Relationship between Direct Measured and Calculated Ionized Calcium in Maintenance Hemodialysis Patients

Won, Jun Yeon; Kim, Sung Rok

Abstract

It is important to maintain normal calcium concentration especially ionized calcium concentration in chronic renal failure patients on hemodialysis. The direct measurement of ionized calcium is less commonly used due to a lack of automated equipment as well as the cost of laboratory equipment. Numerous formulas for adjusted total calcium and calculated ionized calcium are used in clinical practice. We examined the relationship between direct measured ionized calcium and total calcium, corrected total calcium, calculated ionized calcium (formula of Nordin et al) in 53 chronic renal failure patients on hemodialysis. The results were as follows; 1) In predialysis group, plasma total and ionized calcium levels were 2.36+/-0.26, 1.04+/-0.21mmol/L respectively, and higher than normal controls. The correlations between plasma ionized calcium and total calcium, calculated ionized calcium, corrected total calcium were r=0.72 (P=0.0001), r=0.81 (P=0.0001), r=0.65 (P=0.0001) respectively. The plasma ionized calcium level was not correlated with the level of albumin, pH, phosphate, parathyroid hormone. 2) The plasma total and ionized calcium levels were significantly increased with hemodialysis and values were 2.49+/-0.14mmol, 1.14+/-0.14mmol/L respectively. The correlation between ionized and total calcium was r=0.41 (P=0.0021). These results suggested that the calculated ionized calcium (formula of Nordin et al) and total calcium can be used to predict the plasma ionized calcium level in chronic renal patients on hemodialysis.