Korean J Nephrol.  1999 Nov;18(6):934-939.

Comparison of Free Ionized Calcium Levels by Direct Measurement and Those Calculated from Total Calcium, Albumin, and pH in Chronically Ill Patients

• Roh KH
• Min KH
• Yang SK
• Han SW
• Ryu JH
• Lee KW
• Kim HJ

Abstract

This study was aimed to assess the free calcium status with or without its direct measurement in patients on hemodialysis(HD: n=27) and malnourished ones from extrarenal diseases(MN: n=14). It was performed by the comparison of measured free calcium (Ca++m) levels by gas analyzer and calculated free calcium(Ca++c) levels based on those of total calcium (TCa), albumin, and pH with the modified algorithm invented by Moore(J Clin Invest. 49:318, 1970). Of 27 HD pts, 14(5296) had low[Ca++m] below 1.05mmol/L despite only 2(796) with low [TCa] below 2.05mmoV L, whereas 14 MN pts had similar numbers between low[Ca++m] and low[TCa]. Compared to MN pts, HD pts showed significantly lower mean levels(SE) of pH(7.37 0.01 vs. 7A4 0.01, p<0.01), higher[TCa](2.33 0.04 vs. 1.83 0.08mmol/L, p<0.01), and higher albumin (4.33 0.06 vs. 2.59 0.17mg/dL, p<0.01).However, [Ca++m] between 2 groups did not reveal any significant difference. Furtherrnore, in total 41 pts of 2 groups, no similarity was observed between the values of [Ca++ml and [Ca++c] but with their significant difference(p<0.05). Only[TCa] was significantly corre- lated with albumin level(r=0.73, p<0.01). Furthermore, multiple regression analysis between [Ca++m] and other factors including pH and albumin didn't show any correlation. In conclusion, this data suggests that relatively high prevalence of low values of physiologically important free ionized calcium in chronically ill pts, especially on maintenance HD, could be missed when predicted on total calcium level, and pH without its direct measurement.

MeSH Terms

Calcium*
Chronic Disease*
Humans
Hydrogen-Ion Concentration*
Prevalence
Calcium