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

Nutrition Journal

Table 2 Relationship between gold-standard and new methods of measuring fractional intestinal calcium absorption in cohort 1

New method	FCA^a	Correlation coefficient (p-value)	Bias^b (p-value)	Linear regression formula	R²	Bias^b (p-value)	RMSPE^c
1 h Serum	0.14 ± 0.06	0.57 (0.008)	0.055 (<0.001)	Value x 0.5942 + 0.1119 = FCA	0.29	0 (0.999)	0.052
3 h Serum	0.20 ± 0.09	0.72 (<0.001)	-0.003 (0.805)	Value x 0.577 + 0.081 = FCA	0.58	0 (0.997)	0.040
5 h Serum	0.18 ± 0.07	0.65 (0.002)	0.012 (0.386)	Value x 0.541 + 0.096 = FCA	0.36	0 (0.997)	0.050

^a“FCA” denotes fractional calcium absorption. Data are summarized using the mean ± SD. All new methods are compared to the 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 0.20 ± 0.06 in Cohort 1 (n = 20)
^bBias was assessed using the Bland-Altman method, first reported for the raw data versus the referent values (column 4) and later reported for the derived formula versus the referent (column 7). 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
^c“RMSPE” indicates the root mean square prediction error

ISSN: 1475-2891