Vaginal pH

Vaginal pH (Lat. pondus Hydrogenii — the weight of hydrogen) is a biochemical indicator reflecting the concentration of hydrogen ions in the vaginal transudate.

The physiological norm for women of reproductive age is strictly maintained in the range of 3.8–4.5 (acidic reaction).

Etiology and pathophysiology

The acidic environment of the vagina is maintained by lactic acid, which is the end product of anaerobic glycolysis of glycogen in vaginal epithelium. This metabolic process is carried out by lactobacilli (Lactobacillus spp.).

Low pH is a major factor of non-specific humoral immunity (“acidic barrier”): it inhibits the adhesion and proliferation of most acid-averse pathogenic and opportunistic microorganisms (gardnerella, streptococci, gonococci), but is optimal for the endogenous flora.

Clinical significance

Determination of pH with indicator strips is a basic screening test for the differential diagnosis of vulvovaginal infections:

• pH ≤ 4.5 (normal): if there are complaints, it is typical for candidal vulvovaginitis (Candida species are acid tolerant) or cytolytic vaginosis.
• pH > 4.5 (alkaline environment): indicates a decrease in the level of lactobacilli and is characteristic of bacterial vaginosis, trichomoniasis, aerobic vaginitis. In menopause, an increased pH is a marker of atrophic vaginitis (due to a substrate deficiency — glycogen).