Intrasubject test-retest variability in clinical electrocochleography

Seventeen healthy volunteers without a history of auditory or vestibular difficulty and with normal screening audiometry had bilateral (34 ears) electrocochleography performed repeatedly at 1-week intervals. Each subject had from four to seven electrocochleograms performed on each ear. Measurements were made in the external auditory canal using a gold-foil "TIPtrode." Amplitude and latency for the summating potential (SP) and action potential (AP) were measured and SP/AP ratios were calculated. Averages and standard deviations for amplitude, latency, and SP/AP ratios were computed. The average SP/AP ratio was 0.22 with a standard deviation of 0.06. The range was 0.04 to 0.50. The average difference between the highest and lowest SP/AP ratio for a given individual was 0.155 (i.e., the range 0.03 to 0.31) with a standard deviation of 0.07. These normative data are useful in assessing the results of dehydration electrocochleography and in establishing how much test-retest variation is required to suggest pathology.