EVALUTION OF RENAL FUNCTION

A. Analysis of urine

1. appearance in urine of substances not normally present; e.g., glucose, plasma proteins, hemoglobin or erythrocytes, bacteria

2. abnormal urine volume; e.g., oliguria, polyuria

3. abnormal excretion rate of substances normally present; e.g. potassium, creatinine, specific gravity (rough measure of total dissolved particles)

B. Blood plasma concentration

1. abnormal concentrations of substances normally regulated by the kidney; examples: uremia, hyperkalemia, and increased creatinine concentration of renal failure

C. Renal Clearance

1. Define: volume of blood plasma cleared of a substance by the kidneys per unit time

2. Calculation: the clearance (“C_x”) of a given substance (“x”) can be calculated from the urine (“U_x”) and plasma (“P_x”) concentrations of the substance and the urine formation rate (V) by the formula

C_x = U_x x V / P_x

3. Creatinine clearance (a endogenous substance which is filtered but neither secreted nor reabsorbed) is a useful estimate of GFR