Relationship between neonatal air and bone conduction ABR thresholds

First published: 18 May, 2017
Updated: 20 June, 2018

Introduction

Recently we decided to report raw neonatal ABR results and determine only if they are within the normal range. However this prevents us determining if a hearing loss is conductive or sensorineural.

Solution

Using historical data from neonates we diagnosed with either no hearing loss or a sensorineural hearing loss, we recorded air and bone conduction thresholds for further analysis.

Deming regression

There is an apparent linear relationship between air and the associated bone conduction thresholds. For both AC and BC thresholds there will be:

• Similar measurement error, and
• Similar variance

Deming regression (which assumes error in both x and y measurements) was used to describe the air and bone conduction relationship.

Table 1: Deming regression coefficients

Frequency, Hz	Intercept	SE in Int.	Slope	SE in Slope	Upper lim. Slope
500	-14.694	0.371	0.759	0.008	0.845
1,000	-41.273	2.420	2.879	0.137	4.497
2,000	14.163	0.251	0.642	0.008	0.719
4,000	9.767	0.281	0.691	0.013	0.969

• The standard errors for the 1kHz fit are large suggesting insufficient 1kHz data for a reliable fit.
• For 500 Hz and 2 kHz the upper limit of the 95% confidence interval for the slope is significantly less than 1, meaning that the expected 1:1 relationship between air and bone conduction thresholds is not consistent with the data.

For 500 Hz, 2 kHz and 4 kHz, the regression fits the data quite nicely:

The lower bound at the dotted line is 15dB below the regression line.

Table 2: Estimated bone conduction threshold for a Sensorineural hearing loss

Uncorrected AC threshold	20	25	30	35	40	45	50	55	60	65	70
500 Hz	0	5	10	10	15	20	25	25	30	35	40
2,000 Hz	25	30	35	35	40	45	45	50	55	55
4,000 Hz	25	25	30	35	35	40	45	50

For any sensorineural hearing loss the BC threshold should be not significantly better than the level indicated on Table 2, although in some few cases sensorineural BC thresholds could be up to 15 dB better than the level indicated.