A double isotope method for measurement of intestinal absorption of calcium in man

Joseph A. DeGrazia*, Peter Ivanovich, Harold Fellows, Clayton Rich

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

131 Scopus citations


Calcium absorption was measured in fasting human beings after oral administration of Ca45 in a solution containing 10 to 500 mg. stable calcium and an intravenous dose of Ca47. Absorption was determined from the ratio of specific activities of the two isotopes (oral dose/intravenous dose) in calcium of urine collected more than 24 hours later. The accuracy of this calculation was confirmed by comparison with absorption calculated from recovery of the oral dose in stools (the completeness of collection being determined from recovery of simultaneously given Cr2O3 or Cr51 labeled protein and a correction for endogenous calcium being made from the fecal recovery of the intravenous dose of Ca47). In 20 tests, the average difference between the two calculations of per cent absorption was 2.2, and the coefficient of variation, 1.6. The conditions under which the double isotope procedure gives an accurate result were evaluated and the results of its use with 3 different doses of calcium given to normal subjects are reported.

Original languageEnglish (US)
Pages (from-to)822-829
Number of pages8
JournalThe Journal of laboratory and clinical medicine
Issue number5
StatePublished - Nov 1 1965

ASJC Scopus subject areas

  • Pathology and Forensic Medicine


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