Understanding audiogram patterns is essential for EHS managers who review occupational audiometric surveillance results. This guide covers low-frequency hearing loss: what it looks like on an audiogram, what it means clinically, what OSHA 1910.95 obligations it triggers, and the required employer response. Note that audiogram interpretation in the context of OSHA compliance always requires involvement of a licensed Professional Supervisor — a licensed audiologist, otolaryngologist, or other physician. The EHS manager's role is to understand the pattern well enough to act appropriately and ensure timely PS review.
Soundtrace provides audiometric testing supervised by a licensed audiologist who reviews all audiograms, identifies STSs, and makes clinical determinations — ensuring employer compliance with every 1910.95 audiometric obligation.
What Is Low-Frequency Hearing Loss?
Low-frequency hearing loss appears on an audiogram as elevated thresholds at the lower test frequencies — 500 Hz and 1000 Hz — with better (lower) thresholds at 2000–6000 Hz. This 'reverse slope' or 'ascending' audiogram pattern is the opposite of the typical NIHL high-frequency notch. It is relatively uncommon in occupational settings but occurs in specific exposure scenarios and medical conditions.
Clinical Significance
Low-frequency hearing loss affects vowel sounds and low-pitched environmental sounds. Workers with this pattern may have normal speech understanding in quiet because consonants (which carry most speech intelligibility information) are encoded in the high frequencies, but may report muffled or unclear sound quality, especially for music or bass-heavy sounds. The differential diagnosis includes endolymphatic hydrops (Meniere's disease), low-frequency noise exposure (infrasound, very low-frequency industrial noise), and certain hereditary hearing conditions.
All clinical interpretations of occupational audiograms — including determinations of audiogram pattern, work-relatedness, and STS confirmation — must be made by the Professional Supervisor (licensed audiologist, otolaryngologist, or other physician) under OSHA 1910.95(g)(3). EHS managers should understand these patterns to recognize when PS review is needed and to act on PS findings promptly, not to replace the PS role.
OSHA 1910.95 Implications
Low-frequency hearing loss affects the STS calculation differently than high-frequency NIHL. The STS threshold is calculated at 2000, 3000, and 4000 Hz — if thresholds are elevated at 500–1000 Hz but normal at the STS frequencies, no STS is triggered despite significant hearing loss. However, the 500–1000 Hz elevation is clinically significant and should prompt Professional Supervisor review. If the loss extends into the 2000 Hz range, the STS calculation may be affected. The work-relatedness determination for low-frequency loss requires careful audiological review since the pattern is not typical of NIHL.
Required Employer Response
Low-frequency hearing loss patterns are not typical of occupational NIHL and should always prompt review by the supervising audiologist or physician to rule out medical conditions and assess work-relatedness.
Certain industrial operations generate significant low-frequency noise (below 500 Hz) or infrasound that is not well-characterized by standard OSHA dosimetry. If the worker operates near large HVAC systems, compressors, or industrial fans, low-frequency exposure assessment may be warranted.
Even when the predominant loss is at low frequencies, the OSHA STS calculation is always performed at 2000, 3000, and 4000 Hz. Document both the overall audiogram pattern and the STS calculation clearly in the audiometric record.
Audiologist-supervised audiometric testing with automatic STS detection
Soundtrace audiometric testing is supervised by a licensed audiologist who reviews every audiogram, identifies all STSs, and makes clinical determinations — ensuring your program meets every 1910.95 requirement.
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Low-frequency hearing loss appears on an audiogram as elevated thresholds at the lower test frequencies — 500 Hz and 1000 Hz — with better (lower) thresholds at 2000–6000 Hz. This 'reverse slope' or 'ascending' audiogram pattern is the opposite of the typical NIHL high-frequency notch. It is relatively uncommon in occupational set
Low-frequency hearing loss affects the STS calculation differently than high-frequency NIHL. The STS threshold is calculated at 2000, 3000, and 4000 Hz — if thresholds are elevated at 500–1000 Hz but normal at the STS frequencies, no STS is triggered despite significant hearing loss. How. The Professional Supervisor must review all audiograms with significant findings to determine STS status and work-relatedness.
The Professional Supervisor — a licensed audiologist, otolaryngologist, or other physician — must review any audiogram with clinically significant findings. OSHA 1910.95(g)(3) requires PS involvement in all STS determinations and medical referral decisions. EHS managers should not attempt to interpret audiogram patterns independently.