Impact of the Sampling Site in the Result of Wet Mount Microscopy

Wet mount microscopy (WMM) is an ancillary test in the diagnosis of vulvovaginitis. However, there are little data about the impact of the sampling site. Our main objective was to determine the agreement between samples collected from different vaginal sites.

Five vaginal samples (one from each of the fornices and one from the lower third) were collected from 50 consecutive women and evaluated using phase-contrast WMM, including the following: lactobacillary grade, presence of other bacteria, clue cells, inflammation, and atrophy. Global percentage of agreement, κ index [poor (<0), slight (0.01-0.20), fair (0.21-0.40), moderate (0.41-0.60), substantial (0.61-0.80), and almost perfect (0.81-1)], sensitivity and negative predictive value were calculated.

Global percentage of agreement was high for all individual parameters (>75%), but low for the final diagnosis (57%). Agreement rate was substantial or almost perfect for the evaluation of normal versus abnormal flora, substantial for the presence of absence of bacteria other than lactobacilli and for the presence of clue cells, and moderate to almost perfect for the presence of dysbiosis and cytolysis. Agreement rates were worse for inflammation, atrophy, and the presence of Candida. The lower third of the vagina had the highest sensitivity for Candida (0.6, 95% CI = 0.41-0.86) and bacterial vaginosis (0.92, 95% CI = 0.73-1.00), whereas the anterior fornix performed better for cytolytic vaginosis (0.75, 95% CI = 0.43-0.93).

There is some variation in the results according to the sampling site, which may be overcome by collecting 2 samples (anterior fornix and lower third of the vagina).