From the Guidelines
False negative results for Trichomonas vaginalis testing can occur and should be considered when symptoms persist despite negative test results, with the most recent and highest quality study suggesting that nucleic acid amplification tests (NAATs) have much higher sensitivity (95-99%) compared to wet mount microscopy (50-70%) 1. The sensitivity of testing methods varies significantly, and false negatives may occur due to low organism load, improper specimen collection, delayed processing, recent antibiotic use, or menstruation.
- Factors that increase false negative risk include:
- Testing during menstruation
- Recent douching
- Inadequate sample collection If clinical suspicion remains high despite a negative test, consider repeating the test using a more sensitive method like PCR or treating empirically with metronidazole 500 mg orally twice daily for 7 days or a single 2-gram dose 1. Alternative treatments include tinidazole 2 grams as a single dose. For more accurate results, collect specimens before menstruation, avoid douching for 24 hours before testing, ensure proper specimen handling, and consider using multiple testing methods when clinical suspicion is high 1. It is essential to note that the diagnosis of vaginal trichomoniasis is usually performed by microscopy of vaginal secretions, but this method has a sensitivity of only about 60%--70%, and culture is the most sensitive commercially available method of diagnosis 1. However, NAATs like PCR have become the preferred method for diagnosis due to their high sensitivity and specificity 1.
From the Research
False Negative Results for Trichomonas vaginalis (TV) Infection
- The possibility of a false negative result for Trichomonas vaginalis (TV) infection is a concern in diagnostic testing 2, 3, 4, 5, 6.
- A study found that testing too soon post-treatment may detect remnant nucleic acid that is not from viable organisms, falsely misclassifying a person as infected 2.
- The sensitivity of different diagnostic methods for TV infection varies, with wet mount microscopy having a sensitivity of 38% to 60% 3, 5, 6, culture having a sensitivity of 73.33% to 88% 3, 5, 6, and nucleic acid amplification tests (NAAT) having a sensitivity of 88% to 92% 3, 4, 5, 6.
- The use of a combination of diagnostic methods, such as wet mount microscopy and culture, or NAAT, can improve the detection of TV infection and reduce the likelihood of false negative results 3, 5, 6.
- A stepwise approach using an additional rapid test for wet-mount-negative women is recommended for adolescent women regardless of clinical factors 5.
- The optimal timing for TV retesting after completion of treatment is 3 weeks for those receiving multidose metronidazole and 4 weeks for those receiving single-dose, though sexual reexposure and false negatives should be considered 2.