BAER testing (Brainstem Auditory Evoked Response) is a non-invasive hearing test that measures how sound travels from your inner ear through the auditory nerve and into your brainstem. Unlike a standard hearing test where you raise your hand when you hear a tone, BAER doesn’t require any response from the person being tested. That makes it especially useful for newborns, young children, and anyone who can’t participate in a traditional hearing exam. It’s also widely used in veterinary medicine to screen dogs for congenital deafness.
How the Test Works
Small adhesive sensors are placed on the forehead and behind each ear. Earphones then deliver a series of clicking sounds, and the sensors pick up the tiny electrical signals your brain generates in response. A computer averages thousands of these responses to produce a waveform with five distinct peaks, each representing a different stop along the auditory pathway from the ear to the brainstem.
The first peak reflects activation of the auditory nerve fibers in the inner ear. The second corresponds to the cochlear nucleus, where sound signals first get processed. The third peak comes from a brainstem structure involved in comparing sounds between your two ears. The fourth represents a relay pathway carrying information upward toward higher brain centers. The fifth and final peak reflects a structure responsible for processing sound location and integrating auditory information. By measuring how quickly each peak appears (in milliseconds) and how large it is, clinicians can pinpoint exactly where along this pathway something might be going wrong.
What Normal Results Look Like
Each wave should appear within a narrow time window after the click. In healthy adults, the first wave typically shows up around 1.5 to 1.65 milliseconds, the third wave around 3.73 to 3.92 milliseconds, and the fifth wave around 5.49 to 5.67 milliseconds. The gaps between waves matter too. The interval from wave I to wave V normally falls between about 3.9 and 4.0 milliseconds. If any of these peaks are delayed, missing, or abnormally shaped, it signals a problem at that specific point in the auditory pathway.
What BAER Testing Can Detect
The test’s real strength is that it goes beyond the ear itself. A standard hearing test tells you whether someone can hear, but BAER testing shows where the signal breaks down. This makes it valuable for diagnosing several conditions:
- Hearing loss in newborns and infants who can’t respond to behavioral hearing tests
- Auditory neuropathy, a condition where the inner ear detects sound normally but the auditory nerve doesn’t transmit it properly to the brain
- Acoustic neuromas, benign tumors on the auditory nerve that delay signal transmission
- Multiple sclerosis and other demyelinating conditions that damage nerve insulation in the brainstem
- Brainstem lesions or strokes that disrupt auditory processing
This is one key advantage BAER has over another common hearing screen called otoacoustic emissions (OAE). OAE testing measures the function of tiny hair cells in the inner ear but doesn’t evaluate the auditory nerve at all. That means OAE can miss auditory neuropathy entirely, while BAER catches it.
What to Expect During the Test
The person being tested needs to be very still and quiet, ideally asleep. For newborns, this is usually straightforward since they sleep naturally during the test. Babies older than about six months, though, often need sedation or general anesthesia because they won’t hold still long enough. Children’s Hospital of Philadelphia advises parents to plan for up to five hours at the facility when sedation is involved, accounting for preparation, the sedation process, the test itself, and recovery time.
The test is painless. Three small sticker sensors go on the skin (forehead and behind each ear), earphones are placed, and the computer does the rest. You won’t feel the clicks or the recording. For adults, the main requirement is relaxing and staying still, sometimes with eyes closed in a reclining chair.
BAER Testing in Newborn Hearing Screening
Most hospitals in the United States screen every newborn’s hearing before discharge, and BAER is one of the two technologies used for this. The screening version is simplified: it checks hearing at only one loudness level and gives an automated pass or fail result. If a baby fails the screening, a full diagnostic BAER test follows. The diagnostic version tests multiple loudness levels, evaluates both ears independently, and produces the detailed waveform that an audiologist interprets. Around two to three out of every 1,000 newborns are born with hearing loss in one or both ears, so catching it early through screening has a significant impact on language development.
BAER Testing for Dogs
BAER testing is the only definitive way to diagnose deafness in dogs, particularly congenital deafness that’s present from birth. Congenital deafness has been reported in roughly 80 breeds, and the list keeps growing. Breeds with white pigmentation are at the highest risk, especially those carrying the merle gene (Collies, Shetland Sheepdogs, Harlequin Great Danes, Old English Sheepdogs) or the piebald gene (Bull Terriers, Dalmatians, English Setters, Beagles, Greyhounds, Great Pyrenees).
Dalmatians have the highest incidence of any breed: 8% are deaf in both ears and 22% are deaf in one ear. English Setters, English Cocker Spaniels, Australian Cattle Dogs, and Bull Terriers have rates roughly one-third to one-half that of Dalmatians. Catahoulas and Australian Shepherds also show high rates. Puppies can be reliably BAER tested starting at 35 days old, according to the Orthopedic Foundation for Animals. Dogs that are deaf in only one ear often go undetected without testing since they compensate well, which is why breeders of high-risk breeds routinely screen entire litters.
Cost of BAER Testing
For humans, the cost varies depending on whether you’re getting a limited or comprehensive test. VA outpatient facility charges list comprehensive auditory evoked potentials (the full diagnostic BAER) at roughly $1,648 and limited testing at about $885, though what you actually pay depends heavily on your insurance, the facility, and whether the test is done in a hospital versus a private audiology office. Many insurance plans cover BAER testing when it’s medically indicated, particularly for newborn screening or neurological workups. For dogs, veterinary BAER testing typically runs between $100 and $400 per animal, varying by clinic and location.