Degrees of hearing loss versus Grades of hearing impairment and some maths on how to classify the configuration of hearing loss

While hearing loss is defined as partial or total inability to hear sounds with one or both ears, it is much more complex than that. To that end, a lot of research has been done and an important number of standards have been written regarding the topic of hearing loss. This vast amount of information has served to better classify hearing loss, to reduce the complexity of its definition and to assist clinicians in uniform diagnosis of hearing loss. 

You have just performed an audiometry test, and you have a patient’s audiogram in front of you - now what? This article is an extension of a previous blogpost we wrote titled: How to read an audiogram. Our aim is to shed some light on seemingly confusing details such as the degree vs grades of hearing loss and their configurations. 

Degree of Hearing Loss vs Grades of Hearing Impairment

There is sometimes a great deal of confusion among clinicians when differentiating between the Degree of Hearing Loss and the Grade of Impairment. ASHA has assisted clinicians by defining the Degree of Hearing loss as the severity of the hearing loss. This is based on “how loud sounds need to be” in order for the patient to hear them. Below is a table that shows common ways of classifying hearing loss according to its severity. It is important to note that some clinicians base the severity of hearing loss on thresholds at individual frequencies. However, some clinicians base the degree of hearing loss on the pure tone average of 500, 1000 and 2000 Hz of air conduction thresholds. 

ASHA - Degree of hearing loss

Degree of hearing loss

Hearing loss range (dB HL)

Normal

-10 - 15

Slight

16 - 25

Mild

26 - 40

Moderate

41 - 55

Moderately severe

56 - 70

Severe

71 - 90

Profound

91+ 

Source: Clark, J. G. (1981). Uses and abuses of hearing loss classification. Asha, 23, 493–500.

 

Let’s move on to the Grades of Hearing Impairment. According to the World Health Organisation (WHO), the Grades of Hearing Impairment are relevant for the purpose of remediation (recommendation of care) after an individual’s acquisition of hearing loss. The following table further indicates what hearing performance you could expect from an individual with a certain Grade of Impairment (Hearing loss). 

WHO - Grade of Hearing Impairment

Grade of hearing impairment

Corresponding audiometric ISO value

Performance

Recommendation

0 - No impairment

25 dB or better (better ear)

No or very slight

hearing problems. Able to hear whispers.

 

1 - Slight impairment

26-40 dB

(better ear)

Able to hear and repeat words spoken in normal voice at 1 metre.

Counselling. Hearing aids may be

needed.

2 - Moderate impairment

41-60 dB

(better ear)

Able to hear and repeat words spoken in raised voice at 1 metre.

Hearing aids usually recommended.

3 - Severe impairment

61-80 dB

(better ear)

Able to hear some

words when shouted

into better ear.

Hearing aids needed. If no hearing aids

available, lip-reading and signing

should be taught.

4 - Profound impairment including deafness

81 dB or greater (better ear)

Unable to hear and understand even a shouted voice.

Hearing aids may help understanding

words. Additional rehabilitation needed.

Lip-reading and sometimes signing

essential.

Source: World Health Organisation Grades of hearing impairment (WHO, 2008)

*The audiometric ISO values are averages of values at 500, 1000, 2000, 4000 Hz.

Close inspection of the WHO table for Grade of impairment suggests that there is slight lenience when defining ‘’no hearing loss/no impairment’’. The use of these two tables is important, with each one having  different clinical reasons. In my anecdotal evidence, most audiologists that I have worked with, or that I know, tend to use the ASHA 'degree of hearing loss’ to classify the severity of loss on the audiogram. Most of these clinicians are experienced and very knowledgeable in audiology. Nonetheless, the WHO Grade of Impairment is a good source in these two cases: 1. you are a start-up clinician or, 2. you would like to have validated information on what to expect with a certain loss and what to do about it from a clinical standpoint. 

Differences between the Degree of Hearing Loss and the Grade of Hearing Impairment

 

Degree of hearing loss

Grade of hearing impairment

Who published this classification?

