Fixed-Level Frequency Threshold Testing for Ototoxicity Monitoring.

OBJECTIVES: Hearing loss from ototoxicity is often most pronounced at high frequencies. To improve patient monitoring and compliance, high-frequency testing methods should be short and easy to administer. We evaluated the repeatability and accuracy of a Békésy-like, fixed-level frequency threshold (FLFT) technique. This test takes less than a minute and could provide a rapid and effective way to determine the highest audible frequency. We hypothesized the FLFT test would be repeatable in normal-hearing subjects, and accurate when compared with Békésy fixed-frequency audiometry in the sensitive region for ototoxicity (SRO).
DESIGN: Twenty-nine normal-hearing subjects (20 females, 9 males) performed 2 different automated audiometry tests at least 4 times over a period of no less than 3 weeks. Ages ranged from 23 to 35 years (average = 28 years). Subjects completed testing under Sennheiser HDA-200 headsets. Initial fixed-frequency audiometry thresholds were obtained at frequencies ranging from 0.5 to 20 kHz to identify each subject's highest audible frequency, which was used to determine the SRO. The SRO was defined as the seven frequencies at and below the highest audible frequency in 1/6-octave steps. These frequencies were monitored with fixed-frequency audiometry. At each session, the FLFT test was administered at 80 dB SPL. Subjects used a Békésy-style tracking method to determine the frequency threshold. All testing was completed in a sound booth (single wall, Industrial Acoustics Company) using a computerized, laptop-based, system. FLFT repeatability was calculated as the root mean square difference from the first test session. FLFT accuracy was calculated as the difference from the highest audible frequency determined from fixed-frequency audiometry interpolated to 80 dB SPL level.
RESULTS: The FLFT average RMSD for intersession variability was 0.05 ± 0.05 octaves. The test showed no learning effect [F(3,78) = 0.7; p = 0.6]. The overall intersession variability for SRO fixed-frequency audiometry thresholds at all frequencies was within clinically acceptable test-retest variability (10 dB) at 5.8 dB (range 2.7 to 9.9 dB). The SRO fixed-frequency audiometry therefore served as a repeatable basis of comparison for accuracy of the FLFT test. The mean absolute difference between the fixed-frequency audiometry and FLFT-determined highest audible frequency was 0.03 octaves. The FLFT and the highest audible frequency via fixed-frequency audiometry at 80 dB SPL were not different statistically (p = 0.12). The FLFT took approximately 30 seconds to complete, compared with approximately 4.5 min for fixed-frequency audiometry SRO and 20 to 25 min for a traditional ototoxic audiometric assessment.
CONCLUSIONS: The Békésy-style FLFT was repeatable within 1/12 octave (1 step size in the testing procedure). The FLFT agreed well with the highest audible frequency determined via fixed-frequency audiometry at 80 dB SPL. The FLFT test is amenable to automatic and self-administration and may enable quick, accurate, noise-tolerant ototoxicity, and high-frequency hearing monitoring.