Baseline Audiogram Best Practices: Getting It Right from the Start

Every hearing conservation program rests on a foundation: the baseline audiogram. This initial hearing test becomes the reference point against which all future audiograms are compared. If the baseline is flawed, every subsequent Standard Threshold Shift (STS) determination built on it will be unreliable.

Despite its importance, baseline audiogram quality is one of the most overlooked aspects of hearing conservation programs. Here's how to get it right.

What Is a Baseline Audiogram?

The baseline audiogram is the first valid audiogram obtained for an employee after entering a hearing conservation program. It establishes the employee's hearing thresholds at standard audiometric frequencies (500, 1000, 2000, 3000, 4000, 6000, and 8000 Hz) for both ears.

All future annual audiograms are compared against this baseline to detect changes in hearing — specifically, the Standard Threshold Shift (STS) at 2000, 3000, and 4000 Hz.

OSHA Timing Requirements

OSHA requires the baseline audiogram to be obtained:

• Within 6 months of an employee's first exposure to noise at or above the action level (85 dB TWA)
• Within 12 months if a mobile testing service is used — but the employee must wear hearing protectors during the extended period

Missing the baseline window is one of the most common OSHA citations in hearing conservation. Track new hires from day one and schedule their baseline before the deadline.

Ensuring Baseline Validity

Quiet period before testing

The single most important factor in baseline quality is avoiding noise exposure before the test. OSHA requires at least 14 hours of quiet (no occupational noise exposure) before the baseline audiogram. This means:

• Testing should be done at the start of a work shift, before noise exposure begins
• If testing mid-shift, the employee must have worn hearing protection for the preceding 14+ hours
• Weekend or pre-shift testing is ideal

Noise exposure before baseline testing can temporarily elevate thresholds (temporary threshold shift, or TTS), making the baseline appear worse than the employee's true hearing. This inflated baseline then masks real hearing loss on future comparisons.

Proper audiometer calibration

Ensure your audiometer has current calibration — both daily biological checks (a person with known stable hearing listens and verifies) and annual acoustic calibration by a qualified technician. Record calibration dates, as OSHA requires this information on every audiometric record.

Testing environment

Background noise in the testing room can elevate thresholds, particularly at low frequencies. Test booths should meet the maximum permissible ambient noise levels specified in OSHA's Appendix D. If ambient noise is too high, the baseline will be falsely elevated.

Tester technique

The person administering the test must be trained and certified (CAOHC certification for technicians). Consistent instruction to the subject, proper headphone placement, and adherence to the modified Hughson-Westlake procedure all affect test quality.

When to Revise the Baseline

The baseline isn't necessarily permanent. OSHA allows — and in some cases recommends — baseline revision when:

• Persistent STS: If an STS is confirmed on retest and appears to represent a permanent change in hearing, the reviewing professional may recommend revising the baseline to the new stable level
• Improved hearing: If an employee's hearing improves significantly relative to the baseline (which can happen if the original baseline was obtained during a temporary threshold shift), the baseline should be revised downward

Should you revise?

This is a judgment call for the reviewing audiologist or physician. Consider:

• Revise if the STS has been confirmed on retest and is present in consecutive annual audiograms. This prevents the same STS from being flagged year after year
• Don't revise if the change may be temporary, or if the employer wants to maintain the original baseline to track cumulative hearing loss from the start of employment

Some organizations maintain a "dual baseline" approach — keeping the original baseline for long-term trend analysis while using a revised baseline for annual STS determination. AudiVault supports both approaches, automatically comparing against the appropriate baseline based on your organization's policy.

Baseline for Different Test Types

Pre-employment / pre-placement audiograms

Many employers obtain audiograms during the hiring process. These can serve as the OSHA baseline if they meet the 14-hour quiet period requirement and are performed with calibrated equipment by qualified personnel.

Mobile testing services

When using a mobile van, the extended 12-month window applies, but hearing protector use during the interim period must be documented. The mobile testing environment must still meet background noise standards.

Exit audiograms

While not required by OSHA, exit audiograms are valuable for establishing an employee's hearing status at separation. They don't replace the baseline but provide a useful endpoint for the employee's hearing history.

Technology and Baseline Management

Software plays a critical role in baseline management:

• Automatic baseline tracking: The system should identify which audiogram is the current baseline for each employee and use it for all STS calculations
• Revision history: When a baseline is revised, both the original and revised baselines should be retained in the record
• Alert for missing baselines: New employees approaching the 6-month deadline should be flagged
• Trend visualization: Audiogram comparison charts that show changes relative to baseline over time