eGFR

The headline kidney function number - reflects how well your kidneys filter waste. Declines with age and accelerates with metabolic disease.

What eGFR Measures

eGFR estimates the volume of blood your kidneys filter per minute, normalized for body surface area. Calculated from serum creatinine plus age, sex, and (in some equations) race. The CKD-EPI 2021 equation removed the race coefficient and is now standard.

eGFR declines naturally with age - about 1 mL/min/1.73m² per year after age 30. Persistent eGFR <60 for >3 months meets the definition of chronic kidney disease (CKD) regardless of cause.

What Affects This Biomarker

eGFR is influenced by: kidney function (the actual measurement target), age (declines with), muscle mass (high muscle = higher creatinine = lower estimated eGFR - equation may underestimate kidney function in muscular individuals - Cystatin C is better for this), hydration status (acute changes), recent meat intake (small bump in creatinine), and pharmacologic agents - NSAIDs lower; ACE inhibitors and ARBs cause initial small drop then stabilize; SGLT2 inhibitors cause early dip then preservation; metformin and many drugs require dose adjustment based on eGFR.

In the Context of Peptide Protocols

Track baseline + annually. Particularly important for users on metformin (eGFR <30 = stop), GLP-1s (mostly safe across eGFR), and any nephrotoxic compound. On long-term high-protein diets or peptide users with high lean mass, consider Cystatin C-based eGFR for more accurate estimate. Significant drops warrant nephrology workup.

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