Screening for type 2 diabetes mellitus

Review question

What are the health effects of screening compared to not screening for type 2 diabetes mellitus?

Background

Type 2 diabetes mellitus is a metabolic disorder characterised by high blood sugar which can lead to complications like kidney and eye disease. It can develop at any age but usually peaks in adults 65 years of age and above and may be treated in the beginning through diet and exercise. Type 2 diabetes mellitus may have no or few symptoms at the start and thus may go undiagnosed. Screening of apparently healthy people could lead to early detection and treatment of type 2 diabetes mellitus as well as prevent or delay the development of related complications.

Study characteristics

We found one randomised controlled trial (a clinical study in which participants are assigned to one of two or more treatment groups using a random method) where 20,184 high-risk individuals from 33 general practices in Eastern England were either invited or not invited to screening for type 2 diabetes (the ADDITION-Cambridge study). Eligible participants had to have an elevated diabetes risk score but no known diabetes. The diabetes risk score to identify high-risk individuals comprised variables relating to age, sex, body mass index, and the use of prescribed steroids and anti-hypertensive medication. Practices were eligible to participate if they could provide data for calculation of the risk score for at least 70% of their patients. A total of 11,737 participants attended screening in actuality, and 4137 participants represented the no-screening group. In both groups, 36% of participants were women; the average age of participants was 58.2 years in the screening group and 57.9 years in the no-screening group. Almost half of participants in both groups were on medication for high blood pressure.

This evidence is up-to-date as of May 2019.

Key results

We are uncertain about the effects on screening for type 2 diabetes mellitus on death from any cause and death from diabetes-related causes (the only outcomes of importance for our review for which study authors provided reliable data). The included study did not report on side effects of screening, new cases of type 2 diabetes, health-related quality of life, glycosylated haemoglobin A1c (HbA1c) as a long-term measurement of glucose control, and socioeconomic effects (such as costs of screening, use of medication, number of consultations).

Certainty of the evidence

We based the certainty of the evidence on only one study. The overall certainty of the results from this study is low, because the results are not precise, that is they could change in any direction if new studies are published.

Authors' conclusions: 

We are uncertain about the effects of screening for type 2 diabetes on all-cause mortality and diabetes-related mortality. Evidence was available from one study only. We are therefore unable to draw any firm conclusions relating to the health outcomes of early type 2 diabetes mellitus screening. Furthermore, the included study did not assess all of the outcomes prespecified in the review (diabetes-related morbidity, incidence of type 2 diabetes, health-related quality of life, adverse events, socioeconomic effects).

Read the full abstract...
Background: 

Diabetes mellitus, a metabolic disorder characterised by hyperglycaemia and associated with a heavy burden of microvascular and macrovascular complications, frequently remains undiagnosed. Screening of apparently healthy individuals may lead to early detection and treatment of type 2 diabetes mellitus and may prevent or delay the development of related complications.

Objectives: 

To assess the effects of screening for type 2 diabetes mellitus.

Search strategy: 

We searched CENTRAL, MEDLINE, LILACS, the WHO ICTRP, and ClinicalTrials.gov from inception. The date of the last search was May 2019 for all databases. We applied no language restrictions.

Selection criteria: 

We included randomised controlled trials involving adults and children without known diabetes mellitus, conducted over at least three months, that assessed the effect of diabetes screening (mass, targeted, or opportunistic) compared to no diabetes screening.

Data collection and analysis: 

Two review authors independently screened titles and abstracts for potential relevance and reviewed the full-texts of potentially relevant studies, extracted data, and carried out 'Risk of bias' assessment using the Cochrane 'Risk of bias' tool. We assessed the overall certainty of the evidence using the GRADE approach.

Main results: 

We screened 4651 titles and abstracts identified by the search and assessed 92 full-texts/records for inclusion. We included one cluster-randomised trial, the ADDITION-Cambridge study, which involved 20,184 participants from 33 general practices in Eastern England and assessed the effects of inviting versus not inviting high-risk individuals to screening for diabetes. The diabetes risk score was used to identify high-risk individuals; it comprised variables relating to age, sex, body mass index, and the use of prescribed steroid and anti-hypertensive medication. Twenty-seven practices were randomised to the screening group (11,737 participants actually attending screening) and 5 practices to the no-screening group (4137 participants). In both groups, 36% of participants were women; the average age of participants was 58.2 years in the screening group and 57.9 years in the no-screening group. Almost half of participants in both groups were on antihypertensive medication. The findings from the first phase of this study indicate that screening compared to no screening for type 2 diabetes did not show a clear difference in all-cause mortality (hazard ratio (HR) 1.06, 95% confidence interval (CI) 0.90 to 1.25, low-certainty evidence). Screening compared to no screening for type 2 diabetes mellitus showed an HR of 1.26, 95% CI 0.75 to 2.12 (low-certainty evidence) for diabetes-related mortality (based on whether diabetes was reported as a cause of death on the death certificate). Diabetes-related morbidity and health-related quality of life were only reported in a subsample and did not show a substantial difference between the screening intervention and control. The included study did not report on adverse events, incidence of type 2 diabetes, glycosylated haemoglobin A1c (HbA1c), and socioeconomic effects.

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