The effect of short‐term frozen storage of human milk on the validity of Vitamin A assays using the iCHECKTM rapid analyzer

Background Breast milk retinol concentration is an indicator of both infant nutrient intake and population vitamin A status. Milk is easily and non‐invasively collected and rapid field methods for vitamin A analysis now exist. Objective To confirm or refute the assertion of restricting fluorescent assaying of milk vitamin A to “unfrozen” samples (Schweigert et al, Sight & Life Magazine 2011 (2) 18–22). Methods Full‐breast expression milk samples were collected in 21 women from Mam ‐Mayan rural communities in the Western Highlands of Guatemala. A milk‐fat packing volume (creamatocrit), expressed in volume percent (vol%), was measured on a hematocrit microcentrifuge. Retinol concentration was assayed, both fresh and after 20–26 d at −20°C, on an iCHECK TM rapid field analyzer (Bioanalyt, Telbow, Germany). Results Respective retinol concentrations were 539±221 μg/L (fresh) and 528±205 μg/L (post‐freezing) (p=0.45), with a Pearson correlation coefficient (P) and Spearman coefficient (S) both of r=0.959 (p=0.001). The corresponding values for creamatocrit were 8.1±3.1 vol% vs 9.0±4.0 vol% (p=0.17), with r=0.774 (p=0.001)(P) and r=0.844 (p=0.001)(S). Conclusions Milk samples can be stored for at least 3 wks without affecting the validity of iCHECK TM assays. Funded by Sight & Life of Basel and Tufts University School of Medicine