Pure-Tone Air-Conduction and Bone-Conduction Threshold Audiometry with and without Masking in Adults and Older Children (ECPG)
"last update: 26 August 2024"
- Executive Summary
1. Equipment and test environment
• Audiometer, transducers and response buttons SHALL be clean and calibrated. (Strong Recommendation)
• Ambient noise SHOULD NOT exceed the levels permitted (35dB (A)) measured by the sound level meter. (Conditional Recommendation)
• Infection control measures SHOULD be applied. (Conditional Recommendation).
2. Preparation of the test (Strong Recommendation)
• Otoscopic examination: Findings recorded, including the presence of wax and ear canal collapse. Occluding wax SHALL be removed prior to audiometry and use insert earphone in case of ear canal collapse.
• Subject SHALL be asked about any exposure to loud noise during the previous 24h. If the answer is yes, then more details SHOULD be obtained regarding the exposure and results recorded. Temporal threshold shift should be taken into consideration. It may be necessary to re-test the subject at a time when they have had no recent exposure to noise.
• Subjects SHALL be asked if they have tinnitus, if yes, start with ear without tinnitus and a frequency modulated or warble tone may be used as a stimulus. It is essential to record at which frequencies and in which ears warble tones were used. The use of pulsed tones and narrow-band noise is not advised due to calibration and perception problems.
• Subjects SHALL be asked if they have better hearing in one ear, if so, testing SHOULD commence with that ear.
3. Threshold Estimation (Air/Bone conduction audiometry)
• Instructions: Remove any hearing aids, also any glasses, headwear or earrings that may obstruct the correct placement of the transducers, cause discomfort or affect sound transmission. Wherever possible, hair, scarves etc, SHOULD NOT be allowed to sit between the ear and the transducer. (Conditional Recommendation)
• Subject’s response: SHOULD be clear. (Conditional Recommendation)
Earphones:
There are three main types of transducers that can be used for air-conduction audiometry: supra-aural, circum-aural and insert earphones. (Strong Recommendation)
➡️Test order (Conditional Recommendation)
Start with the better-hearing ear (according to the subject’s account) and at 1000 Hz. Next, test
2000 Hz, 4000 Hz, 8000 Hz, 500 Hz and 250 Hz in that order. Then, for the first ear only, retest at 1000 Hz.
➡️Timing of the test stimuli (Conditional Recommendation)
The duration of the presented tone SHALL be varied between 1 and 3 seconds. The interval between the tones SHALL be varied between 1 second and at least 3 seconds.
➡️Initial familiarization (Conditional Recommendation)
Present a tone of 1000 Hz that is clearly audible (e.g. at 40 dB HL for a normally hearing subject or approximately 30 dB above the estimated threshold for a subject with a hearing impairment, but never more than 80 dB HL). If there is no response, increase in 10-dB steps until a response occurs. If the tone is still inaudible at 80 dB HL, increase 5-dB steps until a response occurs, taking care to monitor the subject for discomfort.
➡️Method for finding threshold. (Conditional Recommendation)
Threshold is defined as the lowest level at which responses occur in at least half of a series of ascending trials with a minimum of two responses required at that level. Apply the method of (Down 10dB up 5dB till 50% response)
+/- masking. Start with 1 KHz. Proceed to the next frequency, starting at a clearly audible level (e.g. 30 dB above the adjacent threshold) in the frequency range 250-8000Hz.
Variations in technique SHALL be recorded (Strong Recommendation)
➡️Bone conduction audiometry
Placed over the mastoid prominence of the worse hearing ear (Strong Recommendation)
Performed in the frequency range 500 Hz to 4000. Tested ear should be occluded with ear plug when testing 4000 Hz b-c. The procedure is similar to the AC audiometry. (Conditional Recommendation)
4. Masking (Conditional Recommendation)
Cross-hearing and masking
• Rule 1
Masking is needed at any frequency where the difference between the left and right not-masked a-c thresholds is 40 dB or more when using supra- or circum-aural earphones or 55 dB when using insert earphones.
• Rule 2
Masking is needed at any frequency where the not- masked b-c threshold is better than the air-conduction threshold of either ear by 10 dB or more.
• Rule 3
• Masking will be needed where the b-c threshold of one ear is more by 40 dB (if supra or circum-aural earphones have been used) or 55 dB or more (if insert earphones have been used) than the not- masked a-c threshold attributed to the other ear.
• Instructions for masking
Procedure for masking (plateau-seeking method for masking)
▪️ Re-establish hearing threshold in the test ear by presenting the tone and seeking the response without masking noise to remind the subject what to listen for.
▪️ Introduce masking noise to the non-test ear. The initial level of masking should be the effective masking level which is equal to the tonal threshold level of that ear at that frequency.
▪️ Using increments of 10 dB in masking noise, until you have at least four measurements (including the initial starting point) and until three successive measurements yield the same tonal threshold. You may be unable to obtain this plateau due to maximum level of the audiometer being reached or because the subject finds the masking noise uncomfortable.
5. Audiometric Description Recommended format and symbols (Conditional Recommendation)
• Five descriptor average hearing thresholds levels (dB HL) according to (ASHA, 2015). These are based on the average of pure tone hearing threshold at frequencies (250Hz, 500 Hz, 1KHz,2 KHz and 4KHz).
|
Mild |
26-40 (Adults)/ 16-40 (Children) |
|
Moderate |
41-55 |
|
Moderately Severe |
56-70 |
|
Severe |
71-90 |
|
Profound |
More than 91 |
Report SHOULD illustrate (Type, Degree and configuration) of the hearing loss. There are three basic types of hearing loss: conductive, sensorineural hearing loss (SNHL), and mixed (ASHA, 2005). The configuration, or shape, of the hearing loss refers to the degree and pattern of hearing loss across frequencies. For example, a hearing loss that only affects the high tones would be described as a high-frequency loss.
• Recommended format and symbols as the following table (ASHA, 1990).
• Air-conduction symbols SHOULD be connected with continuous straight lines; bone-conduction symbols SHOULD be joined with broken lines.
