School-Age Hearing Screening Based on Speech-in-Noise Perception Using the Digit Triplet Test
Authors: Denys Sam , Hofmann Michael , Luts Heleen , Guérin Cécile , Keymeulen Ann , Van Hoeck Katelijne , van Wieringen Astrid , Hoppenbrouwers Karel , Wouters Jan 
Published: March 2018

Objectives:
This study aims to investigate the large-scale applicability of the Digit Triplet test (DTT) for school-age hearing screening in fifth grade elementary (5E) (9 to 12 years old) and third grade secondary (3S) (13 to 16 years old) school children. The reliability of the test is investigated as well as whether pass/fail criteria need to be corrected for training and/or age, and whether these criteria have to be refined with respect to referral rates and pure-tone audiometry results.

Design:
Eleven school health service centers participated in the region of Flanders (the Northern part of Belgium). Pure-tone screening tests, which are commonly used for hearing screening in school children, were replaced by the DTT. Initial pass/fail criteria were determined. Children with speech reception thresholds (SRT) of −7.2 dB signal to noise ratio (SNR) (5E) and −8.3 dB SNR (3S) or worse were referred for an audiogram and follow-up. In total, n = 3412 (5E) and n = 3617 (3S) children participated.

Results:
Population SRTs (±2 SD) were −9.8 (±1.8) dB SNR (5E) and −10.5 (±1.6) dB SNR (3S), and do not need correction for training and/or age. Whereas grade-specific pass/fail criteria are more appropriate, a linear regression analysis showed an improvement of 0.2 dB per year of the SRT until late adolescence. SRTs could be estimated with a within-measurement reliability of 0.6 dB. Test duration was also grade-dependent, and was 6 min 50 sec (SD = 61 sec) (5E) and 5 min 45 sec (SD = 49 sec) (3S) on average for both ears. The SRT, test reliability, and test duration were comparable across centers. With initial cut-off values, 2.9% (5E) and 3.5% (3S) of children were referred. Based on audiograms of n = 39 (5E) and n = 59 (3S) children, the diagnostic accuracy of the DTT was assessed. A peripheral hearing loss was detected in 31% (5E) and 53% (3S) of the referred children. Hearing losses found were mild. Less strict pass/fail criteria increased the diagnostic accuracy. Optimal pass/fail criteria were determined at −6.5 dB SNR (5E) and −8.1 dB SNR (3S). With these criteria, referral rates dropped to 1.3% (5E) and 2.4% (3S).

Conclusions:
The DTT has been implemented as the new hearing screening methodology in the Flemish school-age hearing screening program. Based on the results of this study, pass/fail criteria were determined and optimized to be used for systematic hearing screening of 5E and 3S school children. Furthermore, this study provides reference values for the DTT in children 9 to 16 years of age. Reliable SRTs can be obtained with the test, allowing accurate monitoring of hearing over time. This is important in the context of a screening guideline, which aims to identify children with noise-induced hearing loss. Validation of the screening result should go beyond taking an audiogram, as a peripheral hearing impairment cannot always be found in children with a failed test.