MEASUREMENT OF BLOOD-VOLUME WITH AN ENRICHED STABLE-ISOTOPE OF CHROMIUM (CR-53) AND ISOTOPE-DILUTION BY COMBINED GAS-CHROMATOGRAPHY MASS-SPECTROMETRY

We used an established isotope dilution gas chromatography-mass spectr ometry method to measure blood volumes with an enriched stable isotope of chromium. The results were compared with those of the conventional method, which involves radioactive Cr-51. The two methods were compar ed simultaneously in two male subjects of different sizes, and essenti ally identical volumes were obtained. The isotope dilution method is i nsensitive to contamination with natural (unenriched) chromium and can be used to measure all of the stable isotopes of chromium. The method has potential applications in simultaneous erythrocyte survival studi es. The absence of radioactivity makes possible an accurate means of s tudying blood volume changes in children and during pregnancy.