Diagram showing the basic physiologic mechanisms of the kidney The<unk>  or fractional excretion is a relative measure of the speed at which a constituent of urine passes through the kidneys. It is defined by following equation: : * X is the analyte substance * Cx is the<unk>  plasma<unk>  of X * Cin is the<unk>  plasma<unk>  of inulin. Creatinine is sometimes used instead of inulin as the reference substance.
Renal clearance ratio
Free water clearance
PAH clearance
Urea reduction ratio
Arterial input function
Standardized uptake value
Peak-to-trough ratio
Net acid excretion