The sense of hearing is important to humans because it facilitates verbal communication. Hearing loss is common and its prevalence increases with age. It can be classified as conductive, sensorineural or mixed. Hearing loss is primarily diagnosed via audiometry that stimulates the cochlea by air and bone conduction. Larger differences between air and bone conduction hearing thresholds are called air-bone gaps and indicate conductive hearing loss. Confirmed air-bone gaps without a conductive hearing loss are known as false air-bone gaps. 

Aim 

This study aims to increase knowledge about normal hearing by investigating the existence of false air-bone gaps with emphasis on thresholds at 4000 Hz and examine its correlation with side, age at the year of the examination, sex assigned at birth and level of sensorineural hearing loss. 

Methods & Results 

Existing audiogram data were collected from 13,417 participants that had undergone audiometry at three hospitals in Östergötland, Sweden, during the years 2018 and 2019. The data were further processed to remove participants with suspected conductive hearing loss and then split into left and right ears per frequency to decrease the number of discarded measurements. The data were processed and analyzed with Excel 365 and SPSS Statistics using non-parametric analyses. 

The four factors were analyzed in regard to air-bone gaps at six different frequencies: 250, 500, 1000, 2000, 3000 and 4000 Hz. Each frequency’s median air-bone gap was statistically significantly different from the others except for 1000 Hz and 3000 Hz. Side differences in air-bone gaps were present at 3000 Hz and 4000 Hz and differences regarding sex assigned at birth were present at all frequencies except for the left side frequencies 500 Hz and 3000 Hz. Age and sensorineural hearing loss were shown to have a moderate to strong correlation where age decreased and sensorineural hearing loss increased the air-bone gap. This study found 5 dB HL air-bone gaps at 250 Hz, 1000 Hz and 3000 Hz and 10 dB HL air-bone gaps at 4000 Hz. 

Conclusions 

The smaller air-bone gaps can be explained by normal variance, but the larger at 4000 Hz suggests that the standard calibration used in audiometry is wrong and needs adjustments. Previous studies have arrived at the same conclusion.