Otoacoustic Emissions Test

What Are Otoacoustic Emissions?

Otoacoustic emissions (OAEs) are faint sounds naturally produced by the outer hair cells of the cochlea — the snail-shaped sensory organ of the inner ear — as part of the normal hearing process. These microscopic cells do not simply receive sound passively; they actively amplify and sharpen incoming sound signals, acting as tiny biological amplifiers that boost quiet sounds by as much as 40–60 dB and enhance the ear`s ability to distinguish closely spaced frequencies. A by-product of this active process is the generation of faint acoustic energy — otoacoustic emissions — that travels back out through the middle ear and eardrum into the ear canal, where it can be detected by a sensitive microphone placed at the ear canal opening.

The discovery of otoacoustic emissions in 1978 by British physicist David Kemp at University College London was one of the most significant breakthroughs in the history of hearing science. For the first time, it became possible to objectively assess the function of the cochlea without requiring any behavioural response from the patient — no button pressing, no hand raising, no verbal reply. This made OAE testing uniquely valuable for populations who cannot participate in conventional audiometry: newborn babies, infants, young children, adults with severe learning difficulties, and patients under sedation or anaesthesia.

In the UK, OAE testing is now one of the most widely performed hearing assessments. It is the cornerstone of the NHS Newborn Hearing Screening Programme (NHSP), which screens over 98% of all babies born in the country within their first few weeks of life. It is also an essential component of diagnostic audiology, ototoxicity monitoring, noise damage surveillance, and the investigation of auditory processing disorders. The test is quick, completely painless, and provides immediate, objective results that complement the broader hearing assessment.

How the Cochlea Produces Otoacoustic Emissions

Understanding why the cochlea generates sounds requires a brief look at how hearing works at the cellular level. The cochlea contains approximately 12,000 outer hair cells and 3,500 inner hair cells, arranged in rows along the basilar membrane. When sound enters the cochlea, it creates a travelling wave along the basilar membrane. Different frequencies cause the membrane to vibrate at different locations — high frequencies near the base, low frequencies near the apex — a principle known as tonotopic organisation.

The outer hair cells respond to these vibrations with a remarkable ability: they can change their length at extraordinary speed — up to tens of thousands of times per second — in a process called electromotility. This mechanical amplification boosts the vibration of the basilar membrane at the point where a given frequency is being processed, sharpening the frequency selectivity and amplifying quiet sounds so that the inner hair cells can detect them. The inner hair cells are the true sensory receptors — they convert the amplified mechanical vibration into electrical nerve impulses that travel along the auditory nerve to the brain.

The outer hair cell amplification process is not perfectly efficient. Some of the mechanical energy generated by the outer hair cells travels backwards — from the cochlea through the middle ear to the eardrum and into the ear canal. These backward-travelling signals are otoacoustic emissions. Their presence confirms that the outer hair cells are alive, motile, and functioning. Their absence or reduction indicates outer hair cell damage — the hallmark of the most common form of sensorineural hearing loss.

Types of OAE Test — TEOAE vs DPOAE

Two main types of OAE test are used in clinical audiology, each with distinct characteristics and applications:

Transient Evoked Otoacoustic Emissions (TEOAEs)

TEOAEs are elicited by presenting brief click stimuli through a probe in the ear canal. The click stimulates a broad region of the cochlea simultaneously, and the emissions generated in response are recorded by the probe microphone in the milliseconds following each click. By averaging responses to hundreds or thousands of clicks, the recording equipment extracts the OAE signal from background noise.

TEOAEs provide a broad-frequency assessment of cochlear function, typically covering the range from approximately 1,000 Hz to 4,000 Hz. They are present in virtually all ears with normal hearing or hearing thresholds better than approximately 30 dB HL. When hearing loss exceeds this level — indicating significant outer hair cell damage — TEOAEs are typically absent.

