EAL

DM: Prevention and Treatment of CVD (2007)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To conduct a meta-analysis of observational studies of the association between glycosylated hemoglobin and cardiovascular disease in diabetic persons.

Inclusion Criteria:

prospective cohort studies that examined the cardiovascular outcomes of interest
studies that reported a measure of HbA1c and that were conducted in samples that included persons with type 1 or type 2 diabetes

Exclusion Criteria:

study had no original data
study did not address persons with diabetes
involved non-prospective studies, such as cross-sectional and retrospective case-control studies
had less than 1 year of follow up
assessed the effect of glycemic control on cardiovascular outcomes after admission to a hospital or after surgery
involved only patients receiving dialysis or transplants

Description of Study Protocol:

Recruitment (article search)

Medline database
articles in English published between 1996 to July 2003
search terms: coronary heart disease, peripheral artery disease, cerebrovascular disease, diabetes mellitus, glycemic control, and glycosylated hemoglobin
when more than one article reported data from the same study, such as the United Kingdom Prospective Diabetes Study, then the most recent was used

Design :

two investigators independently reviewed each article for inclusion
for studies included, investigators abstracted odds ratios, relative risks, or relative hazards for the association between cardiovascular risk and baseline or updated mean HbA1c values

Blinding used (if applicable): not applicable

Intervention (if applicable): not applicable

Statistical Analysis

separate meta-analyses for study samples for persons with type 1 and type 2 DM for the the different cardiovascular outcomes
meta-analytic comparison based on the adjusted summary relative risk estimate from each cohort study, using the most fully adjusted multivariable model.
the relative risk estimate from each cohort study was converted to reflect a 1-unit increase in percentage HbA1c.
a random effects model was used to pool the effect estimates
pooled estimates of risk were combined with separate estimates of inverse variance-weighted log risk ratio estimates from each study using a random-effects model
publication bias assessed using the Begg and Egger test and funnel plots
sensitivity analyses assessed the relative influence of each study in each subgroup analysis by omitting 1 study at a time to assess the influence of any single study on the pooled estimate.

Data Collection Summary:

Timing of Measurements: not applicable

Dependent Variables

fatal and non-fatal myocardial infarction, angina, or ischemic heart disease
fatal and nonfatal stroke
peripheral artery disease

Independent Variables

type of diabetes

Control Variables

Description of Actual Data Sample:

Initial N:Search yielded 694 articles, 69 were reviewed and 17 studies included: mean sample sizes ranging from 94-5102

Attrition (final N): as above

Age: mean age of subjects in the 17 studies ranged from 27 to 69

Ethnicity: not specified

Other relevant demographics: percentage of males ranged from 32% to 100%

Anthropometrics not specified

Location: studies were from the US, Finland, Sweden, New Zealand, Denmark, United Kingdom, Italy, and Germany.

Summary of Results:

Type 1 diabetes

The pooled relative risk for the 3 prospective stuides of HbA1c and CHD in persons with type 1 diabetes was 1.15 (95% CI, 0.92 to 1.43) for each 1-percentage point increase in HbA1c.
For the two studies of HbA1c and peripheral artery disease the pooled relative risk was 1.32 (CI, 1.19 to 1.45)

Type 2 diabetes

total CVD: the pooled relative risk (studies) was 1.18 (CI, 1.10 to 1.26) for each 1-percentage point increase in HbA1c.
risk of CAD the pooled risk (5 studies) was 1.13 (CI, 1.06 to 1.20) for each 1-percentage increase in HbA1c
fatal CHD: the relative risk (5 studies) was 1.16 (CI, 1.07 to 1.26) for each 1-percentage increase in HbA1c
stroke (3 studies: pooled relative risk of 1.17 (CI, 1.09 to 1.25)
peripheral artery disease: pooled relative risk (3 studies) was 1.28 (CI, 1.18-1.39)

Other Findings

sensitivity analyses indicated that all of the studies included seemed to contribute relatively equally to the estimate.
evidence of publication bias: the larger, more precise studies tended to show smaller relative risk estimates.

Author Conclusion:

Improvements in glycemic control may lower the risk for CVD in persons with diabetes.

Funding Source:

Reviewer Comments:

Quality Criteria Checklist: Review Articles
Relevance Questions
	1.	Will the answer if true, have a direct bearing on the health of patients?	Yes
	2.	Is the outcome or topic something that patients/clients/population groups would care about?	Yes
	3.	Is the problem addressed in the review one that is relevant to dietetics practice?	Yes
	4.	Will the information, if true, require a change in practice?	Yes

Validity Questions
	1.	Was the question for the review clearly focused and appropriate?	Yes
	2.	Was the search strategy used to locate relevant studies comprehensive? Were the databases searched and the search termsused described?	Yes
	3.	Were explicit methods used to select studies to include in the review? Were inclusion/exclusion criteria specified andappropriate? Wereselectionmethods unbiased?	Yes
	4.	Was there an appraisal of the quality and validity of studies included in the review? Were appraisal methodsspecified,appropriate, andreproducible?	Yes
	5.	Were specific treatments/interventions/exposures described? Were treatments similar enough to be combined?	Yes
	6.	Was the outcome of interest clearly indicated? Were other potential harms and benefits considered?	Yes
	7.	Were processes for data abstraction, synthesis, and analysis described? Were they applied consistently acrossstudies and groups? Was thereappropriate use of qualitative and/or quantitative synthesis? Was variation in findings among studies analyzed? Were heterogeneity issued considered? If data from studies were aggregated for meta-analysis, was the procedure described?	Yes
	8.	Are the results clearly presented in narrative and/or quantitative terms? If summary statistics are used, are levels ofsignificance and/or confidence intervals included?	Yes
	9.	Are conclusions supported by results with biases and limitations taken into consideration? Are limitations ofthe review identified anddiscussed?	Yes
	10.	Was bias due to the review's funding or sponsorship unlikely?	Yes