The significance of masking for the poor hearing ear in pure tone audiometry

In pure tone audiometry, when the difference of the Average Air Conduction Threshold of pure tone (AACT) between bilateral ears is more than 40 dB HL masking must be performed on the poor side, However, we found that masking also make significance difference when the binaural AACT difference (AACT-d)was less than 40 dB HL in some patients.

Assessing the significance of masking for the poor ear in pure tone audiometry in patients with different types of deafness to obtain preoperative accurate hearing.

A comparative analysis of 163 cases (163 ears) with hearing difference between two ears was conducted, who were divided into three groups: G1 Congenital Malformation of the Middle and Outer Ear (CMMOE)as conductive deafness, 63 ears, G2 sudden deafness as sensorineural deafness, 65 ears, and G3 media otitis as conductive or mixed deafness,35 ears. AACT-d before and after the poor ear masking was analyzed under the following three conditions: (1) 0.125-8 KHz each frequency, (2) 0.5-4 KHz on average, (3) the frequencies of AACT-d ≥ 40 dB HL and <40 dB HL between the two ears before masking. If the sample data did not follow a normal distribution, the Wilcoxon rank sum test was used for comparasion of AACT, and p < 0.05 was considered statistically significant. It is clinically effective for AACT-d ≥ 15 dB HL at 1 frequency or 10 dB HL ≤ AACT-d at 2 frequencies <15 dB HL before and after masking.

Among the three groups, (1) the comparasion of AACT-d before and after the poor ear masking for each frequency of 0.125-8 KHz and 0.5-4 KHz on average with all p < 0.05, and the AACT-d of the G1 group was the largest, with an average 0.5-4KHz of 7.5 dB HL, and the first two were 14.5 dB HL and 13.8 dB HL at 0.125 KHz and 0.25 KHz, respectively. (2) AACT-d ≥ 40 dB HL and <40 dB HL between the two ears before masking were distributed at the full frequency of 0.125-8KHz, the clinically effective rates of ≥40 dB HL groups were G1 (89.3%), G2 (45.5%) and G3 (5.3%), while those of < 40 dB HL groups were G1 (69.7%), G2 (34.4%) and G3 (31.3%), respectively.

For all three groups, there was statistically significant in AACT-d before and after the poor ear masking across each frequency of 0.125-8 KHz and on average 0.5-4 KHz. The distribution of AACT-d ≥ 40 dB HL and <40 dB HL between the two ears before masking was observed throughout the full frequency range of 0.125-8 KHz. AACT-d before and after the poor ear masking showed clinical effectiveness in all three groups, with the highest effective rate observed in the G1 group and the highest AACT-d at 0.125 KHz and 0.25 KHz. Therefore, regardless of whether the AACT-d between the two ears before masking is ≥40 dB HL or <40 dB HL, the full frequency masking should be employed in three groups, especially for the G1 group of CMMOE, particularly at 0.125 KHz and 0.25 KHz.