Simultaneous Measurement of Plasma Volume in Man With T-1824 and an Improved I¹³¹-Albumin Method

¹ From the Department of Medicine, University of Colorado School of Medicine, Denver, Colorado

Thirteen simultaneous measurements were made with T-1824 and an improved I¹³¹-albumin method in 12 subjects. Significant loss of labeled protein to glassware was prevented by addition of homologous plasma to the I¹³¹-albumin used for injection and preparation of standards and by using physiological saline containing carrier protein (2 ml plasma/100 ml) as diluent for the standards. In this series the I¹³¹-albumin dilution spaces averaged +5.3% higher than the dye dilution spaces. At the time of each measurement the proportion of loosely bound I¹³¹ was also determined by precipitating the labeled protein with trichloroacetic acid and measuring the radioactivity in the supernatant. In different samples it varied from 2.1 to 4.8% of the total. If correction is made for the loosely bound I¹³¹, a large part of which was shown to be removed quickly from the circulation, the average difference is reduced to +1.2% (S.D. 3.0%). These findings indicate that, when the above precautions are taken, the I¹³¹-albumin method gives measurements in close agreement with measurements by the dye method.