Clinically relevant long-term reliability of contralateral suppression of click evoked otoacoustic emissions

Background: Contralateral suppression of click-evoked otoacoustic emissions (CEOAEs) are a potentially useful clinical tool. Recent studies have provided descriptions of the reliability of contralateral suppression of CEOAEs. These were limited in terms of their clinical relevance as they utilised custom-built measurement systems or were conducted by a single tester over a short time period. Further, in the main previous studies reported only group data. The present study addresses these limitations by reporting individual and group data collected by two testers, using standard clinical equipment over longer time periods. Materials and methods: Contralateral suppression of CEOAEs was recorded from 12 ears using the ILO 292 system. Clicks and contralateral broadband noise (BBN) were presented at 60 dB p.e. SPL and 65 dB SPL respectively. Global and best ½-octave band suppression values (in dB) were measured on four separate occasions by two testers spanning an average time period of 35.5 days. Reliability was assessed via the intraclass correlation coefficient (ICC) and the standard error of measurement (SEm). Multilevel regression analysis was used to explore potential causes of variation in suppression. Results: Global suppression reliability was shown to be worse than previous reports, with only fair to good reliability observed. ICC and SEm values were 0.57 and 0.47 dB respectively. Corresponding values for best ½-octave band suppression were 0.49 and 0.64 dB. Further analysis revealed no significant effect on contralateral suppression for a range of variables tested. Substantial variation (up to 2 dB) in contralateral suppression between test sessions was seen for individual subjects. Conclusions: Findings suggest that contralateral suppression of CEOAEs, measured by separate testers using standard clinical equipment is not reliable over long time periods.