Bacterial vaginosis laboratory findings
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Bacterial vaginosis can be diagnosed by the use of clinical criteria (Amsel’s Diagnostic Criteria) or Gram stain. A Gram stain is considered the gold standard laboratory method for diagnosing bacteria vaginosis.[1]
Laboratory Findings
In clinical practice, the diagnosis of bacterial vaginosis is based on the presence of at least three Amsel criteria on laboratory studies.[1] Vaginal swabs following speculum examination will be tested for:
- Whiff test: A small amount of an alkali is added to a microscope slide that has been swabbed with the discharge—a “fishy” odor is a positive result for bacterial vaginosis.
- Loss of acidity: A swab of the discharge is put onto litmus paper to check the acidity. A positive result for bacterial vaginosis would be a pH>4.5 (normally slightly acidic with a pH of 3.8–4.2).
- Clue cells: epithelial cells coated with bacteria (under microscopic examination of the discharge)
In research studies, the use of Nugent or Hay/Ison criteria to evaluate a Gram-stained smear of vaginal discharge is the diagnostic standard.
Gram Stain
A Gram stain is considered the gold standard laboratory method for diagnosing bacteria vaginosis. It is used to determine the relative concentration of lactobacilli (Gram-positive rods), Gram-negative and Gram-variable rods and cocci (Gardnerella vaginalis, Prevotella, Porphyromonas, and peptostreptococci), and curved Gram- negative rods (Mobiluncus) which are characteristic of bacterial vaginosis.Gram staining is usually reserved for research studies and can be used with the Hay/Ison criteria or the Nugent criteria.[1][2]
Hay/Ison Criteria
The Hay/Ison criteria are defined as follows: [3][4]
| Grading | Definition |
|---|---|
| Grade 0 | No bacteria present |
| Grade 1 | Lactobacillus morphotypes predominate |
| Garde 2 | Mixed flora with (some lactobacilli, gardnerella,or mobiluncus morphotypes present) |
| Garde 3 | Predominantly gardnerella and/or mobiluncus morphotypes (few or absent lactobacilli) |
| Garde 4 | Gram-positive cocci predominate |
- Grade 3 is diagnostic
Nugent Criteria
The standard for research are the Nugent Criteria.[5]
| Score | 0 | 1 | 2 | 3 | 4 |
|---|---|---|---|---|---|
| Lactobacillus morphotypes | >30 | 15-30 | <14 | <1 (this is an average) | 0 |
| Gardnerella/Bacteroides morphotypes | 0 | <1 (this is an average) | 1-4 | 5-30 | >30 |
| Curved Gram variable rods | 0 | <5 | >5 |
In this scale a score of 0-10 is generated from combining three other scores. It is time consuming and requires trained staff but is has high interobserver reliability:
- 0–3 is considered negative for bacterial vaginosis
- 4–6 is considered intermediate
- 7+ is considered indicative of bacterial vaginosis
Cytology
The Papanicolaou smear is not reliable for diagnosis of bacterial vaginosis.[6]
Culture
Vaginal culture has no role in diagnosis of bacterial vaginosis. [1][7]
References
- ↑ 1.0 1.1 1.2 1.3 Center for Disease Control and prevention. Mortality and morbidity weekly reports. Sexually transmitted disease treatment guideline. (2015) https://www.cdc.gov/std/tg2015/tg-2015-print.pdf Accessed on October 20, 2016
- ↑ Nugent RP, Krohn MA, Hillier SL (1991). “Reliability of diagnosing bacterial vaginosis is improved by a standardized method of gram stain interpretation”. J Clin Microbiol. 29 (2): 297–301. PMC 269757. PMID 1706728.
- ↑ Guideline Clearing House. “2002 national guideline for the management of bacterial vaginosis”. Unknown parameter
|http://www.guideline.gov/summary/summary.aspx?ss=ignored (help) - ↑ Ison, CA; Hay, PE (2002), “Validation of a simplified grading of Gram stained vaginal smears for use in genitourinary medicine clinics”, Sex Transm Infect, 78: 413–415
- ↑ Nugent, R. P., M. A. Krohn, and S. L. Hillier (1991). “Reliability of diagnosing bacterial vaginosis is improved by a standardized method of Gram stain interpretation”. J. Clin. Microbiol. 29: 297&ndash, 301.
- ↑ Greene JF, Kuehl TJ, Allen SR (2000). “The papanicolaou smear: inadequate screening test for bacterial vaginosis during pregnancy”. Am J Obstet Gynecol. 182 (5): 1048–9. PMID 10819823.
- ↑ Stockdale CK (2016). “A Positive Culture Result for Gardnerella Is Not Diagnostic of Bacterial Vaginosis”. J Low Genit Tract Dis. 20 (4): 281–2. doi:10.1097/LGT.0000000000000237. PMID 27428605.
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