Estimating the delay between onset and diagnosis of type 2 diabetes from the time course of retinopathy prevalence.
OBJECTIVE
By correlating known diabetes duration with the prevalence of retinopathy, more than 10 years have been estimated to lapse between the onset and diagnosis of type 2 diabetes. Such calculations, however, assumed a linear model, included stages of retinopathy not specific to diabetes, and allowed 5 years for retinopathy to occur after the onset of diabetes. We calculated the duration of undiagnosed type 2 diabetes in outpatients screened for retinopathy in a hospital-based diabetes clinic after correcting these assumptions.


METHODS
Diabetic patients (n = 12,074; 35,545 fundus examinations) were stratified into younger onset (YO; age at onset <30 years) or older onset (OO; age at onset ≥30 years), insulin treated (IT) or not IT (NIT), and with mild/more severe diabetic retinopathy (AnyDR) or moderate/more severe diabetic retinopathy (ModDR). The best-fitting equation correlating known duration among the OO-NIT group with the prevalence of ModDR was used to extrapolate time from appearance of retinopathy to diagnosis of type 2 diabetes. Time for retinopathy to develop after diabetes was calculated from the equation correlating the duration among the YO-IT group with appearance of ModDR.


RESULTS
There were 1,719 patients in the OO-NIT group with AnyDR and 685 with ModDR and 756 in the YO-IT group with AnyDR and 385 with ModDR. A linear model showed ModDR appeared 2.66 years before diagnosis among those in the OO-NIT group. A quadratic model suggested that ModDR appeared 3.29 years after diagnosis among those in the YO-IT group. The resulting estimate was 6.05 years (2.66 + 3.29) between the onset and diagnosis of diabetes, compared with 13.36 years using standard criteria.


CONCLUSIONS
Using best-fitting models and stratifying by glucose-lowering treatment and severity of retinopathy substantially lowers the estimated duration of undiagnosed type 2 diabetes.
Diabetic Retinopathy Centre, Department of Medical Sciences, University of Turin, Turin, Italy massimo.porta@unito.it.
Massimo
M
Porta
Diabetic Retinopathy Centre, Department of Medical Sciences, University of Turin, Turin, Italy.
Giulia
G
Curletto
Diabetic Retinopathy Centre, Department of Medical Sciences, University of Turin, Turin, Italy.
Dario
D
Cipullo
Diabetic Retinopathy Centre, Department of Medical Sciences, University of Turin, Turin, Italy.
Roberta
R
Rigault de la Longrais
Diabetic Retinopathy Centre, Department of Medical Sciences, University of Turin, Turin, Italy.
Marina
M
Trento
Diabetic Retinopathy Centre, Department of Medical Sciences, University of Turin, Turin, Italy.
Pietro
P
Passera
Diabetic Retinopathy Centre, Department of Medical Sciences, University of Turin, Turin, Italy.
Anna Viola
AV
Taulaigo
Diabetic Retinopathy Centre, Department of Medical Sciences, University of Turin, Turin, Italy.
Sabrina
S
Di Miceli
Diabetic Retinopathy Centre, Department of Medical Sciences, University of Turin, Turin, Italy.
Antonella
A
Cenci
Department of Public Health and Paediatrics, University of Turin, Turin, Italy.
Paola
P
Dalmasso
Department of Public Health and Paediatrics, University of Turin, Turin, Italy.
Franco
F
Cavallo
D000328:Adult; D017668:Age of Onset; D003924:Diabetes Mellitus, Type 2 / Q000175:diagnosis* / Q000209:etiology; D003930:Diabetic Retinopathy / Q000150:complications / Q000453:epidemiology* / Q000503:physiopathology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007558:Italy / Q000453:epidemiology; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D011446:Prospective Studies; D013997:Time Factors