Measuring total blood calcium displays a low sensitivity for the diagnosis of hypercalcemia in incident renal transplant recipients.
OBJECTIVE
Hypercalcemia is a common complication in renal transplant recipients and has been associated with nephrocalcinosis and poor graft outcome. The performance of total calcium (tCa) in the diagnosis of blood calcium disturbances in renal transplant recipients is unknown.


METHODS
We compared the ability of total tCa concentration to identify low, normal, or high ionized calcium (iCa) concentration, i.e., the gold standard, in an unselected cohort of 268 renal transplant recipients. All patients were studied 3 and 12 months after successful engraftment.


RESULTS
Hypercalcemia, defined as a iCa >1.29 mmol/L, was present in 58.6 and 44.8% of the patients at months 3 and 12, respectively. tCa concentrations >10.3 mg/dl, conversely, were observed in only 13.1% of the patients. Measuring tCa had a low sensitivity (20.3 and 24.2% at months 3 and 12, respectively) for the diagnosis of hypercalcemia. The agreement (κ coefficient [95% confidence interval]) between tCa concentrations and iCa was poor (month 3: 0.11 [0.05 to 0.17]; month 12: 0.20 [0.11 to 0.30]). The risk for underestimating iCa was increased by a low total bicarbonate concentration. Metabolic acidosis was observed in 48.1 and 37.3% of the patients at months 3 and 12, respectively.


CONCLUSIONS
Total calcium greatly underestimates the diagnosis of hypercalcemia in incident renal transplant recipients. This is mainly explained by the high prevalence of metabolic acidosis in these patients.
Evenepoel
Pieter
P
Department of Medicine, Division of Nephrology, University Hospitals Leuven, Leuven, Belgium. Pieter.Evenepoel@uz.kuleuven.ac.be
Bammens
Bert
B
Claes
Kathleen
K
Kuypers
Dirk
D
Meijers
Björn K I
BK
Vanrenterghem
Yves
Y
D000138:Acidosis / Q000097:blood / Q000453:epidemiology / Q000209:etiology; D000328:Adult; D000368:Aged; D001530:Belgium / Q000453:epidemiology; D001639:Bicarbonates / Q000097:blood; D015415:Biomarkers / Q000097:blood; D002118:Calcium / Q000097:blood*; D016009:Chi-Square Distribution; D005260:Female; D006785:Hospitals, University; D006801:Humans; D006934:Hypercalcemia / Q000097:blood / Q000175:diagnosis* / Q000453:epidemiology / Q000209:etiology; D015994:Incidence; D016030:Kidney Transplantation / Q000009:adverse effects*; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D015995:Prevalence; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D013997:Time Factors; D015854:Up-Regulation
D001639:Bicarbonates; D015415:Biomarkers; D002118:Calcium