Understanding the Nugent Score for BV Diagnosis

The Nugent Score is a method of determining bacterial vaginosis based on how many groups of bacteria exist, using swabs.

How the Nugent score is determined

The test seeks to get a score out of 10, finding the indicators (rods) of lactobacilli, Gardnerella vaginalis, and Mobiluncus spp.

Large gram-positive rods – lactobacilli species, a decrease scored as 0 to 4
Small gram-positive rods – Gardnerella vaginalis morphotypes, scored as 0 to 4
Curved gram-variable rods – Mobiluncus spp. morphotypes, scored as 0 to 2 (may include Mycoplasma and other curved gram-variable rods)

A score of 7 to 10 is consistent with bacterial vaginosis, without a culture being taken.

Nugent scoring details

Lactobacillus (avg. per high powered 1000x oil immersion field) score 0-4

Score 0 for >30
Score 1 for 15–30
Score 2 for 14
Score 3 for <1 (this is an average, so results can be >0, yet <1)
Score 4 for 0

Gardnerella / Bacteroides (avg. per high powered 1000x oil immersion field) score 0-4

Score 0 for 0
Score 1 for <1 (this is an average, so results can be >0, yet <1)
Score 2 for 1–4
Score 3 for 5–30
Score 4 for >30

Curved gram-variable rods (avg. per high powered 1000x oil immersion field) score 0-2

Score 0 for 0
Score 1 for <5
Score 2 for 5+

About the Nugent scoring system

It is used less and less due to its time-consuming nature, and has been criticised as being a ‘fallacy of proportional logic’. A trained microscopist must be present to determine the presence of various microbe indicators. This means it is useful in scientific research, because it is easy to replicate. There are issues in determining a patient’s BV status based on this method, since in poorer areas, access to the resources required for this come at a cost. Microscopes with large enough viewing areas, highly trained staff, and the facilities all come at a premium that many aren’t willing to invest in. This makes the need for a cheaper, faster, better system a priority.

The proposed three-way system

It was proposed that the Nugent score should be divided into three subgroups so as to differentiate between the different lactobacilli species, however so far this hasn’t been taken up across the board.

Other systems for diagnosing BV

The Amsel criteria are also used, but the processes are not comparable to each other, making it less useful in a comparison. The Ison/Hay method is also used.