Accuracy of Vaginal pH Testing Before and After Addition of Sterile Saline

Complaints of vaginal discharge are common, and vaginal pH is important diagnostically. Vaginal pH is measured either directly using pH paper or after wet mount analysis. This study aims to analyze whether a significant change in vaginal pH after saline addition exists.

This prospective, diagnostic accuracy study included 97 persons with a vagina between the ages of 18-80 years who received care at an academic center. Two samples of vaginal discharge were collected, with pH measured by direct application to pH paper and after wet prep analysis. Outcome measurements included pH measurements and demographic variables collected from electronic medical records. A Wilcoxon signed-rank test was performed, with a p value less than .05 considered significant. It was hypothesized that addition of saline to vaginal discharge increases pH artificially.

Primary outcome included pH difference between both samples. Sixty four (66%) of the subjects had a pH difference of 0.50 and 3 (3%) had a difference of 1.0. Twenty nine (30%) of the subjects had no difference. One subject (1%) had a decrease of 0.50 in pH after saline. Reproductive age and nonuse of vaginal medications were significantly associated with a pH difference of 0.50 or higher after saline addition. Of the demographic variables, reproductive age and nonuse of vaginal medications within the past week or the day of collection were associated with a significant pH difference after saline addition (79%, p = .025; 79%, p = .001; 76%, p = .002, respectively).

It may be reasonable to subtract 0.50 from final pH reading in patients of reproductive age and in those who have not used vaginal medications recently.