Pure Tone Audiometry

If you suspect a loss, the first thing your doctor shall advice you is to undergo Hearing Tests. These can be screening tests as well as diagnostic tests. Let us understand what these tests are:

- If you need to get hearing test for individuals above 8 years of age having normal development and IQ, then you would be advised PTA (Pure tone audiometry)

- If you wish to assess the hearing in Infants, new born or in children below the age of 8 years, then you would be advised to go for BERA (Brainstem Evoked Response Audiometry), ASSR (Auditory Steady State Response), OAE (Auto Acoustic Emissions)

Let us understand what these tests are and how to interpret their results: In this segment we shall take up the PTA test and understand its interpretations.

1. Pure Tone Audiometry

PTA or pure tone audiometry is a hearing test accepted worldwide as a standard protocol for determining hearing levels or hearing loss.

Prerequisites for this test:
-> The individual undergoing this test should be 8 years and above.
-> PTA should be done in an acoustically treated room with least noise interference. If not then the audiologist or the hearing professional should determine a correction factor which shall be applied to the overall outcome.
-> The audiometer machine should be calibrated before the test is done.
-> Hearing screening is sometimes done using in-situ audiometry with hearing aids. This however should not be taken as a benchmark for true hearing threshold estimation.

Procedure:

A TDH 39/TDH 49 headphone connected to the audiometer is placed to the individual while he is seated in an acoustic chamber. The audiologist presents sounds i.e. Puretones to the individual, and marks the least audible sounds the individual responds to for each frequency. These thresholds obtained via headphones are known as ‘Air Conduction’ thresholds. Once this is done, the audiologist performs a bone conduction test in which a small vibrator is put on the mastoid region and similar pure tones are presented and thresholds obtained. These thresholds are called bone conduction thresholds. An audiologist may use different procedures for obtaining true thresholds of each individual ear.

Inference

This test helps us determine the hearing power of the individual. Basis this test we can also diagnose which part of the ear i.e. the outer, middle or inner ear is at fault and which type of hearing loss i.e. whether it is a conductive hearing loss, sensorineural hearing loss or mixed hearing loss; an individual is suffering from. Here conductive pertains to loss in outer or middle part of the ear, sensorineural pertains to loss in the inner ear and mixed pertains to loss that can be in outer or middle as well as the inner ear.

Interpreting the Audiometry Test Graph

The Audiometry test graph is basically represented on X-Y axis. The X axis represents the frequencies on which the pure tones are presented and Y axis represents the loudness of the sounds in decibels.
The Air conduction thresholds for the right ear are represented by a “O” mark or a “∆”; whereas the Air conduction thresholds of the left ear are represented by a “X” symbol or “□” symbol.

The bone conduction thresholds are represented for the right ear by ‘<’ symbol and ‘[‘ symbol; and for the left ear ‘>’ and ‘]”. In general the denotation of hearing thresholds of right ear is represented by red colour and for left ear by blue.

The interpretation of audiometry test is quite elaborate however for a layman it can be understood in two ways i.e. severity of hearing loss and type of hearing loss.

Severity of hearing loss: There are 4 stages of hearing loss, mild, moderate, severe and profound; thereafter it becomes a deaf ear. Hearing loss can be different on all frequencies and can fall under any severity. You can check which category your hearing loss falls under looking at the picture below:

Hearing Test

Audiometry Graph

The average of your audiogram is determined by calculating an average of the Air conduction thresholds obtained at 500Hz, 1000Hz and 2000Hz. Following are the hearing loss degrees:

* If this average falles between 0dB to 25dB then your hearing is normal
* If this average falls in between 25dB to 40dB then you have a mild hearing loss
* Between 41dB to 55dB you have moderate loss
* Between 56dB to 70dB you have moderately severe loss
* Between 71dB to 90dB you have severe loss
* Above 90db you have profound hearing loss

Type of hearing Loss: The type of hearing loss can be understood by noting the difference between Air conduction and Bone conduction thresholds of each ear.

-> If the BC thresholds falls in the normal zone and AC threshold in the loss zone then it becomes conductive hearing loss in that particular ear.
-> If both BC and AC thresholds fall in loss zone and difference between BC and AC is more than 10dB then it is a mixed hearing loss in that ear
-> If Both BC and AC thresholds fall in the loss zone and difference Between BC and AC thresholds is less than 10dB, then it’s a Sensorineural hearing loss in that ear

If you seek advice on PTA testing, you can write to us through the form below. We provide audiology services in Pune, Mumbai, Hyderabad, Bangalore and Delhi NCR.

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