Abnormal vaginal discharge: using office diagnostic testing more effectively

Journal of Family Practice, Oct, 2004 by Linda French, Jennifer Horton, Michelle Matousek

In primary care practice, abnormal vaginal discharge is a common complaint. Signs and symptoms of vaginitis--the most common gynecologic diagnosis in primary care (1)--are not specific for any single underlying cause. (2) Office-based diagnostic testing, which is underused, (3) must be employed to ensure accurate diagnosis and effective treatment. (An article on treatment by the same authors will appear in next month's issue of THE JOURNAL OF FAMILY PRACTICE.)

In a primary-care study, (4) vulvovaginal symptoms including vaginal discharge were due to vulvovaginal candidiasis (VVC) in 27% of patients, bacterial vaginosis (BV) in 21%, trichomoniasis in 8%, Chlamydia trachomah's in 2%, Neisseria gonorrhea (GC) in 1%, and no infection in 34%. Several pathogens may coexist. (2) VVC, BV, and trichomoniasis account for at least 90% of infectious vaginitis. (5) This review will therefore focus heavily on these causes of vaginal discharge among women of reproductive age, including pregnant women.

* CERVICITIS AND PHYSIOLOGIC CERVICAL DISCHARGE

Some women may interpret a physiologic increase in cervical mucous production as abnormal. It occurs cyclically prior to ovulation, is typically transparent and colorless, and may be more pronounced in women with an everted cervix.

Chlamydial infection

In the clinical examination of the cervix, 3 characteristics have been associated with chlamydial infection: yellow endocervical discharge, easily induced cervical bleeding, and opaque cervical discharge. (6) All 3 findings are statistically significant and independently associated with chlamydial infection (odds ratios 2.8, 2.3, and 2.9, respectively). In the primary care study cited above, purulent cervical discharge was found in 6% of women, most commonly testing positive for Chlamydia, less often for GC. (4)

Trichomonas vaginalis may cause cervicitis as well as vaginitis. Mycoplasma genitalium has been proposed as an additional possible pathogen. It was identified in 7% of more than 700 women with mucopurulent cervical discharge seen in a STD clinic with otherwise negative cultures. (7) With cervical discharge that appears to be purulent, testing is warranted as a minimum for Chlamydia and GC (SOR: B). Screening of asymptomatic women less than 26 years of age for Chlamydia is recommended by the US Preventive Services Task Force (SOR: A).

* BACTERIAL VAGINOSIS

Bacterial vaginosis (BV) is neither an inflammatory condition nor an STD, but is a shift in vaginal flora from the normal condition in which lactobacilli predominate, to a polymicrobial flora in which gram-positive anaerobes predominate. In addition to annoying vaginal symptoms, BV is associated with increased risks of more serious conditions such as pelvic inflammatory disease (PID), postoperative infections, and pregnancy-related complications including prematurity. It also increases the likelihood of acquiring HIV in women exposed to the virus. (8,9)

Two principal factors put women at risk for acquiring BV: douching and exposure to a new sexual partner, both of which are thought to disrupt the vaginal ecosystem. (10)

Relative benefits of diagnostic tests

A gold standard test has not been established for BV. In about 50% of asymptomatic women, culture results are positive for flora such as Gardnerella vaginalis. (5) While Amsel's criteria are often used as a reference and generally suffice for the evaluation of symptomatic women, the best candidate for a gold standard test is probably Gram stain assessment using Nugent's criteria (described in this section). (11) Lack of leukocytes in the vaginal fluid supports a diagnosis of BV. A finding of white blood cells in excess of the number of vaginal epithelial cells suggests an inflammatory process (SOR: C). (12)

Amsel's criteria with wet mount. The diagnostic approach most commonly used in the office is Amsel's criteria--homogenous discharge, positive whiff-amine test, pH >4.5, and clue cells found on wet-mount microscopy (see How to perform a wet mount). (13) Three of 4 criteria deemed positive is considered diagnostic. If Gram stain is used as the reference standard, then Amsel's criteria have 70% sensitivity and 94% specificity for diagnosing BV. (14) An analysis of the individual criteria follows. The positive and negative predictive values of each compared with the whole group as reference standard is displayed in Table 1.

Homogenous discharge. A thin, homogenous, grayish discharge is traditionally associated with BV. However, it is not specific to BV, being found commonly also in women with culture results positive for VVC or no diagnosis of vaginitis. (2,15) It is the criterion least likely to be consistent with the whole group, seen in about half of women BV-positive and over one third of women BV-negative using Amsel's criteria as the reference standard. (15)

Whiff test. The whiff test is performed by adding drops of 10% potassium hydroxide solution to the vaginal fluid. A positive result is a "fishy" amine odor. In a study (16) of 100 women complaining of malodorous discharge, a positive whiff test was predictive of positive culture results for anaerobic flora such as Bacteroides sp. with sensitivity 67%, specificity 94%, and a positive predictive value of 95%. The whiff test was not positive in any of the 5 cases with positive culture results for G vaginalis in the absence of anaerobes. There were also 12 cases positive for anaerobes without G vaginalis.