[Epidemiology of Chronic Kidney Disease - Ever More Patients?]

Chronic kidney disease (CKD) is a common disorder that often occurs as a complication of other common diseases such as diabetes, obesity, hypertension, or heart failure. Here we review the methodological pitfalls both in measuring kidney function and in determining the epidemiology of kidney disease. CKD is defined as the coincidence of three criteria: A reduced glomerular filtration rate, an anatomical lesion, and a duration of more than three months. Glomerular filtration rate declines with increasing age, but this alone does not constitute kidney disease. In epidemiological studies, exact measurement of glomerular filtration rate is often not feasible. Estimates of glomerular filtration rate depend on serum levels of creatinine or cystatin C, both of which are influenced by extrarenal factors. Anatomical lesion and duration of disease are almost never ascertained in epidemiological studies. Somewhat surprisingly, large-scale statistical modeling by the Global Burden of Disease Study suggests a decline in the world-wide prevalence of CKD in the past decades. In Germany, no longitudinal data is available for lack of a national register. Cross-sectional investigations report prevalences between 6 and 26 percent, depending on age, comorbidities, and geographical region. In the future, better control of risk factors may precede a decline in the incidence of CKD, with prevalences remaining stable due to better medical care and improved survival. In the long run, there is reason to believe that there will not be ever more patients with CKD.