Although the benefits of metabolic intervention on the microvascular complications of diabetes mellitus remain unproven, it is generally assumed though not proven that prognosis in terms of blindness and renal failure will reflect the long-term glycemic response to therapy. Treatment goals however remain poorly defined. Costs and hazards of achieving near-normoglycemia in insulin-dependent diabetes mellitus (IDDM) are major. A multicenter trial was proposed to test the hypothesis that in IDDM two levels of mean glycemia, sufficiently separated to examine the control/complications relationship, could be maintained by the six collaborating centers, using randomized patient allocation to conventional insulin therapy (CIT) and continuous subcutaneous insulin infusion (CSII) as the alternative treatment modalities. Methods of maintaining and monitoring metabolic control and of assessing renal and retinal responses were to be applied, evaluated, and possibly improved. All clinics shared a common experimental protocol, which received ethical approval at each treatment center. Retinal assessment facilities were provided by the Fundus Photograph Reading Center at the University of Wisconsin in Madison, and at the Diabetic Retinopathy Department, Royal Postgraduate Medical School, Hammersmith, United Kingdom. The Central Biochemistry Laboratory was at the University of Newcastle, United Kingdom. Collaborators agreed on policy for recruitment, baseline assessment, and randomization of patients with IDDM, complicated by early microvascular disease. CIT took the form of the unchanged prestudy regimen; glycemic goals were set for CSII and their achievement based on inpatient and outpatient sampling of plasma glucose. Glycosylated hemoglobin was measured, retinal abnormalities recorded photographically, and urinary albumin excretion quantitated at baseline, 4, and 8 mo in all patients. As a prelude to the larger multicenter trial required to resolve definitively the question of the costs and benefits of intensified treatment of IDDM, The Kroc Collaborative Study was designed as a test of the feasibility of using currently available methodologies, of meeting the logistic problems of concerted clinical action in multiple centers, and the use of central assessments and of the capacity to sustain the operation for long enough to make a long-term clinical trial of treatment and prevention of the microvascular complications a practical possibility.

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