Variability of vaginal pH determination by patients and clinicians

Measurement of intravaginal pH provides a reasonable assessment of vaginal health but is fraught with the potential for several sampling errors. The purposes of the study were to determine the variability of self-sampled vaginal pH among women using an inexpensive swab-based pH test compared with a clinician-obtained specimen, and variability of vaginal pH within 3 regions of the normal vagina.

In this cross-sectional study, women obtained a vaginal specimen using a cotton-tip applicator, transferred it to pH paper, and interpreted the results. A clinician also blindly interpreted these tests. Thereafter, a clinician obtained 3 swab specimens from the proximal, middle, and distal vagina for pH testing. Results were compared using Wilcoxon signed rank test, interclass correlation coefficients, Bland-Altman plots, and mixed-model analysis of variance.

Interclass correlation coefficients were moderately high comparing subjects with clinician for the swab-based pH test (0.74). Subjects' swab pH values (4.5) were significantly lower than clinicians' pH values (4.7, P = .0001). Intravaginal pH did not vary between the 3 anatomic locations.

Self-sampled intravaginal pH interpretations vary slightly compared with clinician-obtained specimens. Because swab pH sampling does not detect an intravaginal pH gradient in normal women, self-sampling technique may vary considerably without affecting outcomes. Our findings support self-sampling for vaginal pH before using over-the-counter products for presumed vaginitis.