BACKGROUND: Salivary measurement of hormones and vitamins is gaining prominence as a minimally invasive procedure with the negligible potential for harm. We aimed to assess the utility of saliva for assessing vitamin A status in extremely preterm infants.
METHODS: Paired saliva and blood samples were collected at 4 weeks of age from infants born <28 weeks of gestation using a proprietary polymer swab. Plasma retinol was measured using high-performance liquid chromatography, and salivary retinol was measured using enzyme-linked immunosorbent assay.
RESULTS: Thirty infants were recruited with a median (IQR) gestation and birth weight of 26.2 weeks (24.8-27.2) and 865 g (718-1,002), respectively. An adequate volume of saliva (>50 µL) was obtained in 68%. There was no significant correlation (Spearman's correlation coefficient = 0.16, p = 0.3) between individual plasma and salivary retinol levels. Bland-Altman analysis showed wide limits of agreement (-113 to +119%) between individual plasma and salivary retinol levels.
CONCLUSION: Individual vitamin A status cannot be determined reliably from saliva in extremely preterm infants using current collection materials and analysis techniques.