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NAKO Health Study Reveals Underreported Cases of Possible Kidney Disease / One in six people with abnormal test results remain undiagnosed / Early treatment could prevent or delay severe complications

Chronic kidney disease usually begins without noticeable symptoms. A recent analysis of the NAKO study suggests there may be a high number of undiagnosed cases in the German population. Researchers at the Medical Center – University of Freiburg analyzed urine samples from approximately 35,000 people. One in six had abnormal kidney test results, but only about 4 percent of participants with abnormal findings reported having a corresponding diagnosis. Blood samples from approximately 195,000 adults were also analyzed. Here, too, the results indicated that many people may have impaired kidney function. The findings were published on June 26, 2026, in the *Deutsches Ärzteblatt International*.

“We found that a significant proportion of the participants showed signs of kidney disease—often without the individuals themselves being aware of it,” says Prof. Dr. Anna Köttgen, director of the Institute of Epidemiology and Prevention at the Medical Center – University of Freiburg. “This could point to shortcomings in early detection or in communication between patients and physicians.”

Most Reported No Diagnosis Despite Abnormal Kidney Values

Blood tests conducted as part of the NAKO study revealed abnormalities in kidney function in approximately 5,000 of the 195,000 participants. Only 875 of these individuals reported being aware of a corresponding medical diagnosis. 

In a subgroup that underwent urine tests, the gap was even more pronounced: 6,213 out of 35,461 participants had one or more abnormal values for kidney function or kidney damage. This corresponds to 17.5 percent of all participants—roughly one in six. Only about four percent of these individuals reported having received a corresponding diagnosis.

“Blood and urine test results capture different aspects of kidney health. That’s why they complement each other well when it comes to assessing kidney health,” said lead author Dr. Peggy Sekula,a statistician at the Institute of Epidemiology and Prevention at the Medical Center – University of Freiburg.

Health Risks for Patients 

Undiagnosed kidney disease can progress and lead to severe, sometimes life-threatening complications. Early diagnosis and modern therapies could prevent or delay such complications. In the long term, improved early detection could also influence the need for renal replacement therapies such as dialysis or transplantation. However, the current analysis did not examine this.

“The study sheds important light on a problematic situation in the field of kidney health,” says Prof. Dr. Jan Halbritter, who recently became Medical Director of the Department of Medicine IV with a focus on nephrology at the Medical Center – University of Freiburg and who was not personally involved in the study. “Every day at the hospital, we see the damage caused by kidney diseases that are detected too late. It is crucial to identify the underlying cause as early as possible in order to provide targeted treatment and halt the loss of kidney function.” 

Why the Gap Exists

The analysis offers various explanations for the gap between abnormal kidney test results and diagnosed kidney disease. One thing is clear: a single measurement is not sufficient for a diagnosis. Abnormal results must be confirmed with further tests. 

However, initial findings are sometimes not followed up on consistently enough or communicated clearly. “The results do not call into question the diagnostic process itself, but rather indicate that there is still room for improvement in confirming diagnoses, follow-up, and communication regarding kidney disease,” says Köttgen.

The analyses are based on the NAKO Health Study, the largest population-based study in Germany. The study evaluated blood tests for kidney function (glomerular filtration rate) as well as urine tests for kidney damage (albuminuria). Methodologically, this is a cross-sectional analysis without repeat measurements. A definitive diagnosis cannot be derived from it. However, previous studies show that abnormal findings are often confirmed.

Original title: Glomerular filtration rate, albuminuria, and reported kidney disease in comparison: Results from the German National Cohort (NAKO)
DOI: 10.3238/arztebl.m2026.0053
Link to the study: https://api.aerzteblatt.de/pdf/123/13/m345.pdf