Hearing Loss Grades and the International Classification of Functioning, Disability and Health Bolajoko O Olusanya,A Adrian C Davisb & Howard J Hoffmanc

Perspectives

Hearing loss grades and the International classification of functioning, disability and health Bolajoko O Olusanya,a Adrian C Davisb & Howard J Hoffmanc

Hearing impairment negatively affects WHO’s first classification for hear- separate category for unilateral hearing well-being and is a major contributor to ing impairment dates to 1986 and is impairment was introduced and the six years lived with disability.1,2 The World based on the recommendations of an categories for bilateral hearing impair- Health Organization (WHO) estimates expert group established by WHO spe- ment were differentiated consistently by that 466 million people were living with cifically for this purpose; the classifica- 15-dB steps. The decision to reduce the disabling hearing impairment in 2018 tion has been modified several times limit for normal hearing was informed and this estimate is projected to rise to since then. The current one is shown by the extensive clinical experience of 630 million by 2030 and to over 900 mil- in Table 1; it is based on the version this expert group as well as available lion by 2050.3 However, these projec- published in 1991, which remarked that evidence in the literature at the time. tions are based on a hearing impairment persons with average pure-tone audi- While threshold of normal hearing set classification that does not fully reflect ometry of 15–20 decibels (dB) hearing at 15 dB could be found in the literature, the provisions of the International level may experience hearing problems, often resulting in an additional category classification of functioning, disability and those with unilateral hearing losses of slight impairment (16–25 dB hearing and health for assessing all forms of may experience hearing problems even level),8 the expert group opted not to functional impairments.4 Here we make if the better ear was normal.6 However, deviate from the International classifica- the case for a review of the concept of currently only adults (≥ 15 years) with a tion of functioning, disability and health disabling hearing loss adopted by WHO permanent unaided hearing impairment lowest generic qualifier of mild impair- after the recommendation of the Global above 40 dB hearing level in the better ment, but reduced the lower limit from Burden of Disease (GBD) Expert Group ear and children (from birth to 14 years 25 to 20 dB hearing level. This decision on Hearing Impairment in 2008. of age) with > 30 dB hearing level are was reinforced by the fact that persons The need for an independent clas- regarded as having a disabling hearing with hearing sensitivity < 20 dB rarely sification system for all impairments impairment.3 This classification raised benefit from or require amplification and disabilities as a complement to the three major concerns. First, the pre- devices, and was in agreement with the well-established International statisti- scribed threshold for normal hearing of remarks by the WHO expert group in cal classification of diseases and related 25 dB hearing level is not in agreement 1991.6 For example, one survey showed health problems, was first suggested in with several reports in the literature on that only 2.7% of a total of 556 026 hear- 1976 by the World Health Assembly. As the functional experience of persons ing aids dispensed over an undisclosed a result, in 1980 WHO developed the with slight or mild hearing impairment period were for persons with < 20 dB International classification of impair- (< 25 dB hearing level). Second, there hearing loss.8 Perhaps, most notable was ments, disabilities and handicaps.5 One is no scientific or rational basis for the the predominant use of this threshold of the key features of this system was the uneven steps between the various grades in sweep test audiometry, especially in use of qualifiers such as mild, moderate, of severity. Third, and more crucially, the school-aged children.9 severe and profound to distinguish vari- definition of disabling hearing impair- A separate category for unilateral ous levels of observed or measured de- ment excludes all persons with unilateral hearing impairment was introduced in viations outside of the range considered hearing impairment of any severity and line with the extensive literature on the for normal functioning for any health those with mild bilateral hearing impair- functional, educational, psychological condition. This categorization has been ment, which is not consistent with the or social impact of this type of hearing reinforced in the subsequent revisions International classification of function- impairment in all age groups.10 This to the system, such as the International ing, disability and health. category also reflected the International Classification of Functioning, Disability In 2008, the GBD Expert Group on classification of functioning, disability and Health, and accompanied with de- Hearing Loss addressed these concerns and health specific provisions for hear- scriptions of typical problems encoun- by reviewing the WHO classification ing problems associated with localiza- tered in daily activities at various levels for hearing impairment and other tion and lateralization, particularly in of severity.4 The classification, notably, data inputs for the GBD study 2010.7 difficult listening situations. The GBD does not use the term disabling, as it This assignment resulted in a proposal expert group proposed six categories for recognizes the needs of all persons with for a revised classification (Table 2). bilateral hearing impairment, differenti- functional impairments for appropriate The limit for normal hearing was re- ated consistently by 15-dB steps, since intervention. duced from 25 to 20 dB hearing level, a scientific or clinical evidence was lack-

a Centre for Healthy Start Initiative, 286A Corporation Drive, Dolphin Estate, Ikoyi, Lagos, Nigeria. b The Ear Institute, University College London, London, England. c Division of Scientific Programs, National Institute on Deafness and Other Communication Disorders, Bethesda, United States of America. Correspondence to Bolajoko O Olusanya (email: [email protected]). (Submitted: 20 January 2019 – Revised version received: 11 April 2019 – Accepted: 13 April 2019 – Published online: 3 September 2019 )

Bull World Health Organ 2019;97:725–728 | doi: http://dx.doi.org/10.2471/BLT.19.230367 725 Perspectives International classification for hearing loss Bolajoko O Olusanya et al.

