Albumin-corrected or ionized calcium in renal failure? What to measure?

BACKGROUND

Secondary hyperparathyroidsm is frequently observed in patients with chronic renal failure, and clinical treatment guidelines have been published. Despite this, a large proportion of patients do not reach the target levels for calcium, phosphorus, calcium x phosphorus product, or intact parathyroid hormone. The use of albumin-corrected calcium is recommended as calcium measurement, but it is the concentration of ionized calcium that is biologically active. We hypothesized that in clinical practice, the use of ionized calcium rather than albumin-corrected calcium would influence the calcium classification of the individual patient.

METHODS

Blood samples from 34 patients in chronic haemodialysis were analysed for evaluation of mineral metabolism according to K/DOQI guidelines. Blood for analysis of total and ionized calcium was drawn simultaneously. As ionized calcium is pH dependent, samples were analysed at the actual pH of the individual patient.

RESULTS

For both methods, a similar number of patients were characterized as normocalcaemic. The use of albumin-corrected calcium caused one patient (3%) to be classified as hypocalcaemic, and 10 patients (26%) as hypercalcaemic whereas with ionized calcium, five (15%) and three patients (9%) were classified as hypo- and hypercalcaemic, respectively.

CONCLUSIONS

According to present guidelines, the difference in calcium classification of patients might have clinical implications for the prescription of vitamin D, and on the choice of phosphate binders.