Test–retest reliability and agreement of ear-canal and mastoid Wave I Auditory Brainstem Responses in healthy young adults

OBJECTIVE: This study evaluated the test-retest reliability of Wave I amplitude and latency and examined sources of variability, including head size, cardiac, respiratory parameters and tester effects. Wave I amplitude, a proposed biomarker of cochlear synaptopathy, requires established reproducibility. DESIGN: Thirty participants attended up to four sessions two weeks apart. Click-evoked ABRs were recorded at 80 dB nHL from ear-canal and mastoid electrodes, with ECG monitoring: three sessions by one tester, one by another. STUDY SAMPLE: Adults aged 18-25 years (19 women) with normal audiometric thresholds (Pure-Tone Average 500-4000 Hz < 20 dB HL) and normal speech-in-noise performance (signal-to-noise ratio [SNR] < -3 dB). RESULTS: An SNR-based quality threshold retained >80% of recordings. Reproducibility was higher for Ear-canal than Mastoid recordings (ICC [intraclass correlation coefficient] = 0.80 [95% CI: 0.61-0.88] vs. 0.77 [0.57-0.84]; CV [coefficient of variation] 12-14%). Latency showed excellent agreement (CV 2-3%). Adjusting amplitude for head size and residual noise reduced the central 95% range by 18%, although the distribution remained wide. Tester variance remained below residual within-ear variance. CONCLUSIONS: Wave I measures show good within-individual reproducibility, supporting longitudinal monitoring. Tester variance was not the dominant source of variability, and the SNR threshold and normalisation approach provide actionable tools for multi-tester studies.