TEOAEs are the method used in the NHS Newborn Hearing Screening Programme, where the Automated Otoacoustic Emissions (AOAE) device presents clicks and uses an algorithm to determine whether emissions are present (a `pass` result) or absent (a `refer` result requiring further assessment). The simplicity, speed, and reliability of the TEOAE technique make it ideally suited to large-scale population screening.

Distortion Product Otoacoustic Emissions (DPOAEs)

DPOAEs are generated using a different approach. Two continuous tones at closely spaced frequencies — called f1 and f2 — are presented simultaneously through the ear canal probe. The interaction of these two tones within the cochlea produces a third tone — the distortion product — at a frequency mathematically related to the two primaries (specifically, at 2f1 – f2). This distortion product is an otoacoustic emission that the probe microphone records.

The key advantage of DPOAEs is their frequency specificity. By varying the frequencies of f1 and f2, the audiologist can probe the function of outer hair cells at specific locations along the cochlea, producing a DPOAEgram — a graph showing emission strength at each tested frequency, typically from 1,000 Hz to 8,000 Hz or higher. This makes DPOAEs particularly valuable for:

• Monitoring cochlear function over time: Serial DPOAE testing can detect subtle changes in outer hair cell function that precede changes on the pure tone audiogram
• Ototoxicity monitoring: Tracking cochlear damage in patients taking drugs that can harm hearing
• Early detection of noise-induced cochlear damage: Identifying outer hair cell loss before it reaches the threshold for audiometric hearing loss
• Frequency-specific cochlear assessment: Mapping the pattern of cochlear damage across the frequency range

How the OAE Test Is Performed

The OAE test procedure is one of the simplest and quickest in all of audiology:

Equipment

The audiologist uses a handheld OAE probe — a small device about the size of a pen, fitted with a soft rubber or foam tip. The probe contains a miniature loudspeaker (to deliver the stimulus sounds) and a highly sensitive microphone (to record the emissions). The probe is connected to a processing unit — often a laptop or a dedicated handheld device — that controls the stimuli, records and analyses the emissions, and displays the results in real time.

Procedure

A soft probe tip of appropriate size is selected and gently placed into the opening of the ear canal, creating a comfortable, snug seal. The seal is important because it keeps external noise out and ensures the stimulus sounds are delivered efficiently. Once the seal is achieved, the device automatically plays the stimulus (clicks for TEOAEs, or paired tones for DPOAEs) and begins recording the emissions.

For each ear, the test takes approximately 1 to 3 minutes. Both ears are tested, making the total test time typically 5 to 10 minutes including set-up. The patient does not need to do anything — there is no button to press, no hand to raise, no response required at all. The only requirement is to sit or lie quietly and still, as noise from talking, coughing, swallowing, or movement can mask the faint emissions and reduce the quality of the recording.

Comfort

The test is completely painless. Most patients are unaware that anything is happening — they may hear faint clicking or humming from the probe, but there is no discomfort whatsoever. For newborns and infants, the test is ideally performed while the baby is sleeping — most babies sleep through the entire procedure without stirring.

What OAE Results Tell Us About Cochlear Function

OAE results are interpreted in the context of the broader audiological assessment, but the core principle is straightforward:

• Present, robust OAEs: The outer hair cells at the tested frequencies are functioning normally. This strongly suggests that the cochlea is healthy at those frequencies. OAEs are typically present when hearing thresholds are better than approximately 25–30 dB HL.
• Reduced OAEs: Some outer hair cell damage may be present, or the recording conditions may have been suboptimal (background noise, poor probe seal, middle ear dysfunction). Reduced emissions warrant further investigation with pure tone audiometry and tympanometry.
• Absent OAEs: The outer hair cells at the tested frequencies are significantly damaged or non-functional. This is consistent with a sensorineural hearing loss of approximately 30 dB HL or greater at those frequencies. Absent OAEs in the presence of normal middle ear function confirm cochlear pathology.

