title: Whole blood versus serum ionized calcium concentrations in dialysis patients.
abstract: OBJECTIVE
  The aim of this study is to measure the difference of ionized calcium between heparinized whole blood and serum.
  
  
  METHODS
  We recruited 107 maintenance hemodialysis (HD) patients from our hospital HD unit. The clinical and laboratory data included ionized calcium in serum and in whole blood (reference, 4.07 to 5.17 mg/dL).
  
  
  RESULTS
  The level of ionized calcium in serum was higher than that in whole blood (p < 0.001). Bland-Altman analysis showed that difference for ionized calcium was 0.5027. For the difference, the nonstandardized β was -0.4389 (p < 0.001) and the intercept was 2.2418 (p < 0.001). There was a significant difference in the distribution of categories of ionized calcium level between two methods (κ, 0.279; p < 0.001).
  
  
  CONCLUSIONS
  This study demonstrates that whole blood ionized calcium is underestimated compared with serum ionized calcium. Positive difference increases as whole blood ionized calcium decreases. Therefore, significant hypocalcemia in whole blood ionized calcium should be verified by serum ionized calcium.
authors.affiliation: Division of Nephrology, Department of Internal Medicine, Yeungnam University Medical Center, Daegu, Korea.
authors.forename: Seok Hui
authors.initials: SH
authors.lastname: Kang
authors.affiliation: Division of Nephrology, Department of Internal Medicine, Yeungnam University Medical Center, Daegu, Korea.
authors.forename: Kyu Hyang
authors.initials: KH
authors.lastname: Cho
authors.affiliation: Division of Nephrology, Department of Internal Medicine, Yeungnam University Medical Center, Daegu, Korea.
authors.forename: Jong Won
authors.initials: JW
authors.lastname: Park
authors.affiliation: Division of Nephrology, Department of Internal Medicine, Yeungnam University Medical Center, Daegu, Korea.
authors.forename: Kyung Woo
authors.initials: KW
authors.lastname: Yoon
authors.affiliation: Division of Nephrology, Department of Internal Medicine, Yeungnam University Medical Center, Daegu, Korea.
authors.forename: Jun Young
authors.initials: JY
authors.lastname: Do
mesh_terms: D000368:Aged; D015415:Biomarkers / Q000097:blood; D002118:Calcium / Q000097:blood*; D005260:Female; D006801:Humans; D006934:Hypercalcemia / Q000097:blood / Q000175:diagnosis* / Q000209:etiology; D006996:Hypocalcemia / Q000097:blood / Q000175:diagnosis* / Q000209:etiology; D007674:Kidney Diseases / Q000097:blood / Q000150:complications / Q000175:diagnosis / Q000628:therapy*; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D006435:Renal Dialysis / Q000009:adverse effects; D015203:Reproducibility of Results; D013048:Specimen Handling / Q000379:methods*
chemical_list: D015415:Biomarkers; D002118:Calcium
keywords: Heparin; Hypocalcemia; Renal dialysis