improper filling of urine transport tubes, and submission of inappropriate specimen types may result in false-negative results.
Amplified nucleic acid tests should not be used for test of cure evaluations (within 4 weeks of treatment), because DNA may be detectable even after viable organisms have been eliminated.
Other Considerations
As part of routine quality assurance practices, laboratories that perform amplified nucleic acid tests should routinely perform "wipe tests " � of surfaces in the laboratory where NAATs are performed, and perform further evaluation and maintenance according to the test manufacturers instructions. Laboratories should also monitor their reported rates of C. trachomatis, N. gonorrhoeae, and T. vaginalis infections; increasing positivity rates not explained by changes in patient populations tested may be an indication of laboratory contamination; careful evaluation of laboratory procedures should be performed.