Table 1. WHO’s Grades of hearing impairment

Grade of impair- Corresponding audiometric Performance Recommendations Comments added to the previous ment ISO valuea,b classification 0: no impairment 25 dB or better No or very slight hearing None 20 dB also recommended. problems. Able to hear People with 15 – 20 dB levels whispers may experience hearing problems. People with unilateral hearing losses may experience hearing problems even if better ear normal 1: slight 26–40 dB Able to hear and repeat Counselling. Hearing aids Some difficulty in hearing but impairment words spoken in normal may be needed can usually hear normal level of voice at 1 m conversation 2: moderate 41–60 dB Able to hear and repeat Hearing aids usually None impairment words using raised voice recommended at 1 m 3: severe 61–80 dB Able to hear some words Hearing aids needed. If Discrepancies between pure- impairment when shouted into better no hearing aids available, tone thresholds and speech ear lip-reading should be discrimination score should be taught noted 4: profound 81 dB or greater Unable to hear and Hearing aids may help Spoken speech distorted, the impairment understand even a in understanding words. degree depending on the age at including deafness shouted voice Additional rehabilitation which hearing was lost needed. Lip-reading and sometimes signing essential dB: decibel; Hz: Hertz; ISO: International Organization for Standardization; m: meter; WHO: World Health Organization. a In the better ear. b Average of 500, 1000, 2000 and 4000 Hz. Notes: Disabling hearing loss refers to hearing loss greater than 40 dB in the better hearing ear in adults (Grades 2, 3 and 4) and greater than 30 dB in the better hearing ear in children. Source: WHO.6

Table 2. Grades of hearing impairment as recommended by the Global Burden of Disease Expert Group on Hearing Loss

Category Pure-tone audiometrya,b Hearing experience in a quiet Hearing experience in a noisy environment environment Normal hearing −10.0 to 4.9 dB hearing level Excellent hearing Good hearing 5.0 to 19.9 dB hearing level Good hearing Rarely have difficulty in following/ taking part in a conversation Mild hearing loss 20.0 to 34.9 dB hearing level Does not have problems hearing May have real difficulty following/ what is said taking part in a conversation Moderate hearing loss 35.0 to 49.9 dB hearing level May have difficulty hearing a Has difficulty hearing and taking normal voice part in conversation Moderately severe hearing 50.0 to 64.9 dB hearing level Can hear loud speech Has great difficulty hearing and loss taking part in conversation Severe hearing loss 65.0 to 79.9 dB hearing level Can hear loud speech directly in Has very great difficulty hearing one’s ear and taking part in conversation Profound hearing loss 80.0 to 94.9 dB hearing level Has great difficult hearing Cannot hear any speech Complete or total hearing 95.0 dB hearing level or greater Profoundly deaf, hears no speech or Cannot hear any speech or sound loss loud sounds Unilateral < 20.0 dB hearing level in the better Does not have problems unless May have real difficulty following/ ear, 35.0 dB hearing level or greater sound is near poorer hearing ear taking part in a conversation in the worse ear dB: decibel; Hz:Hertz a In the better ear. b Average of 500, 1000, 2000 and 4000 Hz. Source: Global Burden of Disease Expert Group on Hearing Loss.7