It is important to note that OAEs require normal middle ear function to be recorded. If the middle ear is impaired — for example, by glue ear, middle ear infection, or impacted ear wax — the emissions generated by the cochlea may be blocked or attenuated before they reach the probe microphone, producing a false-negative result (absent OAEs despite healthy outer hair cells). For this reason, tympanometry is often performed alongside OAE testing to confirm that the middle ear is clear.

The Role of OAEs in Newborn Hearing Screening

The single most impactful application of OAE testing is in newborn hearing screening. The NHS Newborn Hearing Screening Programme (NHSP) uses Automated Otoacoustic Emissions (AOAE) as its first-line screen for all babies born in the UK. The programme was rolled out nationally in England in 2006 and now screens over 700,000 babies per year across the UK, with coverage rates exceeding 98%.

The AOAE test is performed by a trained hearing screener, usually on the postnatal ward within hours or days of birth. The automated device presents click stimuli and uses a statistical algorithm to determine whether the emissions exceed background noise at a level consistent with normal cochlear function. The result is binary: pass (clear response detected, indicating normal outer hair cell function) or refer (no clear response, indicating the need for further assessment).

Approximately 1 to 2 babies in every 1,000 are born with permanent hearing loss (RNID). Before universal screening, the average age of identification was around 18 months to 3 years — well past the critical window for speech and language development. With the NHSP, most affected babies are now identified before three months of age and enrolled in intervention by six months, in line with the internationally recognised 1-3-6 guideline (screen by 1 month, diagnose by 3 months, intervene by 6 months). Babies who do not pass the AOAE screen are referred for an Automated Auditory Brainstem Response (AABR) test, which assesses the auditory nerve pathway and can detect conditions that OAEs alone may miss.

OAEs in Differential Diagnosis and Hidden Hearing Loss

Beyond newborn screening, OAE testing plays a critical role in diagnostic audiology by helping to localise the site of auditory dysfunction:

Differentiating Cochlear from Retrocochlear Pathology

One of the most clinically important uses of OAEs is distinguishing between sensory (cochlear) and neural (retrocochlear) hearing loss. In cochlear hearing loss — caused by outer hair cell damage from ageing, noise, or ototoxic drugs — OAEs are absent because the damaged cells cannot generate emissions. In retrocochlear hearing loss — caused by problems with the auditory nerve or brainstem, such as acoustic neuroma (vestibular schwannoma) — OAEs may be present because the outer hair cells are intact, even though the nerve cannot transmit signals properly. This pattern of present OAEs with abnormal ABR waveforms and poor speech understanding is a hallmark of auditory neuropathy spectrum disorder (ANSD).

Detecting Hidden Hearing Loss

The concept of "hidden hearing loss" — clinically known as cochlear synaptopathy — has generated significant research interest in recent years. In this condition, the synaptic connections between the inner hair cells and the auditory nerve fibres are damaged (typically by noise exposure or ageing), but the outer hair cells remain intact. The result is a normal audiogram and normal OAEs, but significant difficulty understanding speech in background noise. While OAEs cannot directly detect synaptopathy (because the outer hair cells are unaffected), the finding of normal OAEs in a patient with significant speech-in-noise difficulty points the clinician towards this diagnosis and away from outer hair cell pathology. It also underscores the importance of combining OAE testing with other assessments — particularly speech-in-noise testing and ABR — for a complete diagnostic picture.

