What your eGFR number actually means
Dr. Joan J. Morales Lappot, MD5 min read · Leer en español
If you've been told your "kidney function is low," the number behind that statement is usually your eGFR. Here's what it measures, what can throw it off, and why I care more about the trend than any single result.
What eGFR measures
eGFR stands for estimated glomerular filtration rate — roughly, how many milliliters of blood your kidneys clean each minute. It's calculated from a blood test for creatinine (a waste product from muscle), along with your age and sex. Sometimes a second blood test, cystatin C, is added to make the estimate more accurate.
One number isn't the whole story
Chronic kidney disease is diagnosed only when changes last three months or longer. A single low result can come from things that have nothing to do with lasting damage:
- Being dehydrated on the day of the test
- A large meat meal or heavy exercise shortly before
- Very high or very low muscle mass
- Certain medicines that affect creatinine
Questions to bring to your visit
- What stage am I in, and has it changed?
- What did my urine albumin test show?
- Are any of my medicines hard on my kidneys?
- Is there a medicine that could slow kidney disease for me?
See the full stage chart on the Kidney Health 101 page.