Normal ABR Threshold in Newborns
Normal ABR thresholds in newborns are approximately 0-20 dB nHL (normalized hearing level), with most healthy full-term newborns demonstrating thresholds below 40 dB nHL 1, 2.
Key Threshold Values
The American Academy of Pediatrics guidelines establish that air-conduction hearing threshold levels greater than 20 dB at any frequency indicate possible hearing loss and warrant referral to a pediatric audiologist 1. This 20 dB nHL cutoff serves as the clinical standard for defining normal versus abnormal hearing in the pediatric population.
Age-Specific Considerations
Research demonstrates important maturational effects on ABR thresholds in the immediate postnatal period:
- Newborns <48 hours old: Mean ABR thresholds are elevated at approximately 14.5 dB nHL (51.5 dB peak SPL) for air-conducted clicks, likely due to residual middle ear fluid and vernix 3
- Newborns 49-96 hours old: Thresholds improve significantly to 3.8 dB nHL (40.8 dB peak SPL) as middle ear fluids resolve 3
- After 96 hours: Thresholds stabilize at 3.75 dB nHL, comparable to adult values 4
Clinical Screening Standards
For newborn hearing screening programs using ABR:
- 85% of normal newborns have ABR thresholds <40 dB nHL
- 54% have thresholds <20 dB nHL
- An adequate screening level is 30-40 dB nHL 5
The AAP guidelines emphasize that ABR testing in newborns should use frequency-specific tone bursts across multiple frequencies to create an audiogram-like map of hearing sensitivity 1, 2. This provides more diagnostic information than click-evoked ABR alone.
Important Clinical Caveats
ABR is not a true test of hearing because it measures auditory pathway structural integrity rather than cortical processing of sound 1. Even with normal ABR results, behavioral audiometry remains the gold standard for confirming functional hearing.
Gender Differences
Research shows female newborns have significantly lower (better) ABR thresholds than males, though the clinical significance is modest 6. This should be considered when interpreting borderline results.
Bone Conduction Values
For bone-conducted ABR in newborns:
- Mean threshold: 1.25-1.8 dB nHL (36-37 dB peak re: 1 microN) 3, 4
- Bone conduction thresholds remain stable across the first 96 hours, unlike air conduction 3
- This difference helps identify transient conductive hearing loss from middle ear fluid in the immediate postnatal period
Practical Algorithm for Interpretation
- If ABR threshold ≤20 dB nHL: Normal hearing, no further action needed
- If ABR threshold 21-40 dB nHL: Possible mild hearing loss or transient conductive component; repeat testing recommended
- If ABR threshold >40 dB nHL: Definite hearing loss; immediate referral to pediatric audiologist for comprehensive evaluation 1, 2
For infants <48 hours old with elevated air conduction thresholds but normal bone conduction thresholds, consider physiologic conductive deficit from residual middle ear fluid and retest after 48-96 hours 3.
The Joint Committee on Infant Hearing mandates that any infant who does not pass screening should receive comprehensive audiological evaluation by 3 months of age to enable intervention before the critical period for speech and language development 2.