Body water estimation in the newborn using tritiated water.

Of all the substances used for the estimation in vivo of total body water content, the most attractive are the isotopes of hydrogen, since they enter into all the metabolic processes involving water and have no selective secretion or storage. Deuterium was the first substance used for body water estimation in vivo (Hevesy and Hofer, 1934) and is preferable to tritium because it is not radioactive; but assay of deuterium by the falling drop method is difficult and takes time to establish, and other methods, such as the mass spectrometer, require expensive apparatus. The introduction of the liquid scintillation counter has made possible the use of tritium, the radioactive isotope of hydrogen, in safe doses. Imperato, Giovannelli, Battistini, Ghirardini and Ronchetti (1960) used tritium for estimating total body water in older children, but there is no report of its use in the newborn baby. This paper describes the use of tritium in newborn children and the sources of error in the present method.