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Published on: May 16, 2019
A Rapid Colorimetric Method for Determining Calcium, Inorganic Phosphorus, and Zinc in Human Milk Using Clinical
Miori Tanaka1, Misaki Mochida1, Midori Date1
1The Nippon Foundation Human Milk Bank, Tokyo, Japan.
Background:
Calcium (Ca), inorganic phosphorus (IP), and zinc (Zn) are essential minerals in human milk for infant growth and health. Current methods for determining minerals in human milk, including inductively coupled plasma atomic emission spectroscopy (ICP-AES), are time-consuming and laborious. This study aimed to measure Ca, IP, and Zn in human milk by a rapid, simple, and accurate method using clinical laboratory reagents based on a colorimetric assay.
Methods:
71 pooled donor human milk (DHM) samples were collected after Holder pasteurization. The only pretreatment required was dilution, and samples were diluted 5-fold. Ca, IP, and Zn concentrations were measured by colorimetric assay using an automated analyzer. The results were validated in terms of repeatability, recovery, and comparison with ICP-AES.
Results:
The coefficients of variation for intra-assay precision were 0.7%-1.9% for Ca, 1.5%-2.1% for IP, and 0.8%-7.4% for Zn. The recovery rates ranged from 104.1% to 104.9% for Ca, 96.3%-103.4% for IP, and 94.5%-103.2% for Zn with high, medium, and low concentrations. There were significant correlations between Ca, IP, and Zn levels determined by colorimetric assay and Ca, total P, and Zn levels determined by ICP-AES (Ca: r = 0.944, IP: r = 0.463, and Zn: r = 0.949, p < 0.001, n = 58).
Conclusion:
These results confirm the precision and accuracy of the colorimetric assay using clinical laboratory reagents for determining Ca, IP, and Zn levels in human milk. Its use may contribute to the rapid and easy provision of appropriate DHM to preterm infants.
