Evaluation of the Randox colorimetric serum copper and zinc assays against atomic absorption spectroscopy

Validation of the Randox colorimetric assays for serum copper and zinc

BACKGROUND

Serum copper and zinc are measured to assess deficiency and toxicity. Atomic absorption spectrophotometry and mass spectrometry methods are expensive and require highly trained staff. Colorimetric assays are available from Randox which are inexpensive and can be automated. We validated serum copper and zinc colorimetric assays on the Binding Site Optilite analyser including comparison with flame atomic absorption spectrophotometry (FAAS) and inductively coupled plasma-mass spectrometry (ICP-MS).

METHODS

Accuracy, imprecision, lower limit of quantitation, and linearity were ascertained. The impact of triglycerides, bilirubin, nickel, and iron on assay performance was also investigated. Comparison of results from colorimetric analysis of patient and external quality assurance samples with those obtained by FAAS and ICP-MS was undertaken.

RESULTS

Intra-, and inter-assay imprecision was <9%. Serum copper and zinc assays were linear between 1.8-35.6 and 2.3-45.7 µmol/L, respectively. Agreement was good between colorimetry and FAAS (intercept = -0.7, slope = 1.04) and ICP-MS (intercept = 0.6, slope = 0.99) for serum copper in patients' samples. For serum zinc, agreement was poor between colorimetry and FAAS (intercept = 2.2, slope = 0.87) and ICP-MS (intercept = 1.9, slope = 0.98) in patients' samples. There was a poor concordance in assessment of hypozincaemia between colorimetry and FAAS/ICP-MS.

CONCLUSION

The Randox colorimetric assay for serum copper on the Optilite is simple to perform, has a short analysis time, and measured concentrations compare well with FAAS and ICP-MS. Due to poor agreement with FAAS and ICP-MS, colorimetry is not suitable for the measurement of serum zinc.

Zinc Status and Risk of Cardiovascular Diseases and Type 2 Diabetes Mellitus-A Systematic Review of Prospective Cohort Studies

Zinc is an essential trace element with proposed therapeutic effects in Type 2 diabetes mellitus (DM), however, the associations between zinc status and the prospective risks of cardiovascular diseases (CVD) and Type 2 DM have not been evaluated. The current systematic review aims to determine the relationships between zinc intake or plasma/serum zinc levels and prospective incidence of CVD and Type 2 DM. Fourteen papers describing prospective cohort studies were included, reporting either CVD (n = 91,708) and/or Type 2 DM (n = 334,387) outcomes. Primary analyses from four out of five studies reported no association between zinc intake and CVD events, when adjusted for multiple variables. Higher serum zinc level was associated with lower risk of CVD in three out of five studies; pronounced effects were observed in vulnerable populations, specifically those with Type 2 DM and patients referred to coronary angiography. The limited evidence available suggests no association between zinc status and Type 2 DM risk. Further investigations into the mechanisms of zinc's action on the pathogenesis of chronic diseases and additional evidence from observational studies are required to establish a recommendation for dietary zinc in relation to the prevention of CVD and Type 2 DM.