Point-of-care ionised calcium testing: lab validation and clinical feasibility study.

Background: Patients undergoing thyroid and parathyroid surgery require frequent assessment of blood calcium levels to guide their management, and currently such measurements are performed mostly in hospital environments on main laboratory platforms. The aim of this study was to explore the potential use of a non-medical LAQUA device designed to measure ionised calcium in environmental samples as a pocket-size point-of-care device able to measure blood calcium concentration in patients after thyroid and parathyroid surgery.

Methods: The protocol of the study consisted of three distinctive phases: surveying the technological landscape and identifying currently available devices and technologies able to measure calcium in a small volume of whole blood easily, quickly, and accurately (Phase 1); testing the potential candidate device in a laboratory (Phase 2); and performing a prospective, single-arm study (IRAS ID 236079, Protocol number 18/0058, REC ref 19/LO/1740), during which simultaneous calcium measurements were performed on venous and capillary blood on LAQUA and 'gold standard' platforms Roche Cobas-Calcium-Gen.2 and Blood Gas Analyser ABL90 (Phase 3).

Results: In Phase 1, LAQUA (HORIBA Inc. Japan) was identified as the most promising potential POC device in terms of size, simplicity of use, and cost effectiveness. In Phase 2, LAQUA showed good accuracy (Δmean = 0.09; P = 0.33) and precision (CV 3.41%) in measuring ionised calcium in standardised solutions. In Phase 3, 30 patients were recruited and had 67 sets of measurements. 'Gold standard' venous adjusted calcium (Roche) and ionised calcium (BGA) were equivalent, R = 0.95, (P < 0.001). Strong positive correlation R = 0.75 (P = <0.001) was observed between venous ionised calcium measured on BGA and LAQUA. Positive but weaker correlation was found between venous (BGA) and capillary (LAQUA) ionised calcium R = 0.68, (P = <0.001), and between venous and capillary ionised calcium (LAQUA), R = 0.56 (P = <0.001).

Conclusions: LAQUA is a promising device, which can measure ionised calcium accurately in small venous but not yet capillary blood samples. Further device development is needed before it can be recommended as a potential POC device to measure calcium in blood.