Salivary biomarkers are not suitable for pain assessment in newborns

Newborns admitted to the neonatal intensive care unit are repeatedly subjected to painful or stressful procedures; therefore, objective assessment of their pain is essential. An increasing number of scales for neonatal pain assessment have been developed, many of which are based on physiological and behavioral factors. Recently, salivary biomarkers have been used to assess stress in adults and older infants. This study aimed to determine whether salivary biomarkers can be useful objective indices for assessing newborn pain.

A total of 47 healthy newborns were enrolled 3-4days after birth. Heel lancing was performed to collect blood for a newborn screening test. Before and after heel lancing, saliva was collected to analyze hormone levels, a video was recorded for behavioral observations, and heart rate was recorded. Two investigators independently assessed newborn pain from the video observations using the Neonatal Infant Pain Scale (NIPS). Salivary chromogranin (sCgA) and salivary amylase (sAA) levels were measured using an enzyme-linked immunosorbent assay kit and a dry chemistry system, respectively.

No definite changes in salivary biomarkers (sCgA or sAA) were detected before and after heel lancing. However, newborn sCgA levels were markedly higher than reported adult levels, with large inter- and intra-subject variability, whereas newborn sAA levels were lower than adult levels. NIPS score and heart rate were dramatically increased after heel lancing.

NIPS score (behavioral assessment) and heart rate are useful stress markers in newborns. However, neither sCgA nor sAA is suitable for assessing newborn pain.