Characteristics of the audiometric notch as a clinical sign of noise exposure

This study investigated variability in audiometric notch recognition by asking three clinicians to identify notches in the audiograms of 634 noise-exposed employees. Agreement between the raters was assessed, and three notch characteristics, frequency, depth and shape (a wide or narrow notch), were investigated as recognition factors. The proportions of positive tests reported by each rater were 0.26, 0.49 and 0.68, respectively. The 'all rater' index of agreement was 0.45, and the range for pairwise comparisons was 0.14 to 0.52. With recognition factors, rater 1 was most strongly influenced by depth, rater 2 by shape and rater 3 by a possible combination of criteria. To reduce variability we suggest that narrow notches should be at least 15 dB in depth, and that broad notches should have a depth of 20 dB, with a recovery of at least 10 dB at the high end. Care should also be taken to elicit a sufficient history of noise exposure, and ensure that there are no other explanations for the notch.