Why get tested?
To determine the function of your kidneys

When to get tested?
As a practical test to look for evidence of kidney damage. For a more definitive assessment of kidney function or to monitor changes in kidney function if you already have kidney disease, measurement of creatinine clearance is preferred.

Sample required?
Creatinine Clearance can be calculated using your age, weight, gender, and serum creatinine (requires a blood sample from a vein in your arm); in some formulas, race is also used in the calculation. Measured Creatinine Clearance, which gives an assessment of Glomerular Filtration Rate (GFR), is calculated from serum and urine creatinine levels and requires a blood sample from a vein in your arm and normally a 24-hour collection of urine.