Choice of serum calcium measurement Ionised Vs Total Calcium

Choice of serum calcium measurement Ionised Vs Total Calcium Aim To find an association between measured and calculated ionized calcium.Objectives1.To compare ionized calcium measurement between Ion selective electrode method and calculated ionized calcium from measured total calcium value by Arsenazo III method.2.To identify the best sample (aerobic Vs anaerobic) for ionized calcium assay. Materials and methods For 100 randomly selected patients, fasting blood sample was collected in gel separator tube as anaerobic sample and plain test tube as aerobic sample. Both samples were centrifuged within 2 hours and Ionized calcium level was measured on the day itself by Ion selective Electrode method. Later in aerobic samples total calcium by Arzenaso III method, total protein by modified Biuret method and Albumin by BromoCresolGreen method were measured. Corrected total calcium and calculated ionized calcium were derived from measured parameters using formulae. Results In this cross sectional study, data obtained were statistically analysed using paired t test. There exist a significant difference between calculated iCa with measured iCa in anaerobic sample and in aerobic samples (p0.001). Corrected CaT show significant increase than measured CaT with (p0.05). The measured iCa value for anaerobic and aerobic samples that were measured directly by ISE show significant difference with p0.001. Conclusion In this comparison of methods study, the analytical performance of second generation ionized calcium analyzer over total calcium by Arsenazo III was studied. Direct measurement of ionized calcium by ISE show improved reliability with more accuracy and precision .Ionized calcium is a better indicator than total calcium for assessing actual calcium status of the body and the ideal sample is an anaerobic sample. Ionized calcium is the test of choice for all medical diagnostic and treatment purpose.