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

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.