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To investigate duration of the period between diabetes onset and its clinical diagnosis.
Two population-based groups of white patients with non-insulin-dependent diabetes
(NIDDM) in the United States and Australia were studied. Prevalence of retinopathy
and duration of diabetes subsequent to clinical diagnosis were determined for all
subjects. Weighted linear regression was used to examine the relationship between
diabetes duration and prevalence of retinopathy.
Prevalence of retinopathy at clinical diagnosis of diabetes was estimated to be 20.8%
in the U.S. and 9.9% in Australia and increased linearly with longer duration of diabetes.
By extrapolating this linear relationship to the time when retinopathy prevalence
was estimated to be zero, onset of detectable retinopathy was calculated to have occurred
approximately 4-7 yr before diagnosis of NIDDM. Because other data indicate that diabetes
may be present for 5 yr before retinopathy becomes evident, onset of NIDDM may occur
9-12 yr before its clinical diagnosis.
These findings suggest that undiagnosed NIDDM is not a benign condition. Clinically
significant morbidity is present at diagnosis and for years before diagnosis. During
this preclinical period, treatment is not being offered for diabetes or its specific
complications, despite the fact that reduction in hyperglycemia, hypertension, and
cardiovascular risk factors is believed to benefit patients. Imprecise dating of diabetes
onset also obscures investigations of the etiology of NIDDM and studies of the nature
and importance of risk factors for diabetes complications.