Assessment of Renal Function by the Stable Oxygen and Hydrogen Isotopes in Human Blood Plasma

<div><p>Water (H₂O) is the most abundant and important molecule of life. Natural water contains small amount of heavy isotopes. Previously, few animal model studies have shown that the isotopic composition of body water could play important roles in physiology and pathophysiology. Here we study the stable isotopic ratios of hydrogen (δ²H) and oxygen (δ¹⁸O) in human blood plasma. The stable isotopic ratio is defined and determined by δ_sample = [(R_sample/R_STD)−1] * 1000, where R is the molar ratio of rare to abundant, for example, ¹⁸O/¹⁶O. We observe that the δ²H and the δ¹⁸O in human blood plasma are associated with the human renal functions. The water isotope ratios of the δ²H and δ¹⁸O in human blood plasma of the control subjects are comparable to those of the diabetes subjects (with healthy kidney), but are statistically higher than those of the end stage renal disease subjects (<em>p</em><0.001 for both ANOVA and Student's t-test). In addition, our data indicate the existence of the biological homeostasis of water isotopes in all subjects, except the end stage renal disease subjects under the haemodialysis treatment. Furthermore, the unexpected water contents (δ²H and δ¹⁸O) in blood plasma of body water may shed light on a novel assessment of renal functions.</p>