Hyperfiltration in type 1 diabetes: does it exist and does it matter for nephropathy?
OBJECTIVE
Hyperfiltration is widely regarded as a contributing factor to the development of microalbuminuria and progressive nephropathy in type 1 diabetes. However, recent studies have questioned this conclusion.


METHODS
To address this conflicting evidence, we examined the association between hyperfiltration and progression to microalbuminuria in 2,318 adults with type 1 diabetes. We also compared the estimated GFR in our diabetic patients with rates observed in 6,247 adults from the Finnish general population, using age- and sex-specific z scores.


RESULTS
The distribution of estimated GFR in adults with type 1 diabetes and normoalbuminuria was not significantly different from that expected in the general population (p = 0.51, Mann-Whitney test). Type 1 diabetic patients with a higher estimated GFR were also no more likely to develop microalbuminuria over a median of 5.2 years of follow-up than those with normal estimated GFR. This was the case regardless of whether hyperfiltration was defined by an absolute threshold, deciles of estimated GFR or a z score, using creatinine- or cystatin-based clearance formulas in men or in women.


CONCLUSIONS
Together with other studies, these data suggest that creatinine- or cystatin-based estimates of GFR do not predict the development of microalbuminuria in patients with type 1 diabetes. Moreover, in the absence of incipient or overt nephropathy, conventionally determined renal function in patients with type 1 diabetes appears no different from that in the general population. This is hardly surprising, given that these individuals, by all definitions, do not have kidney disease.
Baker IDI Heart and Diabetes Institute, PO Box 6492, Melbourne, VIC 8008, Australia. Merlin.Thomas@bakeridi.edu.au
M C
MC
Thomas
J L
JL
Moran
V
V
Harjutsalo
L
L
Thorn
J
J
Wadén
M
M
Saraheimo
N
N
Tolonen
J
J
Leiviskä
A
A
Jula
C
C
Forsblom
P H
PH
Groop
D000293:Adolescent; D000328:Adult; D000419:Albuminuria / Q000453:epidemiology / Q000209:etiology; D003922:Diabetes Mellitus, Type 1 / Q000150:complications / Q000503:physiopathology*; D003928:Diabetic Nephropathies / Q000453:epidemiology / Q000503:physiopathology*; D018450:Disease Progression; D005260:Female; D005387:Finland / Q000453:epidemiology; D005919:Glomerular Filtration Rate / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D055815:Young Adult