Regulations and standards that cover the use of audiometers exist globally. While some differ, most, if not all, require that the equipment is calibrated and maintained regularly and records are kept for auditing.
The Occupational Safety and Health (OSHA), the South African National Standard (SANS), the American National Standards Institute (ANSI) and the International Organization for Standardization (ISO) insist on having equipment calibrated and checked on a routine basis.
Therefore, everyone must calibrate audiometers to ensure that they comply with their country/state’s regulations and ensure testing accuracy.
While amongst most clinicians, the need for regular audiometry calibration is understood, some have viewed regular calibration as an unnecessary and avoidable task.
I wrote an article a while back on why the calibration of your audiometer is the key to accurate results. This article focused on what calibration is, and why it is important in ensuring that you yield accurate and reliable audiometric measures.
An uncalibrated audiometer will lead to inaccurate test results.
But why do audiometers go out of calibration?
The audiometer itself does not go out of calibration often, the components that accompany it, however, may have an effect on the accuracy of results, which is the reason that they should be calibrated together. The age of the audiometer, wear and tear, prolonged exposure to moisture, and rough handling can affect calibration as well as cause damage to components.
In essence, regular calibration and maintenance help to uncover issues so that they can be rectified.
It is important to note that the user of the audiometer is responsible for inspection of cables, transducers, and interface cables on a regular basis, rather than relying on annual servicing alone. Any signs of damage or wear and tear should be communicated to the manufacturer or service provider for rectification.
What's the risk of not calibrating your audiometer?
Audiometers assess and diagnose hearing sensitivity. Treatment plans are based on the results of the hearing test. The accuracy of hearing tests is a vital factor in patient outcomes.
In audiology, test results determine the treatment plan. Inaccurate results can result in a missed diagnosis, unnecessary treatment, and could possibly lead to further damage.
In industrial audiology, hearing thresholds are used to make decisions on the compensation of disability due to hearing loss. They may also be used to investigate whether or not the patient is at fault due to neglecting to use the provided safety equipment. On one hand the company loses the other the patient loses, but there is no winner when it comes to inaccurate results.
In hearing screening, an uncalibrated audiometer can either produce false referrals or under referrals. The former places an unnecessary burden on the referral system and inflates costs while the later puts patients at risk of missing out on treatment opportunities early on.
In cases where patients are unnecessarily referred, the cost of further testing then transferred to the patient unnecessarily.
Calibration intervals according to regulations.
Standards are developed to ensure that manufacturers of audiometric equipment and users of the equipment are all on the same page - in all countries. The specific parameters that must be checked in an audiometer and the various instruments required to electro-acoustically calibrate the audiometer are outlined in standards provided by the likes of ANSI, IEC and ISO.
It is beyond the scope of this article to discuss electroacoustic calibration in detail. Instead, I will outline what is required according to the various standards,
SANS (South African National Standards)
Audiologists in audiology practice:
- The audiometer is to be calibrated annually.
Audiologists in occupational health:
- If the device is used for occupational health, the audiometer is to be calibrated annually if situated in a static clinic and is not moved.
- If the audiometer is moved from its original point of calibration ie. part of a mobile booth setup or is portable and is moved from office to office, the audiometer is to be calibrated every three months.
- Note that this is also a requirement of the British Society of Audiology for all audiometers when used in industrial audiometry.
ANSI and OSHA:
- Audiometer calibration is to be electro-acoustically checked annually
- When used in industrial audiometry, calibrate quarterly
Please check with your local authorities on the intervals of calibration in your country
Biological calibration check - routine checks
Initial electro-acoustic calibration (EAC) is conducted by the manufacturer before dispatching the device or upon installation and on a regular basis going forward. This calibration guarantees that, at the date of issue, installation or calibration, the equipment is functioning correctly and accurately.
This does not cover the device over time.
It is the clinician's responsibility to ensure the performance and functionality of the device on a daily basis before testing begins.
That is where biological calibration checks come in.
They are used to test and verify the functionality and accuracy of the device prior to testing or if the clinician suspects the equipment is not performing as expected.
A daily check could indicate that the device, while seemingly operational, is in fact, no longer accurate. In which case, testing must be halted and the audiometer should be sent in for calibration even if it is before it’s scheduled calibration interval.
The biological check consists of two components:
- Device listening checks
- Hearing threshold checks.
Device listening checks
The device listening checks involve listening to any unusual sounds, such as hum, static or cracking noise. This should be checked with the device on but not presenting tones and when the device is presenting tones. Any undesired sounds/s should prompt further investigation by a calibration technician.
Hearing threshold checks.
The hearing threshold checks should be conducted on an individual whose hearing status is known and stable. Both ears are tested, the transducers are then swapped around and the test repeated. Note that you are using the same ear to test both transducers, so the results should be similar. The results should be within ± 5 dB of each other. If so, the device can be assumed to be within calibration. If results differ more than ± 5 dB, the audiometer may need to be EAC.
X-check… Objective verification replaces biological checks
There is an easier and quicker way of assessing your device’s calibration annually. This is X-check (cross-check), this is a digital calibration verification tool built into the KUDUwave device and comes standard with every KUDUwave audiometer. It allows for accurate (within 5 dB) calibration checks to ensure that your audiometer yields valid results. This turns a traditionally “subjective” test which can be affected by the subject’s health into an objective and highly accurate test. Using X-check is really easy and will save you a lot of time.
As mentioned above, EAC should be undertaken annually (or as per your country’s standards) or more frequently if circumstances dictate as it is paramount to valid, accurate and reliable results.