Bacterial Vaginosis Workup

  • Author: Diana Curran, MD, FACOG; Chief Editor: Michel E Rivlin, MD   more...
 
Updated: Apr 12, 2012
 

Laboratory Studies

  • Clinical diagnosis of bacterial vaginosis (BV) relies on history, vaginal examination, and microscopic examination (see the Table for a summary of the differential diagnoses). Emerging data support sending vaginal cultures in recalcitrant cases.[7]
  • Historical information regarding the patient's symptoms and nature of the discharge
    • Most patients experience a vaginal malodor and/or an increase in vaginal discharge.
    • Vulvar irritation may be present or absent.
    • Dysuria, dyspareunia, and abdominal pain are lacking.
  • Vaginal examination
    • Typical BV discharge characteristics
    • Lack of significant vulvovaginal inflammation
  • Microscopic examination of the discharge: Demonstrating 3 of the following 4 Amsel's criteria is considered necessary to diagnose BV most accurately.[8]
    • Demonstration of clue cells on a saline smear is the most specific criterion for diagnosing BV. Clue cells are vaginal epithelial cells that have bacteria adherent to their surfaces. The edges of the squamous epithelial cells, which normally have a sharply defined cell border, become studded with bacteria. The epithelial cells appear to be peppered with coccobacilli.
    • A pH greater than 4.5 indicates infection, and pH may be elevated in up to 90% of patients with BV.
    • Characteristic discharge appearance is thin, gray, and homogeneous.
    • The whiff test may be positive in up to 70% of BV patients. This test is performed by placing a drop of 10% KOH on the speculum after the vaginal examination or mixing vaginal fluid with a drop of KOH on a microscope slide. The KOH, by virtue of its alkaline properties, causes the release of volatile amines from the vaginal fluid. The amines are products of anaerobic bacterial metabolism.
  • The bacterial flora may be examined microscopically for evidence of changes in the overall bacterial predominance. The healthy vagina has a predominance of lactobacilli (large gram-positive rods). The flora of a patient with BV changes to become dominated by coccobacilli, reflecting an increase in the growth of Gardnerella vaginalis and other anaerobes.
    • Many use Nugent's criteria to quantify or grade bacteria via gram stain of vaginal samples. In brief, Nugent's criteria evaluate 3 types of bacteria via gram stain: Lactobacillus, Bacteroides/Gardnerella, and Mobiluncus. They are each graded on a scale of 1-4 (1+ is < 1 cell per field, 2+ is 1-5 cells per field, 3+ is 6-30 cells per field, and 4+ is >30 cells per field). In this system, Lactobacillus and Bacteroides/Gardnerella are given scores between 0-4 but Mobiluncus is only graded from 0-2. Total scores are then calculated and used as follows: 0-3 (Normal), 4-6 (intermediate bacterial count), and 7-10 (bacterial vaginosis).[9]
  • The vaginal discharge of patients with BV is notable for its lack of polymorphonuclear leukocytes (PMNs), typically 1 or less than 1 PMN per vaginal epithelial cell.
  • Diagnosing BV accurately is more difficult when a coinfection is present. However, finding an increase in the number of PMNs per epithelial cell may lead the clinician to consider BV as a possibility.
  • Obtaining routine vaginal cultures in patients with BV has no utility because this is a polymicrobial infection and some women may have asymptomatic carriage of G vaginalis organisms. Although G vaginalis has been demonstrated to grow in up to 100% of vaginal cultures of women with BV, it has also been cultured in up to 70% of asymptomatic women. However, obtaining cultures to exclude other infectious etiologies (eg, Trichomonas species, C trachomatis, N gonorrhoeae) is appropriate. In recurrent cases that have not resolved with standard regimens, cultures may be appropriate.
  • A more recent diagnostic tool is FemExam (CooperSurgical, Inc, Trumbull, CT)[10] , which has been shown to have variable sensitivity (38-90%) and specificity (12.5-97%) depending on the study and study population (pre- vs postmenopausal).[11] The test provides a result in 2 minutes.
  • Other diagnostic tools use DNA extracted from samples of vaginal fluid using Instagene Matrix (Bio-Rad Laboratories, Hercules, CA). Results of these tests often show a difference in the bacterial components in women with BV who are postmenopausal compared with those who are premenopausal. This information is certainly helpful, particularly in treatment failures to better tailor antibiotic treatment.[11]

