10 years of the BIS: Insights into kidney function in the very elderly
For ten years, researchers from Charité – Universitätsmedizin Berlin have been studying how kidney function changes with age. Their work as part of the Berlin Initiative Study (BIS) has produced two equations which enable physicians to better estimate kidney function in elderly patients. More precise estimates of kidney function can ensure patients do not receive drugs at too high a dose. The researchers’ findings also revealed that lowering blood pressure is associated with an increased risk of death in certain elderly adults.
It is a long-established fact that kidney function decreases with age. But what level of kidney function is normal in elderly adults and how many of them have impaired kidney function? Also, how quickly does kidney function decline? The answers to these questions are of particular significance to people who need to take medications because a decline in the rate at which the kidneys eliminate a particular drug from the body may result in overdose – with potentially serious consequences. For this reason, physicians will obtain an estimate of kidney function prior to setting treatment doses for certain drugs. The problem they had previously faced was that the only equations available to estimate kidney function had been developed based on the data of younger people.
In 2009, a team of researchers led by Prof. Dr. Elke Schäffner, Deputy Director of Charité's Institute of Public Health, launched the Berlin Initiative Study to improve our understanding of kidney function in elderly adults. The aim of the research was to study more than 2,000 individuals aged 70 years or older from the Berlin and Brandenburg areas. Participants were followed up for a period of several years, undergoing detailed examinations at regular intervals. “Given that participants had an average age of 80 and presented with age-related comorbidities including, in many cases, frailty, this was no simple task,” emphasizes Prof. Schäffner.
Participants underwent five separate examinations, scheduled at two-year intervals. During these examinations, researchers asked the participants about their habits, illnesses and medications. They also measured their blood pressure and kidney function and analyzed both blood and urine samples. As it turns out, the effort was worth it: the researchers produced a veritable treasure trove of data on the health and habits of elderly adults – as vast as it is unique. One in five participants reported consuming alcohol daily. Half of all participants were either smokers or ex-smokers. One in four participants were overweight and one in four had cancer and/or diabetes. Furthermore, nearly 80 percent of participants were taking blood pressure-lowering drugs. This group of patients became the focus of an investigation into the effects of blood pressure on overall mortality. An analysis of the researchers’ data showed that it is not always beneficial for older adults to keep their blood pressure below 140/90 mmHg. The reality is, in fact, quite the opposite: lower blood pressure is associated with an increased risk of death in adults over the age of 80, and in adults who have previously had a heart attack or stroke.
The researchers also collected new data on kidney function as represented by the ‘glomerular filtration rate’. Their findings revealed that approximately half of all participants had renal impairment. The researchers also found that the equations previously used to estimate a person’s glomerular filtration rate overestimated kidney function in elderly patients. “What this means is that inaccurate estimates might result in physicians setting treatment doses which are too high for patients,” explains Prof. Schäffner, who is both a nephrologist and an epidemiologist. To remedy this situation, Prof. Schäffner worked alongside her team to develop a new method for estimating kidney function. First developed in 2012 and consisting of two formulas (known as the BIS1 and BIS2 equations), this method produces more accurate estimates of kidney function in adults aged 70 years and over. “Today, physicians can use these equations free of charge via an online GFR calculator. There are also a number of laboratory networks which have adopted this new method as part of their portfolio of tests,” says Prof. Schäffner.
Expressing her delight at the wealth of data produced by the study, she adds: “The Berlin Initiative Study has helped us to improve our understanding of health in older people and pay more attention to this age group.” Prof. Schäffner and her team are in the process of conducting further statistical analyses. They are hoping to find out how age-related kidney decline develops over time and what factors have an influence on this development.
Prof. Dr. Elke Schäffner
Deputy Director of the Institute of Public Health
Charité – Universitätsmedizin Berlin
t: +49 30 450 553 131
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