Blood tests for Alzheimer’s disease may be misleading for people with kidney problems

The study did not prove that poor kidney function directly raises levels of biomarkers for Alzheimer’s disease. I have simply identified the link between the two.

The kidneys play an essential role in removing waste and toxins from the bloodstream, and removing these substances through urine.

How kidney health shapes biomarker readings

“Our study found that when the kidneys are not working properly, there may be higher levels of biomarkers of Alzheimer’s disease in the blood,” said study author Francesca Gasparini, MD, of the Karolinska Institute in Stockholm, Sweden. “Although we did not find that reduced kidney function increased the risk of dementia, we did find that poor kidney function may accelerate the onset of dementia in people with higher levels of biomarkers. This highlights the need for clinicians to consider kidney function when interpreting results of Alzheimer’s disease biomarkers in the blood.”

The study followed 2,279 adults with an average age of 72, none of whom had dementia at the start. Each participant completed medical examinations, cognitive assessments, and blood tests that measured kidney function along with levels of several biomarkers of Alzheimer’s disease. These included tau and amyloid beta proteins, neurofilament light chain proteins, and glial fibrillary acidic proteins.

Long-term tracking of kidney function and dementia

Participants were monitored for approximately eight years. Of the 1,722 people with normal kidney function, 221 developed dementia. In a group of 557 individuals with impaired kidney function, 141 of them developed dementia.

The researchers noted that poor kidney function was associated with higher levels of most of the biomarkers of Alzheimer’s disease measured in the study. Removing participants who developed dementia during the follow-up period did not change the overall patterns.

Dementia risk, genetic factors, and biomarker levels

After adjusting for factors such as age, sex, and APOEe4 — a genetic biomarker that indicates a strong risk of developing Alzheimer’s disease — the researchers found no increased likelihood of developing dementia in people with poor kidney function compared to those with healthy kidneys.

However, the study identified a subgroup of individuals with impaired kidney function and high neurofilament light chain levels who had nearly twice the risk of developing dementia compared with people with preserved kidney function and the same high biomarker levels. Gasparini explained that this may mean that kidney health affects the timing of dementia onset in those with elevated biomarkers, even if it does not increase the risk of dementia overall.

Why is monitoring kidney function important?

“When looking at these biomarkers in older adults, monitoring kidney health may be more important than one might think,” Gasparini said. “Monitoring kidney health may help doctors better interpret these biomarkers and identify people who may be at risk of developing the disease more quickly.”

One limitation of the research is that biomarkers associated with Alzheimer’s disease were measured only once. This means that the study could not determine how changes in kidney function over time affect levels of biomarkers. In addition, most participants were highly educated and lived in urban areas in Sweden, so the results may not apply equally to other populations.