Joint press release with Medical Center of University Freiburg
The German National Cohort (NAKO) reveals a noteworthy number of potentially undiagnosed kidney diseases / One in six participants showed abnormal values without a diagnosis / Early treatment could prevent or delay severe disease progression
Chronic kidney diseases usually begin without noticeable symptoms. A recent analysis from the NAKO study indicates a potentially high number of undiagnosed cases within the population in Germany. Researchers at the Medical Center – University of Freiburg analyzed urine samples from around 35,000 individuals. One in six participants showed noticable kidney values outside the reference range, yet only around four percent of participants with abnormal findings reported having received a corresponding diagnosis from a physician. In addition, blood samples from around 195,000 adults were evaluated. Here, too, the results suggested that many individuals may have impaired kidney function. The findings were published in Deutsches Ärzteblatt International on 26.06.2026.
“We found that a considerable proportion of participants showed indications of kidney disease, often without 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.”
Majority reported no diagnosis despite kidney values outside the reference range
Blood tests within the NAKO study revealed abnormalities in kidney function in around 5,000 of the 195,000 participants. Only 875 of these individuals reported having received of a corresponding medical diagnosis.
In a subgroup that underwent urine testing, the gap was even more pronounced: 6,213 out of 35,461 participants had one or more values indicating impaired kidney function or kidney damage. This corresponds to 17.5 percent of all participants, approximately one in six. Only around four percent of these individuals reported a corresponding diagnosis.
“Blood and urine values capture different aspects of kidney health. They therefore complement each other well in assessing kidney health,” says first author Dr. Peggy Sekula, statistician at the Institute of Epidemiology and Prevention at the Medical Center – University of Freiburg.
Health Risks for Patients
Undetected kidney diseases can progress and lead to severe, in some cases life-threatening, complications. Early diagnosis and modern therapies could prevent or delay such disease progression. In the long term, improved early detection could also influence the need for kidney replacement therapies such as dialysis or transplantation. However, the current analysis did not investigate this aspect.
“This study highlights an important shortcoming in the field of kidney health,” says Prof. Dr. Jan Halbritter, recently appointed Medical Director of the Department of Internal Medicine IV, Division of Nephrology at the Medical Center – University of Freiburg, who was not personally involved in the study. “Every day in the clinic, 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 prevent further loss of kidney function.”
Why this gap arises
The analysis offers several explanations for the gap between kidney values outside the reference range and diagnosed kidney disease. One thing is clear: a single such measurement is not sufficient for establishing a diagnosis. Values outside the reference range must be confirmed through additional testing.
However, initial findings are sometimes not followed up consistently enough or communicated clearly. “The results do not argue against diagnostics themselves, but rather indicate that there is still room for improvement in confirming diagnoses, follow-up, and communication regarding kidney diseases,” says Köttgen.
The analyses are based on the German National Cohort (NAKO), the largest population-based study in Germany. The researchers evaluated blood values reflecting kidney function (glomerular filtration rate) as well as urine values indicating kidney damage (albuminuria). Methodologically, this was a cross-sectional analysis without repeated measurements. Therefore, no definitive diagnosis can be derived from the data. However, previous studies have shown that initial findings outside the reference range are frequently confirmed.