What diagnostic tests can you do?

Diagnostic tests play a pivotal role in identifying the underlying causes of symptoms and determining the appropriate course of treatment. Despite their importance, these tests are sometimes neglected or overlooked due to the discomfort they may cause patients, such as when taking swabs. Nevertheless, these diagnostic procedures are vital for accurately pinpointing the source of a medical condition, thereby preventing misdiagnosis and the unnecessary or incorrect use of antimicrobials. Ultimately, accurate diagnostics lead to the correct treatment, benefiting both patients and physicians through a prompt and effective resolution of symptoms.

  • Vaginal pH

    Low pH (< 3.8) Normal pH (3.8-4.5) High pH (>4.5)

    Candida can thrive in low pH

    Overgrowth of Lactobacillus species (Vaginal cytolysis)

    VVC (or thrush) can present with normal vaginal pH ~4

    BV (pH usually around 5-6)

    Trichomoniasis (pH value could be even > 6.5)

  • Whiff test (odour test)

    • Vaginal discharge sample is mixed with a drop of 10% KOH (potassium hydroxide) solution and then “sniffed”. A fishy odour indicates a BV infection.

  • Microscopic analysis

    • Using a light microscope, a drop of the vaginal discharge is added to 2 microscope slides. To one, a drop of saline is added and to the other a single drop of a 10% KOH solution. This solution dissolves bacterial cell membranes as well as epithelial cells, but not the cellulose found in the cell walls of fungi, which can then be visualized and analysed. On the saline slide, Lactobacillus organisms can be seen in the form of distinct rod shapes size 1-15 µm.
    • The presence of vaginal epithelial cells which are heavily covered with bacteria cells is an indication of BV (“clue” cells).
    • Candida presence will show typical pseudohyphae and budding yeast cells structures and spores.
    a) Microscopic image of gram-positive rod-shaped lactobacilli (from Padmavathi et al., 2018, doi: 10.1016/j.tim.2004.05.008). b) Microscopic image of yeast pseudohyphae (from Sudbery et al., 2004, doi: 10.1016/j.tim.2004.05.008).
  • Amsel criteria (for BV diagnosis)

    • Three out of four signs need to be positive:
      • abnormal discharge (thin homogenously milky, grey or yellow)
      • presence of at least 20% of “clue” cells on saline (0.9%) wet mount
      • vaginal pH >4.5
      • unpleasant odour with KOH whiff test
  • Nugent score (for BV diagnosis)

    • Nugent score is considered a gold standard test
    • It requires technical experience
    • It is a scoring system
    • Calculates the relative number of bacterial morphologies under gram-stained vaginal discharge smears
    • Normal vaginal flora will have score of 0-3, intermediate flora score 4-6, and BV flora score 7-10
    A. Normal Vaginal flora (0-3), B. Altered Vaginal flora (4- 6), C. BV flora (7-10).   Examples of Nugent score and vaginal gram-stained vaginal smears microscopic images (taken from Wang et al., 2021, doi: 10.1128/JCM.02236-20).
  • PCR analysis

    • Vaginal swab can be tested for presence and quantity of DNA of specific organisms (BV causing bacteria, Candida species, aerobic bacteria, Lactobacillus species, pathogen viruses, STI causing pathogens).
    • There are test-kits that could be used in clinics or sent to patients for taking a vaginal swab at their homes (NutriPath, Juno, Evvy, i-screen, invivo, etc.)
    • The most common bacteria causing vaginal infections or inflammation are given in the table below.
    BV VVC Trichomoniasis Aerobic vaginitis
    Gardnerella vaginalis
    Atopobium vaginae
    Candida albicans
    Candida krusei
    Candida glabrata
    Trichomonas vaginalis Escherichia coli
    Staphylococcus aureus
    Group B Streptococcus
    Enterococcus faecalis