I’ve heard the term GFR. What does this mean?
GFR is generally accepted as the best overall index of kidney function. It is the rate that the kidney filters the blood per minute. It is the best measure of kidney function and is a rough indicator of how well your kidneys are working. Normal GFR is 90-120 mL/min (180 L/day), and is higher in men than women. The lower the GFR, the worse your kidney function. The level of GFR correlates well, albeit not perfectly, with the likelihood of developing complications of kidney disease such as CV disease, anemia, high phosphorus, and uremic symptoms.
How does the filter work?
Urine formation begins at the glomerular filtration barrier. This membrane has 3 layers. It is freely permeable to water and small dissolved solutes, but retains most of the proteins and larger particles. The main determinant of passage through this filter is molecular size.
How do I find my GFR?
You don’t find it… the blood lab does using a formula! The formula takes into account your age, weight, sex, and creatinine level. Many GP offices run this test when they send off your bloodwork for routine physicals. (All the more reason to keep up with your annual checkups!) Typical normal values for GFR in adults are 120 mL/min in men and 100 mL/min in women.
High protein diets, high salt intake, and pregnancy all increase your GFR.
Does my GFR determine if I have CKD?
A low GFR is only one finding and does not always manifest in CKD’s early stages. You can have CKD even with a normal GFR! Scary, right? Look for protein in urine or even abnormal findings on your kidney ultrasound.
GFR is not an exact science…. it’s only an ESTIMATE!
The number is not always accurate for the malnourished, obese, pregnant, amputated and/or people under 18 years old.