medwireNews: Findings from three studies published in Diabetologia suggest that screening for type 2 diabetes at the population level is not associated with an overall decrease in mortality rates, but may reduce the risk for death and cardiovascular disease (CVD) among those with diabetes.
For two of the studies, Rebecca Simmons (University of Cambridge, UK) and colleagues analyzed data from the register-based nonrandomized ADDITION-Denmark trial, in which Danish adults aged 40–69 years with moderate-to-high diabetes risk who were registered with participating medical practices were invited to attend type 2 diabetes screening, while patients attending non-participating practices, who had not had their diabetes risk assessed, formed the control group.
In an analysis of the impact of screening at the population level, Simmons and team found that 7.7% of 153,107 participants in the screening group died from any cause over a median follow-up of 9.5 years, compared with 8.1% of 1,759,285 people in the control group, giving a nonsignificant hazard ratio (HR) of 0.99 after adjustment for age, gender, education, and chronic disease.
Similarly, there was no significant difference in the incidence of cardiovascular- or diabetes-related mortality risk between the screening and non-screening groups, and the rates of CVD events were comparable, at 11.7% versus 11.8% (adjusted HR=0.99).
The author of an accompanying commentary, Jonathan Shaw (Baker Heart and Diabetes Institute, Melbourne, Victoria, Australia), believes that these findings are “disappointing, but perhaps not surprising” because patients with diabetes detected through screening only represent a small proportion of the overall number of individuals who will die or experience a CVD event.
“Since most people with these events do not have diabetes, the capacity to influence mortality and CVD event rates at the population level would be very small, even if the early identification of diabetes through screening genuinely improved outcomes for screen-positive individuals,” Shaw explains.
In their second study of the ADDITION-Denmark data, however, Simmons et al restricted their analysis to patients with diabetes only, and found that the 13,992 patients with diabetes in the screening group had a significant 21% reduced risk for all-cause mortality compared with the 125,083 in the non-screening group, at 12.7% versus 15.8% (adjusted HR=0.79).
And those in the screening group also had a significant 16% lower risk for CVD events than individuals with clinically diagnosed diabetes (20.4 vs 22.8%; adjusted HR=0.84).
Taken together, the ADDITION-Denmark results “mirror those from trials of screening for other conditions, which have shown reductions in disease-specific mortality but not in overall mortality,” say the researchers.
In accordance with these results, the authors of the third study found that people with diabetes detected through a screening program in Sweden had lower rates of mortality and complications than those with clinically detected diabetes.
Olov Rolandsson (Umeå University, Sweden) and study co-authors found that 7.1% of 1024 patients with diabetes detected through the Västerbotten Intervention Programme – involving health examinations including diabetes screening at the age of 30, 40, 50, and 60 years – died over a median follow-up of 6.2–7.8 years, compared with 11.3% of 4506 patients with clinically detected diabetes who participated in the screening program, giving a significant HR of 1.70.
And the 4136 participants with clinically detected diabetes who did not participate in the screening program were more than twice as likely to die as those with screen-detected diabetes (HR=2.31).
Furthermore, patients with clinically detected diabetes were significantly more likely to experience CVD events, renal disease, or retinopathy than those with screen-detected diabetes, with corresponding HRs of 1.25, 1.89, and 1.38 for those with clinically detected diabetes who participated in screening and 1.77, 2.54, and 1.85 for non-participants.
“[S]creen-detected individuals appear to fare better than those with clinically detected diabetes,” summarize the researchers.
However, they note that “[h]ow much of these associations can be explained by earlier treatment because of screening rather than healthy user bias, lead time bias and length time bias warrants further investigation.”
Taking all the current evidence into account, Jonathan Shaw believes that “[t]he appropriate conclusion […] is that community screening programmes, such as those that have been established for colon and breast cancer, cannot be justified for type 2 diabetes in countries where opportunistic diabetes screening is functioning well, and management of cardiovascular risk factors is good.”
And the authors of a second commentary, David Simmons (Western Sydney University, New South Wales, Australia) and Janice Zgibor (University of South Florida, Tampa, USA) recommend: “The most efficient recommendation may be opportunistic screening, where patients already seeking care (including screening) for another condition are subsequently tested for diabetes or [impaired glucose tolerance/impaired fasting glucose]."
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