Lee WH et al. – Fractional calcium absorption can be estimated by a single oral tracer method using either radioactive or stable calcium isotopes across the entire age spectrum in healthy white adult women.

• Used database of 56 observations from 26 white adult women aged 19–67 years receiving either radioactive or stable isotopes
• Reference values for fractional calcium absorption were determined from 24-h double isotopic ratios in serum and urine and from full kinetic modeling

• Equations for estimating fractional calcium absorption developed from isotopic enrichment in serum and urine from an oral tracer and measures of body size using multiple linear regression analysis
• Equations using a 4- to 6-h sample following an oral dose of either stable or radioactive isotope corrected for body size were highly correlated with reference values for fractional calcium absorption across different aged populations (r?>?0.8, p?