ABR: the test that measures hearing without requiring a response

What does ABR measure?

ABR stands for auditory brainstem response. When sound reaches the ear, it generates an electrical impulse that travels along the auditory nerve and the brainstem. The test captures that impulse through electrodes placed on the skin and records the timing and amplitude of each stage of the journey.

This allows two things: estimating hearing threshold — the faintest sound that still generates a response — and checking whether the auditory pathway is conducting the signal normally.

When is it indicated?

• Newborns and babies who did not pass hearing screening.
• Children with delayed speech, where audiometry is not feasible.
• People unable to cooperate with conventional audiometry.
• Investigation of asymmetric hearing loss, affecting one side only.
• Suspected abnormality of the auditory pathway.

How is it carried out?

1. The skin of the forehead and behind the ears is cleaned and adhesive electrodes are applied.
2. Headphones are placed on the ears.
3. The patient lies still and at rest — silence and stillness matter, which is why the test is carried out with babies asleep.
4. Sequences of clicks at different intensities are presented, and the equipment records the responses.

Movement and muscle tension create interference. This is why sleep preparation, in the case of children, makes such a difference to the result.

With or without sedation?

The test requires silence and stillness, because movement and muscle tension interfere with the recording. There are two ways of achieving that, and Clínica Rhinus works with both:

• Natural sleep. The first choice in babies and young children. It depends on arriving at the time the child usually sleeps, fed and tired — hence the importance of preparation.
• Under sedation. Indicated where the child does not fall asleep naturally, wakes easily, or cannot stay still for long enough. At the clinic, sedation is carried out with an anaesthetist present, who monitors the patient throughout the test.

Where the test is booked under sedation, there is fasting to observe and the patient must come accompanied by an adult. The team gives these instructions at the time of booking.

What does the result show?

The report presents the recorded waveforms, the intervals between them and the estimated threshold for each ear. Interpretation is carried out by the ENT specialist alongside the other hearing tests and the clinical history.

At Clínica Rhinus, the test is performed by the speech-language pathologists on our team, and the result is discussed at the consultation.

How should I prepare for this test?

• Bring the medical request: it is required for all tests, whether under insurance or self-pay.
• In babies and young children the test is done during natural sleep — arrive with the child tired and fed.
• Wash the hair beforehand and do not use gel, cream or oil, which interfere with electrode contact.
• Do not use make-up, sunscreen or moisturiser on the face on the day of the test: they interfere with electrode contact.
• Bring whatever helps the child sleep: bottle, dummy, blanket, the usual toy.
• Bring any previous hearing tests for comparison.
• If the test is booked under sedation, follow the fasting instructions given by the team and come accompanied by an adult.

Sources: Brazilian Association of Otorhinolaryngology and Cervico-Facial Surgery (ABORL-CCF) · Flint PW, Francis HW, Haughey BH, et al. Cummings Otolaryngology: Head and Neck Surgery. 7th ed. Elsevier; 2020. · Bento RF, Bittencourt AG, Voegels RL. Seminários em Otorrinolaringologia. Fundação Otorrinolaringologia.