Validity of impedance measurements and referral criteria in school hearing screening programmes

The increasing use of impedance methods in screening programmes for auditory dysfunction requires that the techniques and validity of the referral criteria be continually monitored. This research report describes one such study carried out as part of the normal school hearing test procedure. Comparative measurements were made using conventional pure tone sweep audiometry and with the 'Tympanometer' (American Electromedics 85 AR). Results are based on 423 ears from 9-year old juniors and 298 ears from 5-year old infants. Agreement between the two methods was obtained with 81% of the juniors and 74% of the infants. The majority of the disagreement resulted from the high sensitivity of the impedance system in detecting middle-ear disorders which did not result in a hearing loss detectable by a 20-dB sweep. Significantly, the Tympanometer missed two infants with moderate sensorineural losses. These false negatives relate directly to the Tympanometer reflex system which proved to be unreliable. The need for care in the selection of instrumentation is stressed.