You’ve likely seen the hype about blood tests for Alzheimer’s. A simple prick. No spinal tap required. It sounds like a miracle compared to the old way of doing things, right?
But there is a catch.
A new study in Neurology suggests your results might be skewed. Not by your brain. By your kidneys.
The Kidney Connection
The researchers followed over 2,000 adults who were free of dementia, averaging 72 years old. They checked two things. First, kidney function using eGFR (estimated glomerular filtration rate), basically measuring how well waste clears from the blood. Second, four specific Alzheimer’s biomarkers found in that same blood: tau, amyloid beta, NfL (neurofilament light chain), and GFAP.
The result was clear. Lower kidney function meant higher biomarker levels. Across the board.
The strongest link was with neurofilament light chain (NfR). This protein flags general nerve damage, not just Alzheimer’s.
When kidneys falter, waste stays in the bloodstream. Think of a clogged drain. The water isn’t flowing faster because it’s dirty; it’s standing there because it can’t get out. Elevated protein levels in blood tests might just be a sign that the filtering system is tired. Not necessarily that the brain is dying.
The backup doesn’t mean more waste is produced, just less is cleared away.
Is It Brain Damage or Just Aging?
This matters. A lot.
Even when the study removed people who later developed dementia, the link held up. So, high numbers in your blood might just be kidney trouble masquerading as brain trouble.
Here is the kicker: people with both bad kidney function and high NfL faced nearly double the risk of dementia compared to those with good kidneys but the same high biomarkers.
Impaired kidneys alone didn’t raise the risk. That is a relief, probably. Kidney decline is standard for many of us as we age.
But the context changes the meaning of the test. If your doctor orders blood work for Alzheimer’s risk, they need to factor in your kidneys. Otherwise, the numbers lie.
Does this mean the new tests are useless? No. It just means medicine isn’t simple. You can’t look at one number and diagnose the soul of the brain. You need the whole picture.
So, if you see elevated biomarkers and have some kidney wear, don’t freak out yet. It might just be your kidneys holding onto proteins they can’t process.
We still have questions to answer about what those numbers actually mean when the filters aren’t clean. And honestly?
