Predicting the degree of hearing loss using click auditory brainstem response in babies referred from newborn hearing...

The predictive ability of the auditory brainstem response (ABR) is an important factor governing the program sensitivity of neonatal hearing screens. The study examined the accuracy of the click-evoked auditory brainstem response (ck-ABR) when undertaken below the age of 6 months (from expected date of delivery) in predicting the pure-tone thresholds subsequently found to be present in children with a congenital permanent childhood hearing impairment.

Children with permanent childhood hearing impairment were ascertained from neonatal screening programs that have been subject to longitudinal evaluation. Ninety-two children who had ck-ABR recorded when below 6 months of age and repeatable ear specific pure-tone audiometry were recruited. Those with recognized temporary middle ear effusions at either test were excluded. The relationship between ABR and pure-tone thresholds was tested using the Pearson correlation coefficient with a linear regression model used to estimate pure-tone threshold (dependent variable) from ABR (independent variable). Correlation coefficients were obtained for pure-tone frequencies at octave intervals between 0.25 kHz and 4 kHz and at various frequency combinations. The difference between ABR and pure-tone threshold was analyzed. Those with a difference of greater than 20 dB were further examined. The ABR and pure-tone differences were also compared in babies born at term and prematurely.

Of the 92 children recruited to the study two children had a confirmed auditory neuropathy spectrum disorder (2%) and 10 (11%) had an audiometrically confirmed progressive hearing impairment. When these children were excluded, there was a high linear positive correlation (r = 0.90, SE = 14.3 dB) between the ABR and pure-tone thresholds averaged at 2 to 4 kHz. Although the correlation varied for different audiometric configurations, in all cases with a sloping hearing loss the correlation with their best frequency was weaker than the correlation at 2 to 4 kHz. For the total cohort the mean difference between ABR and pure-tone thresholds averaged at 2 to 4 kHz was 4.4 dB (SD = 19.29). The modal difference was 0 dB (58%) and 76 % had a difference of 20 dB or less. ABR underestimated the subsequently recorded pure-tone thresholds by more than 20 dB in 11 children and 10 of these children showed progression of their hearing loss measured by serial pure-tone audiometry. ABR overestimated the pure-tone thresholds by more than 20 dB in 15 children. Nine of these children (60%) had suffered a perinatal illness and the mean difference between the pure-tone and ABR thresholds was significantly greater in those born at <35 weeks of gestation (p < 0.001).

There is a high positive linear correlation between ck-ABR and pure-tone average thresholds at 2 to 4 kHz. However, the predictive value of ABR is reduced in certain neonatal groups. The cause for this is discussed as are the implications for undertaking a test battery at this age to improve the predictive accuracy.