Serum Ionized Calcium and Corrected Total Calcium in Borderline

We studied 25 borderline-hyperparathyroidism patients whose total serum calcium concentration was within normal limits (reference range: 2.25-2.75 mmol/liter) but whose concentrations of serum ionized calcium were above normal (reference range: 1.03-1.23 mmol/liter). Their hyperparathyroidism was histopathologicalty verified. To compare the discriminating value of corrected serum calcium with ionized calcium, we studied the serum cal-cium and albumin concentrations in a reference group of 2098 patients. After patients from endocrine and dialysis departments were excluded from the reference group, we obtained the range (mean ±2 SD) 2.05-2.71 mmol/liter for uncorrected serum calcium and 2.11-2.63 mmol/liter for corrected serum calcium. The correction factor for calcium on albumin was 20 zmol/g. Even with this limit fo