From the Guidelines
Bacterial vaginosis (BV) is diagnosed through a combination of clinical symptoms and laboratory tests, primarily using the Amsel criteria or Gram stain, as recommended by the U.S. Preventive Services Task Force 1.
Diagnostic Criteria
The diagnosis of BV can be made by fulfilling three of the four Amsel criteria:
- Thin, homogeneous vaginal discharge
- Vaginal pH greater than 4.5
- Positive whiff test (fishy odor when potassium hydroxide is added to vaginal secretions)
- Presence of clue cells on microscopic examination of vaginal fluid Alternatively, diagnosis can be made using Nugent scoring of a Gram-stained vaginal smear, with a score of 7-10 indicating BV 1.
Importance of Diagnosis
Proper diagnosis is crucial as BV increases the risk for sexually transmitted infections and can cause complications in pregnancy if left untreated 1. The condition represents an imbalance in vaginal flora, characterized by a decrease in normal lactobacilli and an overgrowth of anaerobic bacteria such as Gardnerella vaginalis and Prevotella species.
Screening and Treatment
Screening for BV in asymptomatic pregnant women is recommended, especially for those at high risk for preterm delivery 1. However, the optimal treatment regimen for pregnant women with BV is unclear, and treatment should be based on clinical judgment and current guidelines from the Centers for Disease Control and Prevention 1.
Key Points
- BV diagnosis is primarily clinical, using the Amsel criteria or Gram stain.
- Proper diagnosis is important to prevent complications, especially in pregnancy.
- Screening and treatment recommendations vary based on risk factors and clinical guidelines.
From the FDA Drug Label
For purposes of this indication, a clinical diagnosis of bacterial vaginosis is usually defined by the presence of a homogeneous vaginal discharge that (a) has a pH of greater than 4.5, (b) emits a “fishy” amine odor when mixed with a 10% KOH solution, and (c) contains clue cells on microscopic examination. A clinical diagnosis of bacterial vaginosis was based on Amsel's criteria and defined by the presence of an abnormal homogeneous vaginal discharge that (a) has a pH of greater than 4.5, (b) emits a "fishy" amine odor when mixed with a 10% KOH solution, and (c) contains ≥20% clue cells on microscopic examination.
To diagnose bacterial vaginosis, the following criteria should be used:
- Vaginal discharge: homogeneous and abnormal
- pH: greater than 4.5
- Odor: "fishy" amine odor when mixed with a 10% KOH solution
- Clue cells: presence of clue cells on microscopic examination, with ≥20% clue cells required for diagnosis in some cases 2, 3 A Gram stain of the vaginal smear can also be used to support the diagnosis, with characteristics including:
- Markedly reduced or absent Lactobacillus morphology
- Predominance of Gardnerella morphotype
- Absent or few white blood cells The Nugent score can also be used to quantify the bacterial morphotypes and determine the presence of bacterial vaginosis, with a score ≥4 indicating bacterial vaginosis and a score of 0 to 3 indicating a microbiologic cure 3.
From the Research
Diagnosis of Bacterial Vaginosis
To diagnose bacterial vaginosis, several methods can be employed, including:
- The Amsel criteria, which include vaginal pH greater than 4.5, positive whiff test, milky discharge, and the presence of clue cells on microscopic examination of vaginal fluid 4
- Gram stain, considered the diagnostic standard 5
- Newer laboratory tests that detect Gardnerella vaginalis DNA or vaginal fluid sialidase activity, which have similar sensitivity and specificity to Gram stain 5
- Nugent scoring system, although it is time consuming and costly, and its interpretation needs lab equipment and experts 6
Amsel Criteria
The Amsel criteria are commonly used for the diagnosis of bacterial vaginosis, with a sensitivity of 0.91, specificity of 0.91, positive predictive value of 0.86, negative predictive value of 0.94, and accuracy of 0.91 compared to the Nugent scoring system 6. However, the performance of the Amsel criteria can be poor in certain scenarios, such as when there is no use of a microscope, with a sensitivity of 22.8% 7.
Comparison of Diagnostic Methods
A comparison of the performance of different diagnostic methods for bacterial vaginosis found that:
- The Amsel criteria had a sensitivity of 41.3% and specificity of 97.8% 7
- Cultures had a sensitivity of 59.9% and specificity of 99.0% 7
- Wet mount microscopy (WMM) had a sensitivity of 82.6% and specificity of 92.4% 7 WMM performed equally well in symptomatic and asymptomatic women, and it is recommended as the first approach for the diagnosis of vaginitis 7.
Clinical Diagnosis
The clinical diagnosis of bacterial vaginosis can be evaluated using Amsel's criteria individually or in combinations of two, with sensitivity and specificity ranging from 83% to 93% and 82% to 94%, respectively 8. The accuracy of Amsel's clinical criteria individually or in combinations of two was as accurate as the presence of at least three criteria for the diagnosis of bacterial vaginosis 8.