The diagnosis of Noise Induced Hearing Loss (NIHL) is critical in medicolegal cases, where accurate diagnoses are essential. 

A recently published article provides an initial overview of a paper* by Lutman, de Carpentier & Green which investigates the specificity of the 2022 MLC (Moore, Lowe and Cox) guidelines compared to the established CLB (Coles, Lutman and Buffin) guidelines for diagnosing NIHL. 

Specificity “refers to the accuracy with which true negative cases … are identified correctly” and there are concerns that the MLC guidelines “may have unacceptably poor specificity”. “Poorer specificity is often described as an increased false-positive rate”.

Against that backdrop, the study applied the MLC guidelines and CLB guidelines to three data sets of audiological results. These each being cohorts of people where there was no significant or material noise exposure reported. As there has been no noise exposure there should be no NIHL diagnosis under the guidelines. The authors found that the MLC guidelines allowed for a far higher number of false positive results than the previous CLB guidelines.

For the procedure applicable to steady broadband noise exposure within the MLC guidelines, the false positive rate averaged 56% in the population samples, compared to 31% for the CLB guidelines. For exposure to intense impulse sounds the false positive rate was 70%. For exposure to intense tones the false positive rate reached 80%.

The paper suggests that even the false positive rate of about 30% for the CLB guidelines is arguably too high. They suggest that increasing the notch/bulge requirement from 10 to 15 dB would decrease the false positive rate by about 10 percentage points. This comment is particularly noteworthy, and it will be interesting to see if it is taken into consideration in cases going forward.

The paper in particular criticises the MLC guidelines for a lack of guidance on how to deal with cases where hearing loss is asymmetrical. It also found that the MLC guidelines lack of correction at 6kHz when TDH-39 earphones are used, increases false positive rates by about 20%. 

Finally, it concludes by stating that “The utility of guidelines that produce high false positive rates in a medicolegal context is questionable.” 

It will be interesting to see how these findings are interpreted going forward.

*The published has noted that paper “is a preprint and has not been peer reviewed. Data may be preliminary.”