Free water clearance of -1.3 ml/min signifies: (A) No secretion of vasopressin, (B) Urine is hypotonic to plasma, (C) Urine is hypeonic to plasma, (D) Urine is isosmotic to plasma
Answer is C. In the physiology of the kidney, free water clearance (CH2O) is the volume of blood plasma that is cleared of solute-free water per unit time. If an individual is producing urine more dilute than the plasma, there is a positive value for free water clearance, meaning pure water is lost in the urine in addition to a theoretical isoosmotic filtrate. If the urine is more concentrated than the plasma, then free water is being extracted from the urine, giving a negative value for free water clearance.Ref: Ganong&;s review of medical physiology; 23rd edition; page no; 657