Serum Creatinine to Glomerular Filtration Rate (GFR) Ratio (24-hour urine collection)

Why This Test Is Done

Your doctor may order this test if they suspect kidney problems, such as chronic kidney disease, or if you have conditions like diabetes or high blood pressure that increase kidney risk. It can also be used to monitor kidney function after treatment for conditions like kidney stones or certain medications.

How the Test Works

You’ll collect all urine for 24 hours in a special container. Blood is drawn to measure serum creatinine levels. The urine and blood samples are then sent to a lab to calculate the ratio of creatinine in urine to blood.

Sample Collection Process

You’ll need to start collecting urine immediately after waking up and continue until you wake up the next morning. Empty your bladder first, then discard the first urine. Collect all urine in a container, changing the container if needed. A blood draw will be done on the same day, typically before or after urine collection.

What to Expect Before the Test

No special preparation is needed for the urine collection, but you may need to adjust your diet slightly to avoid foods high in creatinine (like red meat) if your doctor advises it. For the blood draw, avoid strenuous activity and eat a normal meal the day of testing.