What are the key diagnostic criteria for bacterial vaginosis in adult women presenting with vaginal discharge?

Guideline-aligned answer with reasoning, red flags and references. Clinically reviewed by Dr Kola Tytler MBBS CertHE MBA MRCGP.

Posted: 16 August 2025Updated: 16 August 2025 Guideline-Aligned (High Confidence) Clinically Reviewed
Dr Kola Tytler MBBS CertHE MBA MRCGPClinical Lead • iatroX

Key diagnostic criteria for bacterial vaginosis (BV) in adult women presenting with vaginal discharge include clinical and laboratory findings. Clinically, BV is suspected in women with a characteristic vaginal discharge that is typically thin, homogenous, and greyish-white, often accompanied by a fishy odour, especially after intercourse. The discharge is usually non-irritative and without significant inflammation or soreness .

Diagnostic confirmation involves a combination of clinical assessment and laboratory tests. The Amsel criteria, widely used in clinical practice, require at least three of the following four findings: (1) a thin, homogenous vaginal discharge; (2) vaginal pH greater than 4.5; (3) a positive whiff test (fishy odour on addition of 10% potassium hydroxide to vaginal secretions); and (4) the presence of clue cells on microscopic examination of vaginal fluid .

Microscopy is essential to identify clue cells, which are vaginal epithelial cells coated with bacteria, a hallmark of BV . Vaginal pH measurement is a simple point-of-care test that supports diagnosis, as BV typically raises vaginal pH above the normal acidic range .

While culture is not routinely used for diagnosis, it may be performed to exclude other infections if symptoms persist or diagnosis is uncertain . The UK guidelines emphasize that diagnosis should be based on clinical features supported by microscopy and pH testing rather than culture alone .

Recent literature concurs that BV diagnosis relies on clinical criteria supported by microscopy and pH testing, highlighting the importance of clue cells and elevated pH as key diagnostic markers . Molecular diagnostic methods are emerging but are not yet standard in primary care settings .

In summary, the key diagnostic criteria for BV in adult women with vaginal discharge are:

  • Characteristic thin, homogenous, greyish-white vaginal discharge with fishy odour
  • Vaginal pH >4.5
  • Positive whiff test (fishy odour on KOH addition)
  • Presence of clue cells on microscopy

These criteria should be used together to confirm diagnosis and guide appropriate management in general practice .

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