Calcium Determination in EDTA Treated Plasma by Colorimetric Method and Microplate Reading Format

Calcium has different functions in metabolic processes and increase or decrease of calcium level in blood may lead to different disorders. Therefore, measurement of calcium level in blood is an important clinical issue. It is not possible to measure calcium in plasma samples which contain calcium chelators and we need serum samples to do so. This research aims to investigate the simple and direct colorimetric method for calcium measuring in EDTA treated plasma. In this experimental study, through adding a patented solution to EDTA treated plasma, calcium ions are released from calcium chelators and then reacted with Ortho Cresolphthalein Complexone (o-CPC) as a coloring reagent and finally product of calcium reaction is measured using microplate reading format. The details of methodology are patented on 29.04.2012 in State Organization for Registration of Deeds and Properties with registration number of 74804, and are the exclusive property for the owners. Sensitivity, precision, accuracy, and the correlation of plasma calcium with serum calcium level were investigated. Sensitivity of this method was 0.4 mg/dL. Coefficient of variation for intra assays and inter assay were less than 5% and 6% respectively. According to recovery and parallelism tests, ratio and recovery percent ranged from 90 to 110% and correlation coefficient in compare with determination of calcium in serum by the same reagent was 0.92. This method is capable of measuring calcium in EDTA treated plasma and in addition, it has the required sensitivity, precision and accuracy for common clinical tests.