Updated total calcium reference intervals for Abbott Alinity c using Calcium2 reagents

A new formulation of total calcium reagents (Calcium2) for the Abbott Alinity c prompted re-evaluation of reference intervals (RI). Despite ongoing standardization efforts, differences in reagents and analytical platforms can introduce systematic bias.

Direct and indirect approaches were used to evaluate calcium RI for both a legacy formulation of calcium (CaOLD) and the new calcium2 reagents (CaNEW) on the Abbott Alinity c. The indirect method involved a large real-world dataset comprising 97,452 CaOLD results and 106,728 CaNEW results obtained from the University Health Network. Standardized preprocessing included consideration for risk wards, exclusion of patients with more than one result, abnormal albumin levels, and individuals outside of 18-110 years of age. The indirect methods used were refineR, TML, and RefLim. The direct method by non-parametric estimation involved 173 subjects with normal ionized calcium and albumin levels. RI were subsequently verified using an additional 34 healthy volunteers.

Across indirect methods, similar plasma RI were obtained for a given formulation when only patients with a single result, excluded from risk wards and with normal albumin were considered. The approach by refineR provided 2.10-2.48 mmol/L (CaNEW) vs. 2.16-2.55 mmol/L (CaOLD), whereas the RefLim method provided 2.10-2.47 mmol/L (CaNEW) vs. 2.15-2.54 (CaOLD) and TML provided 2.11-2.48 mmol/L (CaNEW) vs. 2.17-2.55 mmol/L (CaOLD). The non-parametric method produced RI of 2.05-2.50 mmol/L(CaNEW) and 2.06-2.52 mmol/L (CaOLD).

The RI for plasma total calcium on the Abbott Alinity c with CaNEW is lower than previously established.