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Objective Calcium absorption is an important determinant of calcium retention and bone metabolism. However, most methods of measuring calcium absorption, including the well-established dual stable isotope method, are costly and cumbersome to implement. We evaluated whether an oral calcium tolerance test (OCTT), which involves measuring calcium excretion in a fasting 2-h urine collection and two 2-h collections following an oral calcium dose, may be a useful index of calcium absorption in older adults consuming a fixed calcium intake of 30 mmol/day. Design After a 10-day metabolic diet containing 30 mmol/day of calcium, subjects had calcium absorption measured using the dual stable isotope method and the OCTT. Participants Eleven healthy subjects aged 54–74 years. Measurements Fractional calcium absorption (FCA), calcium excretion in a fasting 2-h urine collection and two 2-h collections in response to a 10-mmol calcium dose (total intake 30 mmol/day). Results Calcium excretion from several combinations of the urine collections was examined in relation to FCA. The most predictive of FCA was calcium excretion 4 h following the calcium dose. This measure was significantly correlated with FCA ( r = 0·735, P = 0·010), fitting 54% of the variability in FCA. Conclusion Urinary calcium excretion during the 4 h after a 10-mmol calcium dose is a useful index of calcium absorption among older adults consuming recommended calcium intakes. This test is inexpensive, easy to implement and potentially useful in large clinical studies. [ABSTRACT FROM AUTHOR]