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.
Gøransson
Lasse G
LG
Stavanger University Hospital, PO Box 8100, 4068 Stavanger, Norway. gola@sir.no
Skadberg
Øyvind
Ø
Bergrem
Harald
H
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001774:Blood Chemical Analysis / Q000379:methods / Q000592:standards / Q000706:statistics & numerical data; D002118:Calcium / Q000097:blood*; D005260:Female; D006801:Humans; D006934:Hypercalcemia / Q000097:blood / Q000175:diagnosis; D006962:Hyperparathyroidism, Secondary / Q000097:blood / Q000175:diagnosis / Q000209:etiology; D006996:Hypocalcemia / Q000097:blood / Q000175:diagnosis; D007676:Kidney Failure, Chronic / Q000097:blood* / Q000150:complications; D008297:Male; D008875:Middle Aged; D017410:Practice Guidelines as Topic; D012016:Reference Values; D012709:Serum Albumin / Q000378:metabolism
D012709:Serum Albumin; D002118:Calcium