Table. Differential Diagnosis of the Vaginitides (Open Table in a new window)

Clinical ElementsBacterial VaginosisTrichomoniasisVaginal Candidiasis
SymptomsVaginal odor++/--
Vaginal dischargeThin, gray, homogenousGreen-yellowWhite, curdlike
Vulvar irritation+/-++
Dyspareunia-+-
SignsVulvar erythema-+/-+/-
Bubbles in vaginal fluid++/--
Strawberry cervix-+/--
MicroscopySaline wet mount
Clue cells+--
Motile protozoa-+-
KOH test
Pseudohyphae--+
Whiff test++/--
pH>4.5>4.5< 4.5
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Procedures

No other procedures are necessary in the evaluation of patients with BV other than those listed in Lab Studies.

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Contributor Information and Disclosures
Author

Diana Curran, MD, FACOG  Assistant Professor, Residency Program Director, Department of Obstetrics and Gynecology, University of Michigan Health Systems

Diana Curran, MD, FACOG is a member of the following medical societies: American College of Obstetricians and Gynecologists, American Medical Association, and Central Association of Obstetricians and Gynecologists

Disclosure: Nothing to disclose.

Specialty Editor Board

Thomas Michael Price, MD  Associate Professor, Division of Reproductive Endocrinology, Director of Reproductive Fellowship Training Program, Duke University Medical Center

Thomas Michael Price, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Obstetricians and Gynecologists, American Medical Association, American Society for Reproductive Medicine, Association of Professors of Gynecology and Obstetrics, Endocrine Society, Phi Beta Kappa, Society for Gynecologic Investigation, Society for Reproductive Endocrinology and Infertility, and South Carolina Medical Association

Disclosure: Clinical Advisors Group Consulting fee Consulting; MEDA Corp Consulting Consulting fee Consulting; Gerson Lehrman Group Advisor Consulting fee Consulting; Adiana Grant/research funds PI

Francisco Talavera, PharmD, PhD  Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

A David Barnes, MD, PhD, MPH, FACOG  Consulting Staff, Department of Obstetrics and Gynecology, Mammoth Hospital (Mammoth Lakes, California), Pioneer Valley Hospital (Salt Lake City, Utah), Warren General Hospital (Warren, Pennsylvania), and Mountain West Hospital (Tooele, Utah)

A David Barnes, MD, PhD, MPH, FACOG is a member of the following medical societies: American College of Forensic Examiners, American College of Obstetricians and Gynecologists, American Medical Association, Association of Military Surgeons of the US, and Utah Medical Association

Disclosure: Nothing to disclose.

Frederick B Gaupp, MD  Consulting Staff, Department of Family Practice, Hancock Medical Center

Frederick B Gaupp, MD is a member of the following medical societies: American Academy of Family Physicians

Disclosure: Nothing to disclose.

Chief Editor

Michel E Rivlin, MD  Professor, Department of Obstetrics and Gynecology, University of Mississippi School of Medicine

Michel E Rivlin, MD is a member of the following medical societies: American College of Obstetricians and Gynecologists, American Medical Association, Mississippi State Medical Association, and Royal College of Surgeons of Edinburgh

Disclosure: Nothing to disclose.

Additional Contributors

The authors and editors of eMedicine gratefully acknowledge the contributions of previous authors Eric A Hansen, DO and Burke A Cunha, MD to the development and writing of this article.

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Table. Differential Diagnosis of the Vaginitides
Clinical ElementsBacterial VaginosisTrichomoniasisVaginal Candidiasis
SymptomsVaginal odor++/--
Vaginal dischargeThin, gray, homogenousGreen-yellowWhite, curdlike
Vulvar irritation+/-++
Dyspareunia-+-
SignsVulvar erythema-+/-+/-
Bubbles in vaginal fluid++/--
Strawberry cervix-+/--
MicroscopySaline wet mount
Clue cells+--
Motile protozoa-+-
KOH test
Pseudohyphae--+
Whiff test++/--
pH>4.5>4.5< 4.5
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