Matrix Selection for Measurement of Zinc Levels

Abstract

INTRODUCTION: Measurement of blood zinc levels is frequently used in the diagnosis of a few conditions such as growth retardation, immunodeficiency, infertility, neurological disorder, and acrodermatitis enteropathica. The serum matrix is the most preferred one to determine zinc levels due to the ease of analysis with other tests and cost-effectiveness of blood collection tubes used to obtain serum samples. In our study, we aimed to compare serum and plasma zinc test results for accurate and reliable zinc measurement in plain tubes with clot activator and gel and in heparin-free tubes, which specifically produced for trace element analysis. METHODS: Twenty-seven randomly selected patients were included in the study. Blood samples drawn simultaneously from patients were pipetted into tubes with clot activator and gel (SST) (SST II Advance, Vacutainer, Becton Dickinson and Company, USA) as well as into trace element tubes with sodium heparin (NH) (NH Trace Elements Sodium Heparin, Vacuette, Greiner Bio-One GmbH, Austria). After the centrifugation process, zinc levels in serum and plasma samples were analyzed by colorimetric method using an autoanalyzer. Bias between serum and plasma zinc levels was evaluated according to the allowable bias criterion based on biological variation and regression analysis performed. RESULTS: The mean and standard deviation of serum and plasma zinc levels were 49.0+-11.5 μg/dL and 46.4+-12.0 μg/dL, respectively, and a statistically significant difference was determined (p=0.012) in between. Besides, the bias between serum and plasma was 6.8%, which was above the allowable bias (3.3%) and considered as clinically significant. No systematic or random errors detected. DISCUSSION AND CONCLUSION: When selecting a blood collection tube for trace element analysis, the structural differences between tubes and the matrix effect should be considered carefully.

Keywords

• zinc
• plasma
• serum
• specimen collection