Computing an STS on a Possibly Invalid Annual Audiogram
At a concrete products plant, an employee's baseline audiogram was recorded at age 44 and the annual audiogram at age 45. Baseline right ear: 10 dB at 500 Hz, 10 at 1000, 15 at 2000, 20 at 3000, 30 at 4000, 25 at 8000. Annual right ear: 15, 15, 25, 35, 45, 40. Left ear baseline: 5, 10, 10, 15, 20, 20; annual left: 10, 10, 15, 20, 25, 25. The annual test was performed in a converted conference room three hours into the shift, with no quiet period beforehand; the room's background noise at 2000 Hz was measured at 50 dB. The tester noted that the employee had a cold and "did not seem to understand the instructions."
1. Calculate whether a standard threshold shift has occurred, showing the arithmetic for each ear.
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Definition. An STS is an average shift of 10 dB or more at 2000, 3000 and 4000 Hz in either ear, relative to baseline.
Right ear:
- Baseline average = (15 + 20 + 30) / 3 = 21.7 dB
- Annual average = (25 + 35 + 45) / 3 = 35.0 dB
- Shift = 13.3 dB → standard threshold shift
Left ear:
- Baseline average = (10 + 15 + 20) / 3 = 15.0 dB
- Annual average = (15 + 20 + 25) / 3 = 20.0 dB
- Shift = 5.0 dB → not an STS
Judgment points. Only 2000, 3000 and 4000 Hz count; the 500/1000 Hz changes and the 8000 Hz change are irrelevant to the calculation. Age correction is optional and over a one-year interval would not erase a 13 dB shift. The right ear alone is enough to make this an STS, so the case proceeds to follow-up - but see the validity problem before acting on it.
2. Are there reasons to doubt this annual audiogram, and what should be done before it is treated as final?
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Three validity problems:
- No 14-hour quiet period. Testing three hours into the shift likely captures a temporary threshold shift and exaggerates the loss.
- Background noise of 50 dB at 2000 Hz exceeds the maximum permissible test-room level for that octave band (47 dB at 2000 Hz), so tones may be masked by room noise and thresholds elevated.
- A head cold and apparent failure to understand instructions cast doubt on response reliability.
What to do. Do not accept the result as final. Retest within 30 days, after at least 14 hours without workplace noise (protectors worn so exposure stays at or below 85 dBA can satisfy this), in a room meeting the octave-band limits or with insert earphones plus a background survey. Perform otoscopy, reinstruct the employee, and confirm the calibration status of the audiometer.
Outcome logic. If the retest no longer shows an STS, the retest may be treated as the annual audiogram and the reasoning documented. If it does, the STS stands and follow-up proceeds.
3. If the retest confirms the shift, what follow-up is required, and can the baseline be replaced with this annual audiogram?
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Required follow-up.
- Notify the employee in writing within 21 days of the determination.
- Fit or refit hearing protectors, retrain, and require their use; re-evaluate attenuation against actual exposure.
- Refer for clinical audiological or otologic evaluation where the professional suspects medical pathology or the shift persists.
- Retain the audiogram with examiner, date, and calibration information.
- Consider whether engineering controls are needed rather than relying on protectors alone.
Baseline revision. A baseline may be replaced by the annual audiogram when hearing has improved - this prevents a low outlier baseline from generating false shifts forever. Here hearing is worse, so the baseline must stay; replacing it would erase the trend and hide progression.
Judgment point. The purpose of the baseline is comparison over time. A revision that makes an STS disappear is defensible only when the original baseline was artificially low, and the record must show why.