Association between socioeconomic status and renal function in a population of German patients with diabetic nephropathy treated at a tertiary centre

Background. Diabetic nephropathy is the most common disease leading to end-stage renal disease (ESRD) in many countries including Germany. Some previous studies, mainly from the US, suggest that low socioeconomic status (SES) may increase the risk of ESRD. No data are available whether the SES influences the development of diabetic nephropathy in patients with diabetes mellitus in Germany. Methods. This cross-sectional study was performed on patients treated at a large university outpatient department for endocrinology and metabolic diseases. A total of 174 patients with type 1 and 651 patients with type 2 diabetes and chronic preterminal diabetic nephropathy were studied [mainly chronic kidney disease (CKD) Stages 2 and 3]. Only very few CKD Stage 5 patients were included. Patients with acute kidney injury or abnormal urinary sediment were excluded. Patients were asked about their social status using a questionnaire. Social status was determined by three components: education, highest professional position achieved and household net income. Each component was assessed by a score with 1 to 7 points to generate a total score with a minimum of 3 up to maximum of 21 points. Smoking habits were also assessed by questionnaire. HbA1c, systolic and diastolic blood pressure and body mass index from the last observation were recorded. Estimated glomerular filtration rate (eGFR) was calculated according to the modified equation 7 MDRD formula. Patients were grouped into the CKD stages according to eGFR and presence of albuminuria. Multivariate analysis was used for data analysis. Results. Patients were grouped in tertiles according to their social status (Tertile 1: 307, Tertile 2: 269, Tertile 3: 269 patients). The majority of type 1 (50.9%) and type 2 (64.9%) patients were in CKD Stages 2 and 3. Multivariate analysis revealed that SES is an independent predictor of renal function in all patients as well as in type 2 diabetic patients with diabetic nephropathy. This relationship was independent of smoking behaviour, duration of diabetes and HbA1c values. There was no association between renal function and SES in type 1 diabetic patients, but a type 2 error caused by low patient number cannot be excluded. Furthermore, no significant association between SES and albuminuria (defined >= 20 mg/L) existed. There was no significant difference in the number of visits to the clinic in regard to SES excluding referral bias. Conclusions. A lower SES was associated with the presence of diabetic nephropathy in patients with type 2 diabetes in a German population. The causes for this association are likely multiple.