ABR testing (auditory brainstem response testing) is a hearing test that measures how your auditory nerve and brainstem respond to sound. Unlike a standard hearing test where you raise your hand when you hear a beep, ABR requires no participation from the person being tested. Small sensors on the scalp pick up electrical activity generated by the hearing pathway within 10 milliseconds of a sound being played. This makes it one of the most reliable ways to evaluate hearing in newborns, young children, and anyone who can’t complete a traditional hearing exam.
How the Test Works
During an ABR test, small surface electrodes are placed on the scalp (usually at the top of the head) and on or near the earlobes. Earphones deliver a series of brief clicking sounds or tone bursts. Each time a sound enters the ear, it triggers a wave of electrical activity that travels from the inner ear along the auditory nerve and into the brainstem. The electrodes detect this activity and a computer averages the tiny signals together to create a waveform chart.
The resulting waveform has a series of peaks, labeled I through V, that each correspond to a specific location along the hearing pathway. Wave I reflects activity in the auditory nerve as it leaves the inner ear. Wave III originates in or near the cochlear nucleus, a relay station in the lower brainstem. Wave V, the most clinically important peak, is generated higher up in the brainstem. An audiologist examines how quickly each wave appears after the sound is played and how tall each peak is. Delayed or absent waves can pinpoint where a problem exists along the pathway.
Why Doctors Order an ABR
The most common reason is newborn hearing screening. Most hospitals in the United States screen every baby’s hearing before discharge, and ABR is one of the two technologies used for that purpose. Because the test doesn’t require the baby to respond or cooperate, it can be done while the infant sleeps in a bassinet.
Beyond newborn screening, ABR serves several other purposes:
- Estimating hearing thresholds in young children. Kids under about five often can’t sit through a full behavioral hearing test. ABR provides an objective estimate of how loud a sound needs to be before the brain registers it.
- Detecting auditory neuropathy. This is a condition where the inner ear detects sound normally but the auditory nerve doesn’t transmit the signal reliably to the brain. ABR is one of the few tests that can catch this.
- Screening for vestibular schwannoma (acoustic neuroma). A benign tumor on the hearing and balance nerve can delay or distort the ABR waveform. A meta-analysis of multiple studies found ABR detects these tumors with about 93% sensitivity overall, dropping to roughly 86% for tumors smaller than 1 centimeter. MRI remains more sensitive for small tumors, but ABR is a useful initial screen when one ear tests differently from the other.
- Cross-checking behavioral test results. If a standard hearing test produces unreliable or inconsistent results, ABR gives clinicians an objective comparison point.
How ABR Differs From OAE Screening
You may hear about another newborn hearing test called OAE (otoacoustic emissions). The key difference is where each test looks. OAE measures sounds produced by the outer hair cells in the inner ear. It confirms that the ear itself is working but doesn’t test anything beyond that point. ABR, on the other hand, tracks the signal all the way from the ear through the auditory nerve and into the brainstem.
This distinction matters because OAE can miss auditory neuropathy. A baby with that condition would pass an OAE screening (the inner ear is fine) but fail an ABR (the nerve isn’t transmitting properly). Many screening programs use one or both tests, and a failed screen on either one leads to more detailed follow-up.
What to Expect During the Test
For newborns, ABR screening is quick and painless. A nurse or audiologist places small adhesive sensors on the baby’s head, puts soft earphones in or over the ears, and runs the test while the baby sleeps. The automated version used in hospital nurseries takes only a few minutes per ear and gives a pass or refer result on the spot.
A diagnostic ABR, which maps out hearing thresholds at multiple frequencies, takes considerably longer. For infants under about six months, audiologists typically schedule the appointment around naptime or a feeding so the baby falls asleep naturally. Older babies and toddlers are a different story. Any movement, even sucking or eye blinking, creates electrical noise that interferes with the recording. For children over roughly six months who won’t sleep through the test on their own, sedation or general anesthesia is usually necessary.
At a facility like Children’s Hospital of Philadelphia, families are told to plan for up to five hours on the day of a sedated ABR. That includes check-in, sedation, the test itself, and recovery time afterward. A nurse typically calls beforehand to explain fasting instructions and the sedation process. In some cases, the audiologist will recommend that an ear, nose, and throat specialist see the child before or on the same day as the test, especially if fluid in the ears or other structural issues might affect results.
For adults, ABR is simpler. You lie back in a reclined chair, electrodes are placed on your scalp and earlobes, and you listen to clicking sounds through earphones. You don’t need to respond to the sounds. The test usually takes 30 to 60 minutes, no sedation required.
How Results Are Interpreted
The audiologist looks at three main features of the waveform: whether each wave is present, how long it takes to appear (its latency), and how large the peak is (its amplitude). At high sound levels, all five major waves should appear within about 10 milliseconds of the click.
Prolonged latencies, where a wave shows up later than expected, can indicate different things depending on which wave is delayed. If wave I is delayed, the problem likely starts in the inner ear or auditory nerve. If wave I is normal but later waves are delayed, the issue may be in the brainstem pathway itself. Absent waves at certain intensity levels help estimate hearing thresholds. The softest sound level that still produces a recognizable wave V is roughly correlated with the person’s hearing ability at that frequency, though correction factors are applied to convert the ABR result into an estimated behavioral hearing level.
Reduced wave I amplitude with a relatively preserved wave V has also drawn clinical interest as a possible marker of hidden hearing damage at the nerve fiber level, the kind that wouldn’t show up on a standard hearing test but might explain difficulty hearing in noisy environments. Standardized criteria for this type of diagnosis are still being developed.
Cost and Insurance Coverage
ABR testing is billed under specific medical codes that vary depending on the purpose of the test. An automated screening (the type used in newborn nurseries) is coded differently from a full diagnostic evaluation or a neurodiagnostic study looking for brainstem pathology. Most insurance plans cover ABR when it’s medically indicated, and newborn hearing screening is covered under preventive care mandates in most states. Without insurance, costs vary widely by facility and region, so calling ahead for a price estimate is worthwhile if you’re paying out of pocket. Sedation or anesthesia, when required for young children, is billed separately and adds to the total cost.