Various studies have found that vaginal pH in the absence of vaginal infection is 4.5 or less during the reproductive years. This pH level is maintained because of the action of estrogen on the vaginal mucosa, which supports the growth of normal vaginal bacteria that produce metabolic byproducts. The latter cause the vaginal mucosa to stay acidic. In the absence of vaginitis, elevated pH values may indicate low circulating estrogen levels or a poor response to estrogen replacement therapy.

In the past, measuring for vaginal pH consisted of pressing pH paper against the vaginal wall using the fingers or forceps or placing the paper in vaginal pool secretions from the vaginal fornix. Contamination with cervical mucus, blood, or semen, however, could result in elevated pH values. To obtain a more accurate reading of the vaginal pH level, a vaginal pH device was developed that holds Nitrazine Paper against the vaginal wall for five seconds and determines the pH value by comparing the color change in the paper with a colorimetric chart. Roy and associates compared vaginal pH with follicle-stimulating hormone (FSH) levels in establishing the menopause status of women.

They reviewed 16 studies that assessed vaginal pH before and after estrogen administration, two epidemiologic studies that evaluated FSH or vaginal pH and menopause, and a study from one practice that had recorded the vaginal pH of women who had not menstruated for more than 12 months. Vaginal pH, FSH, and serum estradiol levels, the absence or presence of hormone therapy, and body mass index were evaluated to calculate the sensitivity, specificity, and positive and negative predictive values.

The weighted average of vaginal pH was 6.0 in menopausal women not receiving estrogen therapy and 4.5 after estrogen therapy was initiated. FSH values of 15 mIU per mL or greater had a sensitivity of 65 percent, while FSH values of 20 mIU per mL or greater had a sensitivity of 68 percent. One study found that a pH value of more than 5 had a sensitivity of 64 to 67 percent. A vaginal pH greater than 4.5 in women with no estrogen therapy had a positive predictive value of 89 percent and a sensitivity of 74 percent. The 95 percent confidence interval sensitivities and positive predictive values of vaginal pH and FSH to diagnose menopause overlapped.

The authors conclude that a vaginal pH greater than 4.5 indicates menopause in women who are without vaginitis and are not receiving estrogen therapy. They add that vaginal pH is similar to FSH levels in establishing the diagnosis of low estrogen levels or menopause, and that a vaginal pH of 4.5 or less can be used to monitor adequate response to estrogen replacement therapy.