Kidney basics

What your kidneys do

Your kidneys clean your blood to remove waste from your body. Kidneys are made up of about a million little filtering units called nephrons. Each nephron has a filter called a glomerulus. More than one glomerulus are called glomeruli. As blood passes through the glomeruli, they filter out the waste, which gets taken out of the body through urine.

How do doctors measure kidney function?

Doctors use something called GFR, or glomerular filtration rate, to see how well your kidneys are working to filter the blood. GFR can be estimated based on the amount of creatinine—a waste product—you have in your blood. Your doctor can measure your creatinine with a blood test. One unit of GFR is equal to 1 mL/min/1.73m2.

The higher your GFR, the better your kidneys are working. Doctors use GFR to decide what stage of chronic kidney disease, or CKD, someone has.

CKD stage GFR (mL/min/1.73m2)
1 ≥90: Normal function
2 60-89: Mild reduction
3a 45-59: Mild to moderate reduction
3b 30-44: Moderate to severe reduction
4 15-29: Severe reduction
5 <15: Kidney failure

When doctors talk about “disease stages” in ADPKD, they are using these CKD stages. Stage 5, or renal failure, is also called end-stage renal disease, or ESRD.