Comparison of Distortion-Product Otoacoustic Emissions Measured in the Same Subjects Using Four Commercial Systems

Background/Objectives: Distortion-product otoacoustic emissions (DPOAEs) are suited to longitudinal cochlear assessment, but inter-system differences may confound interpretation across clinics. This study compared DPOAE outcomes across four commercial systems and evaluated their within-session repeatability. Methods: Adults with normal hearing (84 ears) were tested using the HearID DP (Mimosa Acoustics), SmartDPOAE (Intelligent Hearing Systems), Eclipse DPOAE20 (Interacoustics), and Echoport ILO 292 USB I (Otodynamics). DPOAEs were recorded at 1, 1.5, 2, 3, 4, 6 and 8 kHz using a criterion of ≥6 dB signal-to-noise ratio. Two measurements per ear were obtained, with the probe repositioned between sessions. Results: All systems showed similar frequency response profiles but substantially different absolute values. Between-system amplitude differences were smallest at 1.5–4 kHz and largest at 6 kHz. Noise floors varied considerably: HearID DP and SmartDPOAE were best (lowest) while Echoport ILO 292 USB I and Eclipse DPOAE20 were worst (highest), with inter-system differences most prominent between 1.5 and 4 kHz. HearID DP achieved the highest detection rates (84/84 ears at key frequencies). Test–retest reliability was good across all systems. The standard error of measurement varied from 0.99 to 2.88 dB, the smallest being the HearID DP. Within-session differences were typically ≤2 dB, with the best repeatability between 1.5 and 6 kHz. Conclusions: Despite similar frequency responses, clinically significant differences exist between DPOAE systems in terms of noise floors, signal-to-noise ratios, and response amplitudes. Inter-device variations frequently exceeded minimum detectable change values, meaning that DPOAE devices cannot be considered clinically interchangeable. These findings underscore the need for industry-wide standards to enable reliable cross-clinic comparisons.