Abstract
Background: Plasma or serum zinc concentration (PZC or SZC) is the primary measure of zinc status, but accurate sampling requires controlling for hemolysis to prevent leakage of zinc from erythrocytes. It is not established how much hemolysis can occur without changing PZC/SZC concentrations.Objective: This study determines a guideline for the level of hemolysis that can significantly elevate PZC/SZC.Methods: The effect of hemolysis on PZC/SZC was estimated by using standard hematologic variables and mineral content. The calculated hemolysis threshold was then compared with results from an in vitro study and a population survey. Hemolysis was assessed by hemoglobin and iron concentrations, direct spectrophotometry, and visual assessment of the plasma or serum. Zinc and iron concentrations were determined by inductively coupled plasma spectrometry.Results: A 5% increase in PZC/SZC was calculated to result from the lysis of 1.15% of the erythrocytes in whole blood, corresponding to ∼1 g hemoglobin/L added into the plasma or serum. Similarly, the addition of simulated hemolysate to control plasma in vitro caused a 5% increase in PZC when hemoglobin concentrations reached 1.18 ± 0.10 g/L. In addition, serum samples from a population nutritional survey were scored for hemolysis and analyzed for changes in SZC; samples with hemolysis in the range of 1–2.5 g hemoglobin/L showed an estimated increase in SZC of 6% compared with nonhemolyzed samples. Each approach indicated that a 5% increase in PZC/SZC occurs at ∼1 g hemoglobin/L in plasma or serum. This concentration of hemoglobin can be readily identified directly by chemical hemoglobin assays or indirectly by direct spectrophotometry or matching to a color scale.Conclusions: A threshold of 1 g hemoglobin/L is recommended for PZC/SZC measurements to avoid increases in zinc caused by hemolysis. The use of this threshold may improve zinc assessment for monitoring zinc status and nutritional interventions.
Highlights
Zinc is an essential nutrient for normal growth, healthy pregnancy, and robust immune function
The degree of hemolysis needed to increase plasma zinc concentration (PZC) and serum zinc concentration (SZC) values was calculated by using the equation [(A 3 B) O (C 3 D) O E] 3 100 = F, where A is the average PZC and SZC of the study or population, B is the measure of precision beyond which zinc values are considered increased over the mean PZC and SZC, C is the average erythrocyte zinc concentration of the study or population, D is the average erythrocyte volume of the study or population, and E is the average erythrocyte concentration of the study or population
The degree of hemolysis required to increase PZC and SZC was estimated by using values within the standard hematologic and mineral concentration reference ranges
Summary
Zinc is an essential nutrient for normal growth, healthy pregnancy, and robust immune function. To evaluate the zinc status of a population, nutritional surveys collect data on plasma zinc concentration (PZC) or serum zinc concentration (SZC) along with dietary information These studies have indicated that the prevalence of low circulating zinc is nearly twice as high as the previous estimates of zinc deficiency from dietary or stunting data alone [5,6,7]. Plasma or serum zinc concentration (PZC or SZC) is the primary measure of zinc status, but accurate sampling requires controlling for hemolysis to prevent leakage of zinc from erythrocytes. Conclusions: A threshold of 1 g hemoglobin/L is recommended for PZC/SZC measurements to avoid increases in zinc caused by hemolysis The use of this threshold may improve zinc assessment for monitoring zinc status and nutritional interventions.
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