Isosthenuria refers to the excretion of urine whose specific gravity (concentration)'s neither greater (more concentrated) nor less (more dilute) than that of protein-free plasma. This's the hallmark of such disease states as chronic and acute renal failure in which the kidneys lack the ability to concentrate or dilute the urine and so the initial filtrate of the blood remains unchanged despite the need to conserve or excrete water based on the body's hydration status. Sickle-cell trait, the het… (More on Isosthenuria)