Renal hyperfiltration in type 2 diabetes: effect of age-related decline in glomerular filtration rate.

Aims/hypothesis: We sought to characterise the effect of the age-related decline of GFR on hyperfiltration in type 2 diabetes and to identify clinical characteristics associated with hyperfiltration. Materials and methods: GFR was measured in 662 type 2 diabetic patients by plasma disappearance of 99 m-technetium-diethylene-triaminepenta-acetic acid. The prevalence of hyperfiltration was calculated using both an age-unadjusted GFR threshold of »130 ml min^-1 1.73 m^-2 and an age-adjusted threshold incorporating a decline of 1 ml min^-1 year^-1 after the age of 40. The hyperfiltering patients were compared with type 2 diabetic subjects who had a GFR between 90 and 130 ml min^-1 1.73 m^-2 and were matched for age, sex and disease duration to allow for identification of modifiable factors associated with hyperfiltration. Results: The prevalence of hyperfiltration was 7.4% when age-unadjusted and 16.6% when age-adjusted definitions were used. The age-unadjusted vs -adjusted prevalence rates for hyperfiltration were 50 vs 50%, 12.9 vs 23.4% and 0.3 vs 9.0% for patients aged «40 years, 40 to 65 years and »65 years, respectively. Both the age-unadjusted and -adjusted hyperfiltration groups had lower mean diastolic blood pressure and lower serum creatinine levels than the control groups. Although the age-unadjusted hyperfiltration group had larger kidneys compared to the control group, this difference was no longer significant when the age-adjusted definition was used. There were no differences in HbA₁c, mean arterial pressure, antihypertensive use, insulin therapy, dyslipidaemia, frequency of macro- or microvascular complications, BMI, urinary sodium, urea and albumin excretion between the groups. Conclusions/interpretation: Hyperfiltration was still more common among younger patients with type 2 diabetes even after adjusting for the expected age-related decline in GFR. Hyperfiltration was associated with a lower mean diastolic blood pressure independent of age. [ABSTRACT FROM AUTHOR]