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Amsel Criteria

Editor: Michael Steelman Updated: 7/4/2023 12:37:12 AM


Bacterial vaginosis has universal acknowledgment as the most prevalent cause of vaginal disorders in women of reproductive age, present in an estimated 10 to 20% of White women and 30 to 50% of Black women.[1] Estimates for the exact percentage of women afflicted at any one time vary from as low as 5% to as high as 70% worldwide.[2] If symptomatic, patients often complain of vaginal discharge having a classic "fishy" odor; however, many women remain asymptomatic until detection during a routine vaginal exam or pap smear.[3] Unfortunately, leaving bacterial vaginosis untreated provides an opportunity for several complications, including inflammation of endometrial or cervical tissue, urinary tract infection, chronic pelvic pain, increased risk of HIV and other STDs, and elevated risk of ectopic pregnancy as well as difficult conception.[4] As pertains to pregnancy, consequences may be even more severe and include the potential for prematurity of the newborn, premature rupture of membranes, and low birth weight.[5]

Treatment for this issue generally involves antibiotic therapy via intravaginal gel or oral pill. Metronidazole or clindamycin are the most commonly used antimicrobial agents. Unfortunately, the complete cure rate for bacterial vaginosis is between 65 to 85 percent, and many women experience a relapse in the weeks or months following treatment.[6]

The Nugent scoring system had previously been considered the gold standard for the diagnosis of bacterial vaginosis. This system, discovered by RP Nugent and published in 1991, added more specific qualifications to the previous gold standard, the Spiegel criteria - otherwise known as Gram staining of vaginal smears. Using the Nugent score, vaginal smears are plated on a microscopic slide in oil immersion, and a minimum of 10 high power fields are examined for three bacteria morphotypes: Lactobacillus, Gardnerella, and curved gram rods. Each of these three categories receives a score based on the number of bacteria counted. Subsequently, these three scores are added together for a total score ranging from 0 - 10. The scoring is as follows[7]:

  • 0–3: negative for BV
  • 4–6: intermediate
  • 7+: positive for BV

While accurate, the Nugent scoring system has been disregarded by many physicians as cumbersome due to the skill level required with microscopy as well as the time it takes to physically perform bacteria counts. The Amsel criteria have, by and large, replaced the Nugent system.

The Amsel criteria, originally published in the American Journal of Medicine in 1983, provides a more accessible, clinically defined basis for the diagnosis of bacterial vaginosis using only four criteria. Though older and seemingly simpler, the Amsel criteria have been validated as equivalent to Nugent scoring when diagnosing bacterial vaginosis.[8] It is generally preferred for its ease and ability to be performed using only basic observational microscopic techniques.


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The Amsel criteria are in the diagnosis of bacterial vaginosis. It is considered particularly helpful during situations in which the diagnostician's microscopic experience, availability of microscope tools, or time may be a limiting factor.  There are four parameters used to determine the presence or absence of BV. These are:

  • Thin, white, yellow, homogeneous discharge
  • Clue cells on wet mount microscopy
  • a vaginal fluid pH of  over 4.5 when placing the discharge on litmus paper
  • Release fishy odor after adding 10% potassium hydroxide (KOH) solution to wet mount - also known as “whiff test.”

Three of the four above criteria must be present to confirm the diagnosis,[9] although some updated literature allows for modification of the criteria to only include two of the four to achieve a positive test.

Issues of Concern

One particular issue of concern with the Amsel criteria is that, although the required microscopy is less complicated, it does still require the competent use of a microscope to identify clue cells. While most diagnosticians should be able to perform basic microscopic exams without much difficulty, those who have visual limitations or little/distant experience in using microscopy may be at a disadvantage. Those without microscopes entirely are unable to perform this test.

