Evaluation of gravimetric assays of the H2O concentration in human serum and urine.
The oven-drying method and the combined freeze- and oven-drying method for gravimetrical measurement of human serum and urine H2O concentration, as well as two reported formulas for the calculation of the serum H2O concentration were evaluated. Day-to-day precision in serum and urine (coefficient of variation (CV) less than 0.95%), and recovery in serum (95-99%) were excellent. Storage at 4 degrees C and at -20 degrees C was safe at least for 3 wk and 2 mth, respectively. For the oven-drying method, which was the most practical, reference values after fasting overnight were determined (n = 47; 99% confidence interval; serum, 48.8-51.6 mol/l; urine, 51.2-53.8 mol/l). Patients in different disease categories were tested (n = 38), and had normal values mostly. Low serum values were found in a patient after hemodialysis with ultrafiltration (47.0 mol/l), and in two patients with an extreme hyperproteinemia (48.8 mol/l) and hypercholesterolemia (48.1 mol/l), respectively. Formulas for calculation of the serum H2O concentration proved unreliable. When direct measurement is impossible, a serum value of 50.5 mol/l can be substituted.
D000328:Adult; D001774:Blood Chemical Analysis; D001834:Body Water / Q000032:analysis*; D003890:Desiccation / Q000379:methods; D005260:Female; D005612:Freeze Drying; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D013048:Specimen Handling; D014556:Urine / Q000032:analysis*