What are the relative merits of ABR and OAE for screening premature infants?
ABR can first be recorded at approximately 27 to 28 weeks conceptional age (Galambos & Hecox, 1978; Starr et al., 1977; Stockard and Westmoreland, 1981). The latency and amplitude is much more variable in premature infants than at term. In addition, the actual assignment of a gestational age by newborn medicine physicians is imprecise, with up to a two week margin of error. Infants in the neonatal and special care nurseries have a higher rate of transient effusion, which also creates problems for performing low level ABR. Lary et al. (1985) observed an ABR at click intensity levels in the range of 10 to 25 dB for infants with postconeceptional age of 40 weeks. In contrast, at a postconeptional age of 35 weeks, the average infant had an ABR threshold level of 30 dB. At 30 weeks, the average intensity level for ABR threshold was 40 dB. Unless you can tolerate a very high false positive rate in your screening program, screening at less than 35 weeks postconceptional age with a stimulus in the range of 35dBnHL would not be recommended. OAEs are not advised in the NICU or special care nursery for a variety of reasons: higher rates of middle ear effusion, higher levels of noise in the environment, higher levels of noise coming from the neonate. OAEs in this population will have a very high false positive rate. Therefore, we recommend screening with ABR at 35dBnHL at or greater than 35 weeks postconceptional age. If an infant is being discharged to home prior to 35 weeks, you would either need to arrange for screening on an outpatient basis (perhaps when they return for PKU testing) or screen them with the understanding that a 'pass' is unequivocal, but a 'refer' is qualified and requires repeat screening.
Roanne Karzon, Ph.D., CCC-A, is Manager of Audiology at St. Louis Children's Hospital, where she initiated the newborn hearing screening in 1988. She has several publications and presentations on the topic of newborn screenings.
Carole Campbell, M.S., CCC/A is audiology coordinator at St. Louis Children's Hospital (SLCH). Throughout the past 11 years, the major focus of her work at SLCH has been to oversee the newborn hearing screening program in the Neonatal Intensive Care Unit (NICU). More recently her efforts have included the implementation of screening programs throughout several BJC Health System hospitals. Carole also serves as a consultant/trainer for universal newborn hearing screening for the Missouri State Department of Health.