A Quantitative Glycogen Assay to Verify Use of Self-Administered Vaginal Swabs

Background: Self-administered swabs are used to sample vaginal contents for a variety of clinical purposes including detection of sexually transmitted infections, condom breakage, and vaginal product use. The goal of this study was to determine whether a quantitative glycogen assay can be used to assess whether a swab has been exposed to the vagina to assure study compliance. Study Design: Buccal, skin, or vaginal samples were tested to determine whether a commercial quantitative glycogen assay can differentiate vaginal specimens. In addition, archived remnant de-identified vaginal swabs from clinical trials were tested. Periodic acid-Schiff stain was used to identify glycogen-positive cells as a confirmation test. Results: Glycogen concentrations in eluates of vaginal swabs from reproductive-aged women were significantly higher than those from unused swabs (mean +/- SE, 964 +/- 135 mu g/mL vs. 14.7 +/- 2.5 mu g/mL, P < .001) and swabs exposed to buccal and finger/hand epithelia (40.3 +/- 4.8 and 18.5 +/- 5.4 mu g/mL, P < 0.001). Glycogen concentrations were lower and more variable in vaginal swabs from older perimenopausal/menopausal women (mean +/- SE, 235 +/- 123, P < 0.01). Semen and sample storage longer than 1 year did not affect glycogen detection. Using a cutoff of 100 mu g/mL of glycogen, 30 of 30 vaginal swabs from reproductive-aged women versus 0 of 28 control swabs were positive, for an assay sensitivity of 1 (95% confidence interval, 0.86-1) and specificity of 1 (95% confidence interval, 0.85-1). Periodic acid-Schiff stain correlated with soluble glycogen results but was less specific. Conclusions: The quantitative glycogen assay provides a simple and inexpensive method to validate the use of self-administered swabs for sampling vaginal contents in clinical studies.