We read with great interest the recently published article by Fares et al. in which the authors evaluated changes in plasma vitamin A, E and D concentrations during the early postnatal life and their link with growth and mortality in Tunisian very low birth weight (VLBW) infants [Citation1]. Their findings suggest that current nutritional practices are ineffective to achieve adequate vitamins A, E and D status in Tunisian VLBW infants during the early postnatal life and should be revised. The study is important because it provides scientific information on this clinically relevant condition. However, we think that some issues should be discussed.
In the original study, VLBW infants (birth weight <1500 g and gestational age <37 weeks) admitted in the Centre of Maternity and Neonatology of Tunis between 2005 and 2008 were followed from birth until hospital discharge or death. As indicated in the “Methods” section, the 25-hydroxyvitamin D (25(OH)D) levels in this study population were measured by competitive radioimmunoassay after acetonitrile extraction (DiaSorin Inc., Stillwater, MN). The method use 125I-labelled 25(OH)D, an antibody to 25(OH)D and a second antibody for precipitation and allows the combined measurement of both 25(OH)D3 and 25(OH)D2. However, according to kit specifications % cross-reactivity with the 3-epi-25(OH)D3 is not specified. In recent years, certain liquid chromatography tandem mass spectrometry (LC–MS/MS)-based methods with higher sensitivity and specificity have also come into prominence and are gaining wide-spread acceptance in 25(OH) D measurement. Labor intensive and non-automated radioimmunoassay methods were not preferred by clinical laboratories for the assessment of 25(OH)D concentration [Citation2]. Although, interpretation of assay results is further complicated by proprietary antibodies having different affinities for vitamin D metabolites or epimers, such as 24,25-dihydroxyvitamin D (24,25(OH)2D) or C-3 epimer of 25(OH)D (3-epi-25(OH)D3) [Citation3]. Plasma concentrations of 24,25(OH)2D have been reported to be low (<10 nmol/L) and represent <6% of circulating 25(OH)D; however, 3-epi-25(OH)D3 has been detected in 20–98% of infants using LC–MS/MS and may represent up to 40% of total plasma 25(OH)D measured in young infants [Citation2]. Therefore, in studies performed in VLBW infants, it should be better to evaluate 25(OH)D levels by LC-MS/MS in order to avoid falsely elevated results originating from C-3 epimers.
In conclusion, the 25(OH)D results obtained by LC-MS/MS methods could provide more accurate data about VLBW infants. And this would provide a better understanding of the relationship between the levels of serum vitamin D and growth and mortality in Tunisian VLBW infants during the early postnatal life.
Declaration of interest
The authors state that there is no conflict of interest regarding the publication of this paper.
This study received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
References
- Fares S, Feki M, Khouaja-Mokrani C, et al. Nutritional practice effectiveness to achieve adequate plasma vitamin A, E and D during the early postnatal life in Tunisian very low birth weight infants. J Matern Fetal Neonatal Med 2014;10:1–5
- Singh RJ, Taylor RL, Reddy GS, et al. C-3 epimers can account for a significant proportion of total circulating 25-hydroxyvitamin D in infants, complicating accurate measurement and interpretation of vitamin D status. J Clin Endocrinol Metab 2006;91:3055–61
- Gallo S, Comeau K, Agellon S, et al. Methodological issues in assessing plasma 25-hydroxyvitamin D concentration in newborn infants. Bone 2014;61:186–90