What does isothenuria refer to?

Isothenuria refers to the production of urine that has a specific gravity (SG) that is the same as that of plasma, often around 1.010 in many species. This indicates that the kidneys are not concentrating or diluting the urine effectively, resulting in urine with a specific gravity resembling that of the blood plasma. It is often seen in conditions where the kidneys are unable to respond to changes in hydration status or in certain diseases affecting renal function.

The other options, while they deal with aspects of urine concentration, do not accurately define isothenuria. High concentration of urine would imply a specific gravity greater than that of plasma, indicating the kidneys are effectively concentrating urine. Low concentration of urine refers to urine with a specific gravity lower than that of plasma, which occurs in conditions like diabetes insipidus or general kidney dysfunction. Urine with increased solutes suggests a higher concentration, resulting in a higher specific gravity than plasma, which is not indicative of isothenuria.