eGFR Explained: The Kidney Filter Number
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[Glossary · How doses act in the body]

eGFR (estimated glomerular filtration rate)

Also called eGFR, GFR, estimated GFR, glomerular filtration rate · Reviewed

Definition: eGFR (estimated glomerular filtration rate) is a number that estimates how well your kidneys filter waste from the blood. It is usually calculated from a blood creatinine level using a formula that includes age and sex. MedlinePlus says eGFR can also be calculated from cystatin C, a protein less affected by muscle size.

Reading the number

Results are shown in mL/min/1.73 m², the unit the Mounjaro label uses. Sources draw the lines a little differently. NIDDK says a GFR of 60 or more is in the normal range, below 60 may mean kidney disease, and 15 or less is kidney failure. The National Kidney Foundation says eGFR falls with age even without kidney disease.

MedlinePlus says eGFR is not a perfect test and an abnormal result is possible without kidney damage. Your clinician reads it with urine albumin and other results.

Why it shows up when you track doses

The Ozempic and Mounjaro labels warn about acute kidney injury from fluid loss, and say to monitor kidney function in people who report side effects that could dehydrate them, such as vomiting or diarrhea. Both labels say no dose change is recommended for kidney impairment.

Common mix-ups

  • Muscle mass. Creatinine comes from muscle wear and tear. MedlinePlus says providers may use cystatin C instead in people with a lot of muscle mass.
  • Meat before the test. MedlinePlus says some foods like meat can affect eGFR, so you may be asked to avoid them for several hours first.
  • Other factors. The National Kidney Foundation lists pregnancy, age over 70, unusual muscle mass, cirrhosis and some medicines as things that can affect eGFR.

Read more on Dose Track: Semaglutide guide · Tirzepatide guide · Logging lab results in Dose Track

General education drawn from labels and published studies, not personal medical advice. Your prescriber, pharmacist and the label that came with your product are the final word.
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Frequently asked questions

Can lifting weights lower my eGFR?+
Creatinine-based eGFR can read lower in people with a lot of muscle, because creatinine comes from muscle. MedlinePlus says providers may use cystatin C instead in that case.
Do GLP-1 drugs affect the kidneys?+
The Ozempic and Mounjaro labels warn about acute kidney injury from fluid loss and say to monitor kidney function in people with side effects such as vomiting or diarrhea.

Sources

  1. MedlinePlus (NIH): Estimated Glomerular Filtration Rate (eGFR) and GFR Tests
  2. NIDDK (NIH): Chronic Kidney Disease Tests and Diagnosis
  3. National Kidney Foundation: Estimated Glomerular Filtration Rate (eGFR)
  4. Ozempic (semaglutide) US prescribing information, sections 5, 8.6 and 14, DailyMed
  5. Mounjaro (tirzepatide) US prescribing information, sections 5, 8.6 and 14, DailyMed

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