Defining a vitamin A deficiency cut‐off for retinol binding protein in Nepal children 6‐23 mo of age

Abstract

WHO defines vitamin A deficiency (VAD) as serum retinol <0.70 µmol/L. A standard cut‐off to categorize VAD using retinol binding protein (RBP) is not defined, thus, investigators often apply the retinol cut‐off to RBP. A population‐based survey in two Nepal districts assessed RBP among 2347 children 6–23 mo, and retinol among a randomly selected sub‐sample of 175 children. We examined the retinol‐RBP relationship among the sub‐sample to determine the appropriate RBP cut‐off for VAD in this population. Mean retinol and RBP concentrations were 0.82 µmol/L and 0.99 µmol/L, respectively. Using linear regression (Retinol = 0.8321*RBP – 0.0125 µmol/L; R2=0.45), a retinol cut‐off of 0.70 µmol/L corresponded to an RBP cut‐off 0.84 µmol/L. Using this calculated RBP cut‐off, the prevalence of VAD among the 2347 children was 27%. If the cut‐off <0.70 µmol/L had been used, the prevalence of VAD would have been underestimated, with a prevalence of 10%. Until a global cut‐off for RBP is established, surveys assessing RBP should measure retinol in a subsample of participants so a population‐specific cut‐off for RBP can be determined.