Abstract

Objective: We assessed the effect of recruitment to a clinical trial upon HbA1c in patients with diabetes who had been screened and interviewed to determine eligibility, but whose therapy was otherwise unchanged.

Research Design and Methods: Eligible trials were selected from the global program of an insulin manufacturer. Included were studies in which patients were seen on a single screening visit, pharmaceutical therapy was not altered before randomization, and HbA1c was measured in a central laboratory at both screening and randomization. Three trials involving patients with type 1 diabetes (n= 429) and three trials with type 2 diabetes (n=611) were identified for analysis. The main outcome measure was change in HbA1c. Separate regression equations on the change in HbA1c were fitted for type 1 and type 2 diabetes, and included effects of baseline HbA1c and interval between the screening and randomization visits.

Results: HbA1c changed by −0.13% (range +0.09 to −0.26 %) in those with type 1 diabetes at a median of 28 days, and by −0.16% (range −0.14 to −0.27 %) for those with type 2 diabetes (median 14 days). The mean change in HbA1c in those with an interval ≥ 28 days was −0.24% (type 1 diabetes) and −0.23% (type 2 diabetes). The reduction was proportional to initial HbA1c, with large decreases in those with the poorest initial control, but no overall change in those at or below the 10^th percentile of HbA1c.

Conclusion: Recruitment to a clinical trial, independent of any therapeutic intervention, produces improvements in glucose control.