Auditory Brainstem Response: Indicator of Hearing Loss

A new study has established the first clinically usable normative ranges for a key auditory brainstem response (ABR) measurement, providing a potential diagnostic tool for identifying cochlear deafferentation in patients with normal hearing tests. Published in the *American Journal of Audiology*, the research from the VA National Center for Rehabilitative Auditory Research offers a method to detect a “hidden” hearing loss that standard audiograms miss.

### Establishing a Baseline for Healthy Ears

The research team, led by Sean D. Kampel and Garnett P. McMillan, first needed to define what a “normal” ABR Wave I amplitude looks like. Wave I is the first major peak in the ABR, generated by the auditory nerve. A reduced amplitude is a strong indicator of cochlear synaptopathy—damage to the connections between inner hair cells and the auditory nerve—in animal models.

To create a reliable baseline, they recruited 169 non-Veteran young adults. This low-risk group had pristine audiograms, reported minimal history of noise exposure, and had no complaints of tinnitus, decreased sound tolerance (hyperacusis or misophonia), or difficulty understanding speech in noise. The researchers measured each participant’s ABR Wave I amplitude in response to tonebursts at 2, 4, and 8 kHz. They then generated statistical normative ranges, adjusting for biological sex and, initially, for distortion product otoacoustic emission (DPOAE) levels, which reflect outer hair cell health.

### Testing the Ranges on a High-Risk Population

With the normative ranges established, the next step was to test their diagnostic power. The high-risk comparison group consisted of 91 military Veterans. Like the low-risk group, all Veterans had normal pure-tone audiograms. Unlike the control group, every Veteran reported at least one persistent auditory complaint, such as tinnitus, hyperacusis, or speech-in-noise difficulties. This population is considered at high risk for cochlear deafferentation due to likely histories of significant noise exposure during service.

The researchers compared the Veterans’ ABR Wave I amplitudes to the two sets of normative ranges: one adjusted for both sex and DPOAE levels, and one adjusted for sex alone.

### A Simpler Method Proves More Effective

The results held a significant and practical finding. While both sets of ranges could distinguish between the low- and high-risk groups, the analysis revealed that adjusting for DPOAEs might be counterproductive. Since DPOAEs measure outer hair cell function and Wave I amplitude reflects inner hair cell/nerve health, conflating the two could mask the true neural deficit.

The sex-only adjusted normative ranges proved to be a robust and simpler tool. For a 105 dB peak equivalent SPL 8-kHz toneburst—a frequency often vulnerable to noise damage—51% of the high-risk Veteran sample fell below the normal range. This indicates a high prevalence of probable cochlear deafferentation in this symptomatic group with normal audiograms. The study’s authors conclude that “sex-specific ABR Wave I amplitude normative ranges can be used by clinicians to identify patients with high degrees of cochlear deafferentation.”

### Implications for Clinical Practice and Patient Understanding

This research, accessible via DOI: 10.1044/2026_AJA-25-00296 (PMID: 42635501), moves the field from theory to application. For clinicians, it provides a validated, objective protocol to investigate the biological basis of “invisible” auditory disorders. A patient presenting with tinnitus or hyperacusis but a normal audiogram could now undergo an ABR test to see if cochlear deafferentation is a contributing factor.

For patients, this work validates their experiences. It offers a potential physiological explanation for why they struggle with sound processing or perceive phantom noises despite being told their hearing is “normal.” Identifying deafferentation can steer management strategies, such as auditory training or targeted counseling, and inform critical hearing protection advice to prevent further neural loss.

The study also simplifies the path forward. By showing that a sex-adjusted ABR, without complex DPOAE corrections, is effective, it makes the test more feasible for widespread clinical adoption. This method could become a standard part of the diagnostic workup for auditory processing complaints, bridging a long-standing gap between patient symptoms and measurable pathology. Future research may explore how these ABR findings correlate directly with the severity of conditions like misophonia or speech-in-noise deficits, creating a more complete picture of hidden hearing loss.