726 Bull World Health Organ 2019;97:725–728| doi: http://dx.doi.org/10.2471/BLT.19.230367 Perspectives Bolajoko O Olusanya et al. International classification for hearing loss ing to support the variable steps between more benefit, especially in low-resource and health allows that, wherever pos- the grades in the WHO classifications. settings. The mere recognition of those sible, the person whose level of function- The choice of 15-dB was intended to with mild hearing impairment could ing is being classified (or the person’s reflect the minimum shift in pure-tone be advantageous, especially for school advocate) should have the opportunity audiometry thresholds that is typically children who may benefit from simple to participate and to challenge or con- considered as clinically and functionally but effective intervention such as pref- firm the appropriateness of the category significant, especially in occupational erential seating in the classroom. Such being used, and the assessment assigned. noise surveillance.11 recognition would also help parents and The proposed classification was The concept of disabling hearing carers to have better understanding of first reported in the 2010 GBD study to impairment also needed to be appro- the communication challenges children generate prevalence estimates and dis- priately expanded to include both uni- with mild hearing impairment face in ability weights for hearing impairment, lateral and bilateral hearing impairment their daily life. and has been adopted in all subsequent outside the range for normal hearing. Classifications based solely on GBD publications.2 A recent study spe- This was to ensure that the persons with pure-tone audiometry have limitations.8 cifically investigated the extent to which such impairment were not discrimi- For instance, while measurement of the revised pure-tone audiometry classi- nated against in accessing appropriate a behavioural pure-tone audiometry fication correlated with communication interventions. Calibrating the degree tests the entire auditory pathway, it deficits based on functional measures of difficulty in percentage terms across does not localize to any one segment of speech communication in the adult the various categories as suggested in along the auditory pathway. Hence, this population.12 The analysis showed good the International classification of func- measurement does not provide specific validity for the proposed classification tioning, disability and health is difficult. information on the status of the central system, based on the evidence from However, by definition, a condition is auditory nervous system and, therefore, relatively large population and clinical said to be disabling if it causes someone may offer only limited insight into au- studies. The analysis also established sig- to have an illness, injury or condition ditory function in real-world settings. nificant changes in functional commu- that makes it difficult to do the things Therefore, persons with normal pure- nication as the classification progresses that other people do. As a result of the tone audiometry thresholds can report from slight/mild through severe grades. expanded concept of disabling hearing having significant difficulties in hear- We recommend that WHO consid- impairment, it was no longer critical to ing. Concerns also exist regarding the ers adopting this revised classification have a separate classification for children various qualifiers attached to pure-tone to ensure that future WHO estimates (Table 1). audiometry thresholds such as normal of hearing impairment are aligned with However, the term disabling is nei- hearing or mild hearing impairment, as those published periodically in the ther recommended by International clas- these qualifiers do not always preclude GBD study and other epidemiological sification of functioning, disability and some degree of functional impairments.8 data. Doing so would also ensure that health nor routinely applied for other As a result, the proposed pure-tone au- no persons with functional hearing impairments. Therefore, discontinuing diometry categories should be comple- impairment, regardless of the severity, such description might be more appro- mented with descriptions of functional are unduly placed at a disadvantage priate from a practical, human rights performance that are not offensive or compared to those with other impair- and equity perspective. Conceiving an derogatory in any given cultural context ments within the framework of the In- impairment or disability that is not and that reflect activity limitation or ternational classification of functioning, disabling in all contextual factors is chal- participation restriction, particularly disability and health, especially under lenging. However, discontinuing the use in quiet and noisy environments. These the disability-inclusive global agenda of the term should not prevent a public categories should also include possible of the sustainable development goals. ■ health policy that prioritizes those for indications for rehabilitation with assis- whom hearing devices (hearing aids tive devices. Moreover, the International Competing interests: None declared. and cochlear implants) would provide classification of functioning, disability

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7. Stevens G, Flaxman S, Brunskill E, Mascarenhas M, Mathers CD, Finucane M; 10. Tharpe AM. Unilateral and mild bilateral hearing loss in children: past and Global Burden of Disease Hearing Loss Expert Group. Global and regional current perspectives. Trends Amplif. 2008 Mar;12(1):7–15. doi: http://dx.doi. hearing impairment prevalence: an analysis of 42 studies in 29 countries. org/10.1177/1084713807304668 PMID: 18270174 Eur J Public Health. 2013 Feb;23(1):146–52. doi: http://dx.doi.org/10.1093/ 11. National Institute of Occupational Safety and Health (NIOSH). publication eurpub/ckr176 PMID: 22197756 98-126: Available at: http://www.cdc.gov/niosh/docs/98-126/pdfs/98-126. 8. Clark JG. Uses and abuses of hearing loss classification. ASHA. 1981 pdf [cited 2019 April 1]. Jul;23(7):493–500. PMID: 7052898 12. Humes LE. The World Health Organization’s hearing-impairment grading 9. Bamford J, Fortnum H, Bristow K, Smith J, Vamvakas G, Davies L, et al. system: an evaluation for unaided communication in age-related hearing Current practice, accuracy, effectiveness and cost-effectiveness of the loss. Int J Audiol. 2019 Jan;58(1):12–20. doi: http://dx.doi.org/10.1080/1499 school entry hearing screen. Health Technol Assess. 2007 Aug;11(32):1–168, 2027.2018.1518598 PMID: 30318941 iii–iv. doi: http://dx.doi.org/10.3310/hta11320 PMID: 17683682

Corrigendum In: Health workforce burn out. Bull World Health Organ. 2019 Sep 1;97(9):585–86 on page 479, third column, the first sentence should read as follows: “…(Canada), with Australia and Ireland reporting proportions comparable to those in Canada.”

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