A simple, inexpensive method of determining total body water using a tracer dose of D2O and infrared absorption of biological fluids

Abstract

An improved infrared spectrophotometric method using tracer doses of D₂O for determination of total body water (TBW) is described. Evaluation of sample preparation procedures showed that only vacuum sublimation yielded acceptable recoveries of D₂O standards in the range of 0.01–0.30 mg/ml in urine and plasma (101 ± 2.5 and 99.6 ± 2.6%, mean ± SD, respectively). Oral administration of a 10 g dose of D₂O was shown to equilibrate within 2 hr in the saliva and plasma of 10 healthy men and women, including obese (30% body fat) subjects. Calculated TBW was 39.1 ± 6.4 L which represented 74 ± 1.6% of the fat free mass determined by hydrodensitometry. The precision of the described infrared method was 2.5%. Based upon the observed sensitivity of this method, it would be possible to administer smaller oral D₂O doses, 5–6 g, and obtain reliable TBW values. The practical advantages of this method are low cost and a simple analysis that permits repeated TBW measurements over brief periods without an undue buildup of background deuterium levels in the body.