Laboratory Tests and Ancillaries

Settings Where Diagnostic Lab Tests are Not Available

Consider syndromic management for patients presenting with vaginal discharge. A spontaneous complaint of abnormal vaginal discharge is most commonly a result of a vaginal infection. T vaginalis, C albicans and bacterial vaginosis are the most common causes of altered vaginal discharge. In settings where Gram stain can be carried out in an efficient manner, identification of T vaginalis can be attempted. In settings where diagnostic tests for the etiologic agent of vaginal infection cannot be done, it is recommended that patients be offered treatment for bacterial vaginosis and T vaginalis. A Pap smear is not a reliable test for diagnosing vaginitis, and confirmatory diagnostic tests are recommended when incidental findings of trichomoniasis, bacterial vaginosis, or vulvovaginal candidiasis are noted on a Pap smear.

Specimen Collection in Settings Where Diagnostic Lab Tests are Available



Vaginitis Trichomoniasis, Candidiasis, Bacterial Vaginosis_DiagnosticsVaginitis Trichomoniasis, Candidiasis, Bacterial Vaginosis_Diagnostics




Collect vaginal specimens for the following:

  • pH test: Specimen should be obtained from the mid-portion of the vaginal side wall to avoid false elevations in pH secondary to cervical mucus, semen, blood, lubricants or other substances.
  • Amine odor or whiff test: Considered positive if release of fishy odor occurs when swab from vaginal discharge is placed in 10% KOH
  • Wet mount microscopy with saline or 10% KOH
  • Gram stain: Dry Gram stain is the definitive diagnostic test for bacterial vaginosis
  • High vaginal swabs help in diagnosing T vaginalis, bacterial vaginosis, vulvovaginal candidiasis, or other genital tract infections, particularly in pregnant, postpartum, or post-instrumentation patients with recurrent or inconsistent signs and symptoms or in treatment failure
  • Culture is used to identify Candida when microscopy is inconclusive or in recurrent infections where identification of specific causative agent is useful
  • Polymerase chain reaction (PCR)/multiplex is considered the best diagnostic tool for specific species identification but may not be available in all settings


Lab Tests for Trichomoniasis

For trichomoniasis, the pH is >4.5. The amine odor or whiff test is not consistently positive. Wet mount microscopy with saline with a specimen from the posterior vaginal fornix may reveal motile flagellated trichomonads with abundant polymorphonuclear cells (PMNs). This has low sensitivity (as low as 40-60%) and should be performed as soon as possible after taking the sample, as motility is decreased with time. In the absence of colpitis, the pseudocyst form of T vaginalis (immobile and smaller than the active form) may be present. Gram stain may reveal T vaginalis and/or PMNs. The culture has higher sensitivity (88%) than microscopy. Culture is considered in patients with negative wet mount test results, history of trichomoniasis with persistent symptoms even after treatment, or positive T vaginalis on Pap test.

The nucleic acid amplification test (NAAT) has the highest sensitivity (88-97%) for T vaginalis detection. This should be the test of choice where diagnostic lab tests are available. Rapid tests for trichomoniasis include immunochromatographic capillary flow dipstick technology-based tests (eg OSOM Trichomonas rapid test), nucleic acid probe tests (eg Solana trichomonas assay, AmpliVue trichomonas assay), and antigen-detection testing; however, availability may be limited.  Cervical screening (Pap smear) alone is not diagnostic of trichomoniasis.

Lab Tests for Bacterial Vaginosis

The tests should fulfill three out of four of the Amsel’s criteria: 

  • Abnormal thin, homogenous, gray, or white vaginal discharge
  • pH of >4.5
  • Amine odor or whiff test is positive
  • A wet mount with saline shows the presence of >20% clue cells (epithelial cells with granular appearance and obscured borders caused by adherent bacteria)


A Gram stain may reveal a shift in vaginal flora with a decrease in large Gram-positive rods (Lactobacilli) and a marked increase in smaller Gram-variable coccobacilli (Gardnerella) and curved Gram-negative rods (Mobiluncus) (Nugent’s criteria, and Hay-Ison criteria). This is the gold standard in diagnosing patients who fail to fulfill Amsel’s criteria. New lab tests that detect Gardnerella vaginalis DNA, vaginal fluid sialidase activity (eg OSOM BV Blue test) or other commercial microbiome-based nucleic acid amplification assays (eg BD MAXTM vaginal panel) have similar specificity and sensitivity compared with office-based testing. Culture is not recommended because of its low specificity. Pap smear is also not diagnostic of bacterial vaginosis due to its polymicrobial nature

Lab Tests for Vulvovaginal Candidiasis

For vulvovaginal candidiasis, the pH is 3.5-4.5. Vaginal pH is usually normal as the normal numbers of lactobacilli are generally maintained. The amine odor or whiff test is negative. A wet mount with 10% KOH typically shows budding yeast, spores, and/or branching pseudohyphae. A Gram stain may reveal PMNs, budding yeast, and/or branching pseudohyphae. Culture is positive for yeast species. Lab tests are not routinely indicated and should be obtained in patients with recurrent or resistant vulvovaginal candidiasis, possible non-albicans candidiasis, or symptomatic patients with negative microscopy. DNA probe testing with PCR is also available for complicated vulvovaginal candidiasis.