Evaluation of NM-BAPTA method for plasma total calcium measurement on Cobas 8000®

A new method was developed by Roche for the measurement of plasma calcium using the chromophore 5-nitro-5'-methyl-(1,2-bis(o-aminophenoxy)ethan-N,N,N',N'-tetraacetic acid (NM-BAPTA) which could have several advantages over the CPC method. The aim of our study was to evaluate the analytical performances of the NM-BAPTA assay from Roche on c701/Cobas 8000® and to perform a comparison study of calcium values with CPC and Arsenazo III methods.

The analytical performance including imprecision study, linearity, and stability of the NM-BAPTA assay was tested on the c701/Cobas 8000®analyzer. The most frequent interferences such as magnesium and gadolinium-based contrast agents (Gd-CAs) were examined with spiked human plasma on the selected method. The calcium Arsenazo III method from Horiba (Montpellier, France) installed on ABX Pentra 400® was used as a reference method. Linear regression analysis was performed to compare data from the different methods.

The CV of the NM-BAPTA assay showed good analytical performances with CV <1.5%, in agreement with the proposed and interim European biologic goals. We found no interference neither with gadobenate dimeglumine nor with gadoteric acid considering significant findings as interference greater than 5%. In the analytical range from 0.85 to 3.80 mmol/L, the NM-BAPTA method was closely correlated to the Arsenazo III method.

Our data demonstrate that this new calcium NM-BAPTA method developed by Roche analyzers perform as well as the conventional method, especially for the outermost values. Thus, this new colorimetric assay could substitute the CPC method on Roche analyzers.