Explain the procedures for conducting baseline and annual audiometric testing, and identify the criteria used to classify significant threshold shift.
Audiometric testing is a critical component of a hearing conservation program (HCP) aimed at detecting and preventing noise-induced hearing loss (NIHL). It involves measuring an individual's hearing thresholds at various frequencies to establish a baseline of hearing and track changes over time. Baseline and annual audiograms follow specific procedures, and the results are analyzed using defined criteria to identify a significant threshold shift.
Baseline Audiometric Testing:
Baseline audiometric testing is the first hearing test conducted on an employee who is or will be exposed to noise at or above the action level. The main goals of baseline testing are to establish a reference point of an employee’s hearing and to identify any pre-existing hearing issues. It is essential that this testing is carried out correctly, using the correct methods.
1. Test Environment: The test should be conducted in a quiet room or sound-treated booth that meets specific acoustic standards. The room needs to have minimal background noise and be sufficiently insulated so that external noise is not audible to the test subject. The background noise must be measured to ensure compliance with ANSI or other relevant standards for audiometric testing.
2. Equipment Calibration: The audiometer used for the test must be calibrated at regular intervals according to the manufacturer's instructions. Calibration ensures that the equipment is measuring sound levels accurately. The calibration should be checked prior to the start of testing.
3. Patient Preparation: The patient should be given clear instructions about the test procedure, and their full cooperation should be sought. They should also be asked if they have had any significant noise exposure, a head cold, or any other factors that may influence the test. The patient should be shown how to indicate when they hear a sound. It is usually carried out by the raising of a hand or pressing a button.
4. Otoscopic Examination: Prior to the hearing test an otoscopic examination is performed to inspect the external ear canal for any obstructions, such as ear wax, inflammation, or any other condition that might interfere with the test result. Any conditions found should be noted in the patient record, and if necessary a hearing test can be rebooked for a later date.
5. Pure-Tone Threshold Testing: The pure-tone test is used to establish hearing thresholds. The audiometer generates pure tones at specific frequencies (typically 500, 1000, 2000, 3000, 4000, and 6000 Hz). The test typically starts at 1000 Hz, and the tone is presented at varying intensity levels, with higher and lower intensities tested in a series of steps. The patient is required to signal when they can hear the tone. The threshold at each frequency is determined as the lowest sound intensity that can be heard consistently. The procedure is repeated for each test frequency and for both ears separately.
6. Recording Results: The thresholds for each frequency in each ear are recorded on an audiogram. This audiogram is a graph showing the hearing thresholds at different frequencies, and is used to assess the patient’s hearing. The audiogram becomes the baseline for comparison in subsequent annual tests.
Annual Audiometric Testing:
Annual audiometric testing is conducted on employees exposed to noise at or above the action level to monitor for any changes in their hearing thresholds over time.
1. Same Test Environment and Equipment: The annual test is carried out in the same environment as the baseline test and using the same equipment. This consistency ensures that the results from each test are comparable.
2. Patient Preparation: The same patient preparation steps are followed as for the baseline test, including a pre-test otoscopic examination to assess the external ear canal. The patient should also be asked if they have been exposed to significant noise, or have any other condition which may influence the outcome of the test.
3. Pure-Tone Threshold Testing: The same procedure as for the baseline test is used, with the same test frequencies and intensities presented, and the same patient response methods used.
4. Comparison with Baseline Audiogram: The results of the annual test are compared directly to the baseline audiogram. This comparison is essential to identify any significant threshold shift.
5. Recording Results: The audiogram is recorded for the patient’s records, and any threshold shifts must be noted and reported.
Criteria for Significant Threshold Shift (STS):
A significant threshold shift is an indication that a person's hearing has deteriorated and requires further investigation and preventative action. The criteria for defining a STS vary slightly among different regulatory bodies, but are typically based on changes in average hearing thresholds at certain frequencies. OSHA defines STS as an average change in hearing threshold of 10 dB or more at 2000, 3000, and 4000 Hz in either ear.
Here are common criteria for identifying STS:
1. OSHA criteria: A 10 dB average threshold shift at 2000, 3000, and 4000 Hz in either ear, when compared to the baseline audiogram.
2. Other Considerations: There may also be consideration of changes in thresholds at other frequencies. For example, a shift of 15 dB or more at any single frequency, or specific changes in low frequencies may require further investigation and action.
3. Age Correction: Some audiometry protocols include adjustments to the hearing thresholds based on age, because hearing acuity is known to decline over time, irrespective of workplace noise exposure.
4. Confirmation Audiogram: If a STS is identified in the annual test, a confirmation audiogram is usually performed. This is to verify the initial finding and is often carried out within a few weeks of the initial test. This confirmation step minimizes the influence of any temporary changes that may be present. If the STS is confirmed, the person is designated as having a STS.
5. Follow Up Procedures: If a STS is confirmed, specific steps should be taken, including review of HPD use, training, and a re-evaluation of noise control strategies. The worker may require referral to an audiology professional for further investigation.
Identifying an STS is crucial to initiate further actions within the hearing conservation program. This might include additional training, re-evaluation of HPD selection, or changes to workplace noise controls, with an aim of preventing further NIHL. The audiogram data collected through baseline and annual testing provides valuable insights into the effectiveness of the entire hearing conservation program and guides any necessary improvements.