Optimal - The Blog
February 19, 2026
The kidney function test called eGFR (estimated glomerular filtration rate) often creates confusion: patients with perfectly normal creatinine levels—meaning their kidneys are filtering waste effectively—are flagged as having suboptimal kidney function. This happens because of how eGFR is calculated.
The formula uses an inverse relationship between creatinine and eGFR (when one increases, the other decreases) and also accounts for age. So an older person with the same healthy creatinine level as a younger person will automatically have a lower eGFR—not because something is wrong, but simply because of the math.
This creates a real problem when the standard "normal" eGFR threshold is set at 90. Research shows that healthy people in their 60s have an average eGFR of 85, and those aged 70+ have an average eGFR of 75. Setting the bar at 90 means most healthy older adults get incorrectly flagged as having kidney problems.
It's important to understand that chronic kidney disease (CKD) isn't actually diagnosed until eGFR drops below 60 (and stays there for three months) or there's other evidence of kidney damage like protein in the urine. An eGFR of 82 in an older patient with normal creatinine and no other signs of damage isn't kidney disease—it's normal aging.
As a result, the optimal ODX range for eGFR has been updated to 75–160 (down from 90). This new lower threshold still catches genuinely concerning kidney function while avoiding the false alarms that come from natural, age-related decline.
The key takeaway: a single eGFR number matters less than the trend over time. A stable eGFR in the 80s is very different from one that's declining year after year, and that's what practitioners should be watching for.
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