Additionally, the Amsel criteria do require the retrieval of vaginal discharge sampling. While this generally can be done without much patient discomfort, some providers may feel inclined to accept the patient’s report of symptoms such as discharge or fish smell as a positive criterion without collecting physical samples instead. It is important to note that in the context of the Amsel criteria, the “whiff test” is only considered positive after applying potassium hydroxide solution to the vaginal sample on a wet mount. Patient report of fish smelling discharge does not constitute a positive whiff test, and therefore may not be considered a positive criterion.

Moreover, as mentioned above, it has been suggested that the Amsel criteria, while an improvement on Nugent scoring, should be further simplified to require only two out of four criteria to be considered a positive test. One study, in particular, found that using a combination of any two positive Amsel criteria had 99 to 100% specificity - and, in fact, the presence of clue cells on their own was 98% specific and 89.9% sensitive for bacterial vaginosis.[10]  This fact suggests that there is room to update and further simplify the Amsel criteria while still providing accurate results. 

Conversely, it is essential to note that while the specificity of the Amsel criteria has general regard for achieving the 99th percentile, reports of sensitivity vary widely, with some studies reporting a sensitivity of only 37%.[11]  There is no known explanation for this discrepancy.

Clinical Significance

The Amsel criteria are useful in the outpatient setting. The presence of three out of four positive criteria indicates that the cause of a patient’s vaginal complaints is bacterial vaginosis.  Use of the Amsel criteria requires a vaginal swab of discharge, microscope and slide/wet prep, and potassium hydroxide solution. The Amsel criteria allow diagnosticians to narrow down the broad differential for vaginal discharge and discomfort with quick and simple testing.

Other Issues

As stated above, the Amsel criteria is currently a set of four parameters. However, updated studies suggest the exact number needed to diagnose bacterial vaginosis accurately may be able to be further narrowed down.

It is important to note that in recent years, other diagnostic methods have been under investigation, though there is not yet sufficient evidence to call one of these a new gold standard. Several new methods are being researched, including DNA hybridization and several variants of polymerase chain reaction.[12][13][14]

Enhancing Healthcare Team Outcomes

Bacterial vaginosis is an incredibly common cause of vaginal disorders in women of reproductive age.  Patients with these complaints often present with only a vague sign or symptom, such as vaginal discomfort.  The cause of vaginal discomfort poses a broad differential diagnosis, including abdominal, pelvic, or urinary tract causes.  It is imperative that this pathology is detected and treated to prevent future complications, particularly in pregnancy. 

The family practitioner, nurse practitioner, or gynecologist is often the first line in dealing with cases of vaginal discomfort, yet it is crucial to include other members of the patient care team such as nursing, medical assistants, and obstetricians. An interprofessional approach is optimal in serving patients in this regard; obstetricians, gynecologists, pediatricians, and family practitioners should keep bacterial vaginosis in mind when patients complain of vaginal symptoms.  Patients sometimes find it easier to report symptoms to a familiar or "less intimidating" health professional.  Nurses and medical assistants are vital in this regard and should pay attention to the patient's list of concerns and report pertinent complaints to the provider.

Afflictions involving changes to vaginal secretions can be embarrassing, and should receive treatment quickly and with the minimum invasiveness required. The Amsel criteria should be employed to allow for efficient and straightforward diagnosis to decrease the prevalence of bacterial vaginosis and its numerous potentially more severe complications.  The USPTF does not at this time recommend screening for asymptomatic or low-risk women [Category D]; however, when suspicion is high, the Amsel criteria are recommended as the diagnostic tool of choice.  When detected and adequately treated, the cure rate can reach as high as 80%, preventing further serious complications.[15] [Level 3]

Nursing, Allied Health, and Interprofessional Team Interventions

Nursing alone cannot be responsible for employing the Amsel criteria. Useful participation from nursing would include making a slide, KOH, and swab available, along with a speculum and gown for all patients who present with vaginal discharge complaints.

Nursing, Allied Health, and Interprofessional Team Monitoring

There is no required nursing monitoring involved in the Amsel criteria.[15]



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