Aims: It takes years for microvascular complications in diabetes mellitus such as diabetic retinopathy (RP) and nephropathy (NP) to develop. Since retinal and renal vessels are exposed to the diabetic milieu, it is often assumed that progression of diabetic RP and NP occurs at the same time. However, smaller studies have demonstrated that this may not always be the case. The present study was undertaken to correlate diabetic retinopathy with parameters of renal function in a large ambulatory collective of patients with Types 1 and 2 diabetes.
Methods: The study design was cross-sectional. Ambulatory patients from a large university out-patient clinic were studied (323 patients with Type 1, 906 patients with Type 2 diabetes). RP status was obtained through retinal photography by an experienced ophthalmologist and was grouped into no RP, RP Stages 1-3, or blind. Retinal pathology was correlated with clinical parameters of renal function (proteinuria, estimated glomerular filtration rate according to the MDRD formula, presence of urinary sediment abnormalities, hypertension).
Results: No patient showed urinary sediment abnormalities (e.g. presence of hematuria or acanthocytes) or increased urinary excretion of immunoglobulin light chains suggesting the absence of other nondiabetic renal diseases. The majority of Type 1 diabetes patients with macroalbuminuria (> or = 200 mg/l) had some signs of RP independent of the presence of hypertension. There was a correlation between RP and microalbuminuria (r = 0.164, p < 0.01). In contrast, up to 47.5% of the hypertensive patients with Type 2 diabetes and overt proteinuria had no signs of RP. There was also discordance of microalbuminuria and RP in patients with Type 2 diabetes. Stratification according to K/DOQI States 2-5 (MDRD formula) showed that the majority of patients with Type 1 diabetes in States 3-5 had signs of RP, albeit the absolute number of patients in these K/DOQI stages was very small. In contrast, up to 40% of dialysis-dependent Type 2 diabetics (K/DOQI State 5) showed no evidence of RP.
Conclusions: This study revealed that many patients with Type 2 diabetes and renal abnormalities (proteinuria and/or renal insufficiency) showed, in contrast to Type 1 diabetics, no signs of RP. Our study was, however, limited by the lack of renal biopsies. Although urinary sediment analysis was normal in these patients, other causes for renal insufficiency (e.g. vascular nephropathy), especially in Type 2 diabetics, cannot be excluded. Nevertheless, we believe that absence of RP in patients with Type 2 diabetes does not imply that renal abnormalities including diabetic nephropathy, are also absent. It is recommended that these patients undergo renal biopsy.