Comparison study between colorimetric method and flame atomic absorption spectrophotometry in serum zinc status

Abstract

Introduction: Zinc is an essential trace element for human life and its deficiency affects human growth and development. Serum zinc concentration (SZnC) provides useful information in the clinical categorization of deficiency and toxicity states. Objectives: This paper presents a comparison study of Flame Atomic Absorption Spectrometry (FASS) and the Colorimetric method in the analysis of SZnC and hypozincemia. Methods: The serum concentrations of zinc of 93 patients (1 to 31 years old) with chronic diseases were used for analysis. Statistical analytical: for SZnC, Pearson correlation coefficient, simple linear regression analysis, Bland & Altman method (B&A), and concordance correlation coefficient (CCC) were valued; and for hypozincemia, the differences were studied and Cohen’s Kappa index was used. Results: The main results indicate the means of the SZnC by both methods presented neither significant difference (p=0.328) nor linear relation (R=0.18, p=0.077). Furthermore, the percentage of cases of hypozincemia by the Colorimetric method was almost double (13%) than by the FASS (8%). There was only one coincident case in both methods at <70 μg/dl. Discussion: The Colorimetric method in hypozincemia ranges predicted lower values with the FASS. This concordance poor between both methods was corroborated with a concordance correlation coefficient (CCC) lowly of 0.17. Moreover, the Cohen’s Kappa index (-0.013) shown a concordance poor between both methods, too. In other studies, the variability of SZnC by Colorimetric method is more than FASS. Conclusion: In summary, despite that, the mean of serum concentrations of zinc by both methods is similar; the diagnosis of cass with hypozincemia is not. The degree of agreement between methods is poor, with a poor strength of concordance to diagnosis hypozincemia. Therefore, we recommended the use of FASS to evaluated zinc status and diagnosis of hypozincemia, instead of the Colorimetric method.