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The Berlin Initiative Study - an epidemiological cohort study about the kidney function in the elderly

The BIS is a population-based cohort study of 2069 older adults exploring the epidemiology of chronic kidney disease (CKD) in old age. The study follows the natural course of disease and assesses associated risk factors as well as cardiovascular outcomes and death.

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The aim of the Berlin Initiative Study

The ageing process of the kidney is often associated with a loss of renal function, and there is a constant debate about whether this is a pathological loss of function or an ageing of the organs in terms of senescence.

So far, only little epidemiological data on kidney function in elderly people exists. This also applies to the question of incidences and prevalences of renal failure in old age, risk factors for the development of renal failure and the progression rate of dialysis-related renal failure.

There are several reasons for this lack of knowledge:

  • In recent decades, the topic has not had the explosive effect it has gained at once from the predicted aging of society.
  • Recruitment and care of elderly people in studies (especially studies that run over a longer period of time) is time-consuming and costly due to age-related concomitant illnesses and frailty. Therefore, older people are often excluded from studies.
  • For a long time there was a lack of a validated methodology to detect renal failure in elderly people, i. e. people >70 years of age.

The Berlin Initiative Studie (BIS) wants to close these gaps. The project consists of a two-part project:
The first part (cross-section) was used to create and validate two formulas that allow a more accurate estimation of the GFR at persons >70 years compared to conventional GFR estimation formulas.
The second part is a longitudinal study to answer questions on risk factors and progression of renal failure in old age over a period of several years. Based on the data gathered, it is possible to make statements on preventive approaches and therapies.

About the examinations

General examination

In the course of a first study round, blood pressure and pulse as well as weight and height were measured during a 40 minutes visit. Blood samples were taken for the following parameters: Red blood cell count, blood minerals, blood sugar, protein, cholesterol, lipids, thyroid, and kidney parameters. We also check urine for blood and protein.

Half of the tubes were frozen in order to determine further values such as parameters for bone metabolism. Information on lifestyle habits and risks associated with cardiovascular diseases were addressed by means of a questionnaire. All information was collected and encrypted in a pseudonymised manner in the sense of data protection. Conclusions on the person are therefore NOT possible. After the study rounds, the participants received a written report of their personal results about 2 weeks later.

Two, four and six years later, all study participants were invited to another kidney examination. In order to draw a more comprehensive picture of our study participants in the context of this age study in a holistic sense, the frailty was also recorded by means of a questionnaire as part of these follow-up examinations.

From January 2018, we will contact our study participants again, i. e. the fifth time (after a total of eight years) to find out how their health has developed in general, and of course their kidney function in particular. We would be very pleased if you would continue to participate in the Berlin Initiative Study!

Exact measurement of kidney function:

Approximately one third of all participants (600 out of 2000) were asked for an additional kidney examination to measure their kidney function exactly. These measurements did not take place at the doctors' practices but at the three Charité sites (Mitte, Wedding, Steglitz). Participation in this additional examination was of course voluntary. This examination included eight blood samples drawn from a cannula placed in a vein of your arm. These samples were drawn within an exact time frame. After the first blood sample, 5 ml of the contrast agent "Iohexol" were intravenously injected. Iohexol contains iodine and is not radioactive. In case of an allergy to iodine, people were not allowed to participate. The whole procedure ("iohexol-clearance") has been established worldwide for many years and is known to be safe. With these results we were able to measure your kidney function exactly and to compare it to the estimated results that we calculated for you. By doing so, we were able to create two new equations to estimate kidney function more exactly than current estimating equations.


The Berlin Intiative Study is member in three international consortia:

  • European CKD burden consortium
  • CKD Prognosis Consortium (CKD-PC)
  • International Network of Chronic Kidney Disease Cohort Studies (iNET CKD)
  • Global Burden of Disease Consortium (GBD)
  • European Kidney Function Consortium (EKFC)
    The EKFC brings together European research groups in the field of renal function determination. The aim is to answer common questions on renal function and its determination through regular exchange and pooling of scientific data and to make this available to the general public through publications. In addition, it is intended to provide assistance in the implementation of clinical measurement methods in day-to-day clinical practice. BIS has contributed significantly to the foundation of this consortium, which is now supported by the European Dialysis and Transplant Society (ERA-EDTA).

Funding of the BIS

The Berliner Initiative Studie is mainly financed by the KfH Foundation for Preventive Medicine, which was founded in 2005 by KfH Kuratorium für Dialyse und Nierentransplantation e. V.. The KfH Foundation for Preventive Medicine is a non-profit organisation promoting public health, welfare, science and research.

Further funding is provided by the DDnÄ - Institut für Disease Management e. V., the Dr. Werner-Jackstädt-Foundation and the Foundation for Pathobiochemistry and Molecular Diagnostics.