Final answer:
Fluid restrictions in patients receiving hemodialysis are related to the kidney's inability to concentrate or dilute urine based on fluid intake.
Step-by-step explanation:
In patients receiving hemodialysis, fluid restrictions are related to the inability of the kidneys to concentrate or dilute urine based on fluid intake. During osmolality testing, if the kidneys cannot respond appropriately to restricted fluid intake, it may indicate decreased kidney function.