Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (269 page)

   Diagnosis of BV is based on ≥3 of the following (Amsel criteria):

   Homogeneous, thin, whitish adherent vaginal secretions

   Positive “whiff” test

   Presence of clue cells on wet mount (>20% of vaginal squamous cells coated with small coccobacilli) in 90% of cases

   Vaginal pH >4.5

   Gram stain, using standardized interpretive criteria, is considered the gold standard for the diagnosis of BV. BV is characterized by a loss of gram-positive rods, with overgrowth of small, curved gram-negative bacilli and gram-variable coccobacilli. Gram stain of vaginal secretions has been demonstrated to have high positive and negative predictive values (90% and 94%, respectively) compared to diagnosis using the Amsel criteria. Interpretation is based on the number of clue cells (≥2 clue cells per 20 fields) and the proportion of bacterial morphotypes (non-
Lactobacillus
>
Lactobacillus
). See Table
8-1
.

Trichomoniasis

   This sexually transmitted protozoal infection is caused by
Trichomonas vaginalis
; it is the most common nonviral STI.

   Women typically present with acute, inflammatory vaginitis. Most patients (approximately 70%) present with vaginal and urethral inflammation resulting in burning, itching, dysuria, and other symptoms associated with increased vaginal secretions. Secretions are described as greenish, frothy, and foul smelling in a minority of patients.

   Direct detection: Rapid diagnosis may be possible by microscopic examination. Vaginal secretions typically show increased pH (>4.5) and increased numbers of PMNs. Motile trichomonads, with typical twitching or “falling leaf” motility, are diagnostic but seen in only 50–70% of cases. Organisms may lose motility as early as 10 minutes after collection.

   Specific diagnosis requires laboratory testing (see Table
8-1
).

   Molecular tests:

   FDA-approved NAATs (e.g.,
Trichomonas vaginalis
assay) have become the gold standard for diagnosis, providing the highest sensitivity and specificity with decreased turnaround time compared to culture.