Effect of Hydration Status on Plasma and Serum Volume

Hydration status is not typically controlled when obtaining hematological measures in clinical practice. This is an important consideration since hydration status may affect plasma and serum volumes and therefore the concentration of plasma‐ and serum‐based biomarkers; which would expectedly decrease with increased plasma or serum volume and increase with decreased plasma or serum volume. Although the effect of hydration status on plasma volume after exercise has been investigated, there is no published research on how hydration status affects plasma and serum volume in resting individuals who have not completed a prior bout of exercise. Objective To determine if differences in hydration status cause changes in plasma and serum volume that should be taken into consideration when measuring clinically relevant plasma‐ and serum‐based biomarkers. Methods 22 subjects (18 females/4 males) underwent control, hydration, and dehydration protocols in a counterbalanced order within a seven‐day period at the same time of day. A 12‐hour fast from food was required in both hydration and dehydration protocols. The hydration protocol required subjects to drink an ample amount of water (at least 4, 8‐ounce cups of water for females and at least 6, 8‐ounce cups of water for males) during the 12‐hour fasting period, while dehydration required fasting from any fluids. During the control protocol, subjects were allowed to continue their normal dietary routine. Hydration status was determined by spot urine osmolality, spot urine specific gravity, spot urine color, body mass, percent body water, plasma osmolality, and serum osmolality. A one‐way repeated measures ANOVA was run on all variables to determine statistical significance. Results Body mass was greater (p<0.001) after the hydration protocol (67.3 ± 13.1 kg) compared to the dehydration protocol (66.6 ± 13.0 kg). Urine color was significantly (p<0.001) lighter after the hydration (3.0 ± 1.5) compared to dehydration (6.0 ± 1.2) protocol. Urine osmolality was significantly lower (p<0.001) after the hydration protocol (394.6 ± 275.8 mosm×L −1 ) in comparison to the dehydration protocol (839.6 ± 130.3 mosm×L −1 ). Plasma osmolality was significantly lower (p<0.01) after the hydration (280.3 ± 4.4 mosm×L −1 ) compared to dehydration (285.4 ± 4.0 mosm×L −1 ) protocol. Percent body water (p=0.851), urine specific gravity (p=0.076), serum osmolality (p=0.713), plasma volume (p=0.658), and serum volume (p=0.399) all were not significantly different among protocols. Conclusion The significant difference in body mass, urine color, urine osmolality, and plasma osmolality after completion of the hydration compared to dehydration protocols indicate that these protocols successfully resulted in a respective hydrated and dehydrated status in our subjects. However, difference in hydration status did not result in concomitant changes in plasma or serum volumes. These results indicate that, in non‐exercised individuals, hydration status will likely not have an effect on clinical results obtained from plasma‐ or serum‐based biomarkers. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .