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


METHODS
GFR was measured in 662 type 2 diabetic patients by plasma disappearance of 99 m-technetium-diethylene-triamine-penta-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 HbA(1)c, 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
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.
Premaratne
E
E
Endocrinology Unit, Department of Medicine, University of Melbourne, Austin Health, Melbourne, VIC, Australia. malin@ieee.org
Macisaac
R J
RJ
Tsalamandris
C
C
Panagiotopoulos
S
S
Smith
T
T
Jerums
G
G
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging; D001794:Blood Pressure / Q000502:physiology; D015331:Cohort Studies; D003404:Creatinine / Q000097:blood; D003924:Diabetes Mellitus, Type 2 / Q000097:blood / Q000503:physiopathology*; D003928:Diabetic Nephropathies / Q000097:blood / Q000453:epidemiology / Q000503:physiopathology; D005260:Female; D005919:Glomerular Filtration Rate / Q000502:physiology*; D006801:Humans; D007668:Kidney / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D015995:Prevalence
D003404:Creatinine