In the physiology of the kidney,<unk>  <unk>  is the volume of blood plasma that is cleared of solute-free<unk>  per unit time. An example of its use is in the determination of an individual's state of hydration. Conceptually,<unk>  should be thought of relative to the production of isoosmotic urine, which would be equal to the osmolarity of the plasma. If an individual is producing urine more dilute than the plasma, there is a positive value for<unk> , meaning pure<unk>  is lost in the urine in addition to a theoretical isoosmotic filtrate. If the urine is more concentrated than the plasma, then<unk><unk>  is being extracted from the urine, giving a negative value for<unk> . A negative value is typical for<unk> , as the kidney usually produces concentrated urine except in the cases of volume overload by the individual.
Free water clearance
Net acid excretion
PAH clearance
Renal clearance ratio
Diffusing capacity
Glomerular filtration rate
Arterial input function
Renal blood flow