Can serum isotope levels accurately measure intestinal calcium absorption compared to gold-standard methods?

Nutrition Journal

Table 3 Assessment of Alternative Methods to Estimate Fractional Calcium Absorption in Cohort 2

New Method^a	FCA^b	Bias^c (p-value)	Linear Regression Equation	Correlation Coefficient, Calculated vs. Referent (p-value)	RMSPE^d	Correlation Coefficient, Calculated vs. Referent^e (p-value)	Bias^{c, e} (p-value)	RMSPE^{a, d, e}
3-h Serum	0.21 ± 0.04	0.009 (0.767)	Value x 0.577 + 0.081 = FCA	0.03 (0.932)	0.074	0.47 (0.233)	0.043 (0.015)	0.039
3-h Serum & GFR	0.21 ± 0.05	N/A	Value x 0.585 + 0.001 x GFR + 0.031 = FCA	0.02 (0.966)	0.071	0.45 (0.260)	0.047 (0.007)	0.037

^aThe two best methods identified in Cohort 1 were validated in Cohort 2
^b“FCA” denotes intestinal fractional calcium absorption. Data are summarized using the mean ± SD. All new methods are compared to referent method of measuring intestinal calcium absorption based on the dose-corrected ratio of dual stable isotopes in a 24-h urine collection, which equaled 0.23 ± 0.07 in Cohort 2 (n = 9)
^cBias was assessed using the Bland-Altman method, first reported for the raw data versus the referent values (column 3) and then reported for the derived formula minus one outlier (column 8). A Bland-Altman test p-value >0.05 indicates that there is no significant difference between paired values using the gold-standard and the new method of measuring FCA
^d“RMSPE” indicates the root mean square prediction error
^eData without one outlier who had low FCA (12 %)

ISSN: 1475-2891