Evidence that even “normal” albuminuria may denote incipient GFR reduction in patients with type 2 diabetes mellitus

AimsIn patients with diabetes and microalbuminuria, small changes of GFR could have been missed, due to the lack of sensitive methodology for GFR determination in clinical practice (creatinine based calculations). Therefore we explored the relation of the degree of albumin excretion with Cystatin C, which has been recently proved to be a better marker of GFR, compared to serum creatinine.MethodsWe studied 179 patients with type 2 diabetes, in whom renal function and microalbuminuria were evaluated.ResultsIn patients with normal renal function, GFR/MDRD ≥ 60 ml/min/1.73 m2, (n = 79), urinary albumin concentration (UAC) was significantly correlated with Cystatin C, both in patients with normoalbuminuria (r = 0.547, p < 0.023) or microalbuminuria (r = 0.305, p < 0.035), while it was not correlated either with serum creatinine or calculated creatinine clearance. In patients with GFR/MDRD < 60 ml/min/1.73 m2, (n = 100), UAC was significantly correlated with Cystatin C, also both in patients with normoalbuminuria (r = 0.536, p < 0.032) or microalbuminuria (r = 0.340, p < 0.016), while it was significantly correlated with serum creatinine and calculated creatinine clearance only in those with microalbuminuria.ConclusionsSubtle changes in renal function, as judged by Cystatin C concentration, may parallel the degree of albuminuria, even in the normoalbuminuric stage. This finding needs further confirmation by more appropriate methodology in prospective follow up studies.