Bacterial vaginosis laboratory findings
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
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Overview
Laboratory Findings
In clinical practice, the diagnosis of bacterial vaginosis is based on the presence of at least three Amsel criteria. Usually vginal 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' odour 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 Satin
Gold standard for diagnosis of bacterial vaginosis is Garm stain vaginal discharge.[1]
Cytology
The Papanicolaou smear is not reliable for diagnosis of bacterial vaginosis.[2]
Culture
Vaginal culture has no role in diagnosis of bacterial vaginosis.
Electrolyte and Biomarker Studies
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' odour 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)
Diagnostic Criteria
Amsel Criteria
In clinical practice bacterial vaginosis (BV) is diagnosed using the Amsel criteria:[3]
- Thin, white, yellow, homogeneous discharge
- Clue cells on microscopy
- pH of vaginal fluid >4.5
- Release of a fishy odor on adding alkali—10% potassium hydroxide (KOH) solution.
At least three of the four criteria should be present for a confirmed diagnosis.[4]
Hay/Ison Criteria
An alternative is to use a Gram stained vaginal smear, with the Hay/Ison[5] criteria or the Nugent[6] criteria. The Hay/Ison criteria are defined as follows: [4]
- Grade 1 (Normal): Lactobacillus morphotypes predominate.
- Grade 2 (Intermediate): Mixed flora with some Lactobacilli present, but Gardnerella or Mobiluncus morphotypes also present.
- Grade 3 (Bacterial Vaginosis): Predominantly Gardnerella and/or Mobiluncus morphotypes. Few or absent Lactobacilli. (Hay et al., 1994)
What this technique loses in interobserver reliability, it makes up in ease and speed of use.
Nugent Criteria
The standard for research are the Nugent[6] Criteria. 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:
| 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 |
- 0–3 is considered negative for BV
- 4–6 is considered intermediate
- 7+ is considered indicative of BV.
At least 10–20 high power (1000× oil immersion) fields are counted and an average determined.
| 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 |
References
- ↑ 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.
- ↑ 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.
- ↑ Amsel, R; Totten, PA; Spiegel, CA; Chen, KC; Eschenbach, D; Holmes, KK (1983), "Nonspecific vaginitis. Diagnostic criteria and microbial and epidemiologic associations", Am J Med, 74: 14–22
- ↑ 4.0 4.1 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
- ↑ 6.0 6.1 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.