ASHA

WHO

Reason for classification?

To determine the severity of hearing loss in each ear

To determine the grade of hearing impairment, hearing performance and management recommendations of the hearing loss (in the better ear)

How many degrees/grades are there?

7

5

What is the highest threshold that still indicates normal hearing

15dB

25dB

Are there different ranges for the degrees/grades for children and adults

No

No, but hearing disability in children starts at 31 dB and for adults at 41 dB

Does this classification look at each ear individually

Yes

No, the hearing thresholds of the best ear is used

What frequencies are averaged?

500Hz, 1000Hz and 2000Hz

500Hz, 1000Hz, 2000Hz anf 4000Hz

When is hearing loss classified as Profound?

>80dB

>91dB

 

Configuration of Hearing Loss

Now that we refreshed your knowledge on how to classify hearing loss according to its severity, let’s jump straight into the shape and pattern of your audiogram across the frequency spectrum (configuration of hearing loss). Many clinicians, especially audiologists, are able to immediately recognise what may be causing the hearing loss, as various configurations are associated with certain aetiologies of hearing loss. Below is a table presenting a commonly used classification system. 

 

Configuration

Description

Flat

Less than 5 dB difference per octave 

Gradually sloping

6 - 10 dB fall per octave

Steep / Marked / Sharply sloping

11 - 15 dB fall per octave 

Ski / Precipitously / Marked sloping

More than 15 dB fall per octave 

Gradually reverse sloping or rising slope

6 - 10 dB rise per octave

Steep / Marked / Sharply reverse sloping or rising slope

11 - 15 dB rise per octave 

Ski / Precipitously/Marked reverse sloping or rising slope

More than 15 dB rise per octave 

Corner/Fragmentary

Only a few low frequencies are audible - and the rest of the frequencies are severe to profound in loss

Cookie bite / Trough / Saucer

More than 20 dB loss in the middle frequencies than at 250 and 8000 Hz

Reverse cookie bite / Peaked

More than 20 dB loss at 250 or 8000 Hz than at middle frequencies

Notch

Sharply poorer threshold at one frequency, with recovery at adjacent frequencies

 

The configuration of the hearing loss will give you an idea of which sounds are heard best by the patient. A flat configuration, as indicated in the table above, is indicated by a hearing/ hearing loss that is horizontal (thresholds are more or less the same at all frequencies) and the thresholds do not differ by more than 5 dB from each other. A sloping configuration indicates an audiogram with better hearing thresholds in the lower frequencies (sometimes these frequencies show normal thresholds) compared to the higher frequencies. Contrary to this, a rising configuration indicates that high frequency sounds can be heard better than low frequency sounds. This is a rare type of audiogram and is quite complex to manage. A trough configuration (also known as cookie-bite) shows a hearing loss that is better in the mid frequencies compared to the lower and higher frequencies. This is usually a genetic loss and progressive in nature. Lastly, a notch (noise-notch) configuration indicates a hearing loss between 3000 and 6000 Hz, while lower and higher frequencies are not affected. This configuration normally indicates hearing loss due to excessive noise exposure. 

The above information is of paramount importance in the hearing healthcare field in terms of diagnosis and management of hearing loss.

The KUDUwave™ 

The KUDUwave™ audiometer provides information such as the degree of hearing loss and grade of hearing impairment by calculating them automatically. When viewing results the user can select to see the different ranges for the different grades/degrees.

KUDUwave software, which is free, comes with a module to create an interpretation for an audiogram in seconds.

KUDUwave plugin form for interpretations

 

Topics: Audiometer, Audiometry, Hearing loss, Audiology, Audiogram, Interpretations

 

Written by
Hlolo Ramatsoma
Hlolo Ramatsoma

Hlolo is a clinical, research & support Audiologist at eMoyo. He is involved in many parts of the business, from consulting to R&D to supporting and training customers. He earned his BSc in Audiology from the University of Cape Town and is an experienced clinical audiologist specialized in ototoxicity monitoring, product specialist and training audiologist.

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