Diabetic nephropathy and end-stage renal failure: the Norwegian story

Diabetic nephropathy is the most common single cause of end-stage renal failure (ESRF) in the Western world, recorded as the cause of renal failure in up to 40% to 45% of those entering renal replacement therapy (RRT) programs. However, marked differences exist between countries; the percentage of patients entering RRT in Norway because of diabetic nephropathy is 10% of the incident RRT population. The percentage in the United States is approximately 40%; therefore, the purpose of the present study was to compare data from Norway with data from the United States in an attempt to detect factors that might explain some of the differences. To make the comparisons as valid as possible, an attempt has been made to focus on populations of similar genetic make-up. The incidence of type 1 diabetes is a little higher in Norway than in the United States, whereas the prevalence of type 2 diabetes may be twice as high in the United States as in Norway; marked differences in the prevalence of obesity is probably a significant causative factor. There seems to be no striking difference in the prevalence of microalbuminuria in people with diabetes in the two populations, whereas there are insufficient data to compare the prevalence of overt proteinuria. The incidence of patients with a diagnosis of diabetic nephropathy as the cause of ESRF entering RRT in the two study populations showed marked differences; the incidence for 1997 was 8.9/million population in Norway and 113/million population in the United States. The proportion of type 2 diabetes was 46% in Norway and 64% in the US (1997). It is unlikely that the marked difference in incidence of RRT can be explained by differences in type 2 diabetes prevalence alone. The populations may not be directly comparable, and differences in the size of study populations and in the choice of renal diagnosis in patients with diabetes as a comorbid factor at the beginning of RRT may introduce uncertainties. Further, data on other factors--such as incidence of death before RRT is indicated, quality of care, and health care delivery, expressed as degree of blood pressure and metabolic control--were not available. Differences in acceptance of diabetes patients into RRT programs are not believed to contribute significantly. Norway is seeing a development toward increasing body weight and a change toward a more sedentary lifestyle, together with an increasing prevalence of type 2 diabetes earlier in life than has previously been the case. An increase in diabetic nephropathy and need for RRT because of type 2 diabetes must therefore be expected in Norway. To understand differences and to best design preventive programs, further comparative studies of the two populations seem warranted.