Did you know?
The Nugent Score is widely used in microbiome research, especially in studies on pregnancy and STI risks? Research has linked high Nugent Scores (7–10) to increased risks of preterm birth, pelvic inflammatory disease, and HIV susceptibility.
Nugent Score
Researched by:
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Divine Aleru
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Divine Aleru
I am a biochemist with a deep curiosity for the human microbiome and how it shapes human health, and I enjoy making microbiome science more accessible through research and writing. With 2 years experience in microbiome research, I have curated microbiome studies, analyzed microbial signatures, and now focus on interventions as a Microbiome Signatures and Interventions Research Coordinator.
The Nugent Score is a standardized Gram stain-based scoring system used to diagnose bacterial vaginosis (V) by assessing key bacterial morphotypes in vaginal samples. With its high specificity, it remains a gold standard in microbiome research, though its complexity and need for trained personnel make it less common in routine clinical practice.
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Divine Aleru
Researched by:
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Divine Aleru
ID
Divine Aleru
Microbiome Signatures identifies and validates condition-specific microbiome shifts and interventions to accelerate clinical translation. Our multidisciplinary team supports clinicians, researchers, and innovators in turning microbiome science into actionable medicine.
Divine Aleru
Overview Overview
The Nugent Score is a microscopic diagnostic method used to identify bacterial vaginosis (BV) by evaluating the presence of specific bacterial morphotypes in Gram-stained vaginal swabs. This method, developed by Robert P. Nugent in 1991, offers a structured approach to assess the balance of Lactobacillus and BV-associated bacteria without the need for culture-based techniques.
How the Nugent Score Works
The Nugent scoring system evaluates bacterial vaginosis (BV) by quantifying bacterial morphotypes under a 1000× oil immersion microscope across multiple fields. It assesses three key morphotypes: Lactobacillus (large Gram-positive rods), which dominate in a healthy vaginal microbiome; Gardnerella vaginalis and Bacteroides (small Gram-variable rods), which increase in BV cases; and Mobiluncus (curved Gram-variable rods), which are associated with more severe BV. Each morphotype is scored based on its abundance, and the total score—ranging from 0 to 10—determines BV status: 0–3 indicates a healthy microbiota, 4–6 is considered intermediate, and 7–10 confirms a BV diagnosis characterized by reduced Lactobacillus and elevated BV-associated bacteria.
Advantages and Limitations of the Nugent Score
The Nugent Score offers a highly specific, objective assessment of bacterial vaginosis (BV) by quantifying bacterial morphotypes via Gram-stained microscopy, reducing diagnostic subjectivity compared to Amsel’s Criteria. While it plays a critical role in research on pregnancy outcomes, STI susceptibility, and treatment efficacy, its labor-intensive nature—requiring oil immersion microscopy and trained analysis—limits its use in clinical settings. In practice, providers often prefer the faster, though more subjective, Amsel’s Criteria for point-of-care diagnosis. Despite its declining clinical use, the Nugent Score remains a cornerstone in vaginal microbiome and epidemiological research.
Comparison to Amsel’s Criteria
The Nugent Score and Amsel’s Criteria are two diagnostic methods for bacterial vaginosis (BV), each with distinct features. The Nugent Score relies on Gram stain-based microscopic evaluation of bacterial morphotypes, offering a standardized and objective assessment but requiring specialized equipment and trained personnel. It is more time-consuming and primarily used in research settings. In contrast, Amsel’s Criteria are based on clinical signs—vaginal discharge, pH >4.5, clue cells on wet mount, and a positive whiff test—allowing for rapid, bedside diagnosis without specialized tools. Due to its ease of use and speed, Amsel’s Criteria is more commonly employed in routine clinical practice, despite its greater subjectivity.
| Feature | Nugent Score | Amsel’s Criteria |
|---|---|---|
| Diagnostic Basis | Gram stain bacterial evaluation | Clinical signs (discharge, pH, clue cells, odor) |
| Time Required | Longer (Microscopic evaluation) | Quick (Bedside diagnosis) |
| Lab Equipment | Requires trained microscopist | No special equipment needed |
| Use in Practice | More common in research | More commonly used in clinics |
Bacterial Vaginosis
Bacterial vaginosis (BV) is caused by an imbalance in the vaginal microbiota, where the typically dominant Lactobacillus species are significantly reduced, leading to an overgrowth of anaerobic and facultative bacteria.