Ototoxicity Monitoring — Protecting Hearing During Treatment

Certain medications used in the treatment of serious conditions can damage the outer hair cells of the cochlea — a side effect known as ototoxicity. The most common ototoxic drugs encountered in UK clinical practice include:

• Platinum-based chemotherapy agents: Cisplatin and carboplatin, used in the treatment of many cancers, are among the most ototoxic drugs in clinical use. The British Society of Audiology (BSA) estimates that ototoxic hearing loss occurs in 40–80% of patients receiving cisplatin, depending on dose and individual susceptibility
• Aminoglycoside antibiotics: Gentamicin, tobramycin, amikacin, and streptomycin, used to treat serious bacterial infections, particularly in neonatal intensive care and cystic fibrosis management
• Loop diuretics: Furosemide, particularly when administered intravenously at high doses or in combination with aminoglycosides

DPOAE testing is one of the most sensitive tools for monitoring ototoxicity. Serial DPOAEs can detect outer hair cell damage at an earlier stage than conventional audiometry, allowing clinicians to modify drug dosing, switch to less ototoxic alternatives, or prepare the patient for hearing rehabilitation. The BSA and NICE both recommend ototoxicity monitoring protocols that include DPOAE testing, particularly for patients receiving cisplatin-based chemotherapy. In practice, baseline OAEs are recorded before treatment begins, and follow-up OAEs are recorded at intervals during and after treatment to track any changes.

Advantages and Limitations of OAE Testing

Key advantages

• Completely objective: No patient response required — ideal for newborns, infants, and patients who cannot cooperate with behavioural tests
• Quick: Each ear takes just 1 to 3 minutes — faster than virtually any other audiological assessment
• Non-invasive and painless: No discomfort, no sedation, no risk
• Sensitive to early damage: DPOAEs can detect outer hair cell damage before it produces a measurable hearing loss on the audiogram
• Frequency-specific: DPOAEs can map cochlear function across the frequency range
• Portable: Modern OAE equipment is handheld and battery-powered, enabling testing at the bedside, in schools, in mobile screening units, and at the patient`s home
• Highly reproducible: OAE results are stable in healthy ears, making serial monitoring meaningful and reliable

Limitations

• Requires normal middle ear function: Middle ear pathology (fluid, infection, wax, perforation) can block emissions and produce false-negative results. Tympanometry should be performed alongside OAEs to verify middle ear status
• Does not measure hearing thresholds: OAEs confirm outer hair cell function but do not tell you how quietly a person can hear — pure tone audiometry is still needed for threshold measurement
• Cannot detect retrocochlear or neural hearing loss: OAEs only assess the outer hair cells. Conditions affecting the auditory nerve (such as auditory neuropathy or acoustic neuroma) may produce normal OAEs despite significant hearing difficulty. ABR testing is needed to assess neural pathways
• Sensitive to environmental noise: Background noise in the test environment can mask faint emissions. OAE testing should ideally be performed in a quiet room
• Limited above approximately 30 dB HL: OAEs are typically absent when hearing loss exceeds 25–30 dB HL, making them less useful for quantifying the degree of established hearing loss

Where to Get an OAE Test in the UK

OAE testing is widely available across the UK:

• NHS Newborn Hearing Screening: AOAE testing is performed free of charge for all newborn babies as part of the NHSP. No referral is needed — the screening is offered routinely
• NHS audiology departments: OAE testing is included in diagnostic hearing assessments at NHS audiology clinics, accessed via GP or consultant referral. It is performed free of charge as part of the assessment
• Private audiology clinics: Many private audiologists include OAE testing in their comprehensive hearing assessments. Providers such as Boots Hearingcare, Specsavers Audiology, and specialist paediatric or ototoxicity clinics routinely offer OAE testing, usually at no additional cost beyond the hearing assessment fee
• Occupational health: Some occupational hearing test programmes include DPOAEs as a supplement to standard audiometry for workers exposed to hazardous noise levels

Use our search tool to find audiologists near you who offer comprehensive hearing assessments including OAE testing. Whether you are a parent concerned about your newborn`s hearing, a patient undergoing ototoxic treatment, a musician worried about noise exposure, or an adult seeking a thorough hearing evaluation, OAE testing provides a rapid, painless, and clinically powerful window into the health of your inner ear. It is one of the most elegant tests in all of medicine — listening to the sounds your own ear produces to understand how well it hears.