|The efficacy and cost of alternative strategies for systematic screening for Type 2 diabetes in the U.S. population 45 - 74 years of age
|Johnson S L, Tabaei B P, Herman W H
This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn.
Several screening strategies for Type 2 diabetes were examined:
screening with a random plasma glucose (RPG) cut point of 100 mg/dL, a highly sensitive test;
screening with an RPG cut point of 160 mg/dL, a highly specific test;
screening with an RPG cut point of 130 mg/dL, a test with intermediate sensitivity and specificity; and
screening with a multivariate logistic equation that incorporated RPG, postprandial time (self-reported number of hours since last food or drink other than water), age, gender and body mass index.
Three screening intervals over a 15-year period were considered. These were baseline and every 5 years, baseline and every 3 years, and baseline and every year. Thus, 12 strategies were evaluated.
Regardless of the screening strategy, individuals with positive screening tests but an RPG <200 mg/dL underwent an oral glucose tolerance test (OGTT) for definitive diagnosis, while those with positive screening tests and an RPG >/= 200 mg/dL had a fasting plasma glucose (FPG) test for definitive diagnosis.
Economic study type
The study population comprised a hypothetical cohort of non-diabetic individuals aged 45 to 74 years, who were representative of the US population.
The setting was primary care. The economic study was carried out in the USA.
Dates to which data relate
The effectiveness data were derived from studies published between 1997 and 2003. No dates for the resource use data were explicitly reported. The price year was not reported.
Source of effectiveness data
The effectiveness evidence was derived from a synthesis of completed studies.
Outcomes assessed in the review
The outcomes assessed from the literature were:
the size of the eligible US population that could undergo screening;
the sensitivity and specificity of the screening strategies; and
the prevalence and progression of Type 2 diabetes.
Study designs and other criteria for inclusion in the review
The primary studies appear to have been identified selectively and a systematic review of the literature was not carried out. Some data came from US statistics.
Sources searched to identify primary studies
Criteria used to ensure the validity of primary studies
Methods used to judge relevance and validity, and for extracting data
Number of primary studies included
Four primary studies provided clinical data.
Methods of combining primary studies
A narrative approach was used to combine the primary estimates.
Investigation of differences between primary studies
Results of the review
The analysis of US statistics showed that 80.3 million people were aged 45 to 74 years, of which 7.7 million had been diagnosed with diabetes. Therefore, 72.6 million individuals were eligible for screening.
For RPG >/= 100 mg/dL, the sensitivity was 91% and the specificity 49%;
for RPG >/= 130 mg/dL, the sensitivity was 63% and the specificity 87%; and
for RPG >/= 160 mg/dL, the sensitivity was 44% and the specificity 96%.
The equation was 63% sensitive and 96% specific.
The prevalence of undiagnosed diabetes was 10% at baseline and the prevalence of impaired glucose tolerance (IGT) and/or impaired fasting glucose (IFG) was 22%.
The rate of progression from IGT or IFG to diabetes was 5.7% per year.
Measure of benefits used in the economic analysis
The summary benefit measure was the number of true-positive cases associated with each screening strategy. The number of false-positive cases was also reported.
Discounting was not relevant since the costs were incurred during a short timeframe. The unit costs were presented, but there was limited information on resource use. The health services included in the analysis were physician time, RPG tests, diagnostic FPGs and OGTTs. For individuals who sought care, it was assumed that screening was opportunistic and that the only direct medical cost was that of the screening test and, when required, the cost of a diagnostic FPG or OGTT. For those who had not sought medical care, the direct medical cost of screening included the cost of an outpatient visit, the screening test, and, when required, the diagnostic FPG or OGTT. The cost/resource boundary of the health care system appears to have been adopted in the analysis of the direct costs. The source of the cost data was not explicitly stated. Resource use was presumably based on authors' assumptions. The price year was not reported.
Statistical analysis of costs
The costs were treated deterministically.
The indirect costs (i.e. patient time and travel) were included in the economic evaluation. The unit costs were reported. The source of the data was not stated, although it could have been a study published in 2003. The resource use data were not given. The price year was not reported. Discounting was not applied.
Sensitivity analyses were not performed.
Estimated benefits used in the economic analysis
The number (in millions) of true-positive cases (true-negative cases) with RPG >/= 100 mg/dL was 18.5 (485.9) every year, 18.3 (182.3) every 3 years, and 18.2 (121.6) every 5 years.
The number (in millions) of true-positive cases (true-negative cases) with RPG >/= 130 mg/dL was 18.1 (124.2) every year, 17.3 (46.5) every 3 years, and 16.4 (31.3) every 5 years.
The number (in millions) of true-positive cases (true-negative cases) with RPG >/= 160 mg/dL was 17.6 (38.1) every year, 15.7 (14.3) every 3 years, and 14.0 (9.5) every 5 years.
The number (in millions) of true-positive cases (true-negative cases) with the equation was 18.1 (38.1) every year, 17.3 (14.3) every 3 years, and 16.4 (9.5) every 5 years.
The total cost (in billions) with RPG >/= 100 mg/dL was $42.7 every year, $16.8 every 3 years, and $11.6 every 5 years.
The total cost (in billions) with RPG >/= 130 mg/dL was $27.4 every year, $11.1 every 3 years, and $7.8 every 5 years.
The total cost (in billions) with RPG >/= 160 mg/dL was $24 every year, $9.8 every 3 years, and $6.9 every 5 years.
The total cost (in billions) with the equation was $24.4 every year, $9.7 every 3 years, and $6.9 every 5 years.
Synthesis of costs and benefits
Average cost-effectiveness ratios were calculated to combine the costs and benefits of the screening strategies.
The average cost per true-positive case with RPG >/= 100 mg/dL was $2,312 every year, $916 every 3 years, and $637 every 5 years.
The average cost per true-positive case with RPG >/= 130 mg/dL was $1,513 every year, $642 every 3 years, and $475 every 5 years.
The average cost per true-positive case with RPG >/= 160 mg/dL was $1,359 every year, $626 every 3 years, and $492 every 5 years.
The average cost per true-positive case with the equation was $1,348 every year, $563 every 3 years, and $419 every 5 years.
The costs were lower for opportunistic screening than for population screening. For example, considering a strategy using a cut point of 130 mg/dL every 3 years, the cost per true positive for opportunistic screening was $275, while for population screening the cost per true positive was $1,745.
An approach that balanced sensitivity and specificity, such as a random plasma glucose (RPG) with a cut point of 130 mg/dL or a multivariate equation applied every 3 years, was optimal for the screening of Type 2 diabetes in the general population.
CRD COMMENTARY - Selection of comparators
A rationale for the selection of the comparators was provided. The choice of RPG was made on the basis of American Diabetes Association recommendations. The equation was also appropriately considered among the potential comparators. Different cut point and frequency levels were investigated. However, the authors stated that the analysis did not cover all possible screening strategies. Further, FPG is not commonly performed in routine clinical practice. You should decide whether they are valid comparators in your own setting.
Validity of estimate of measure of effectiveness
The clinical data came from published studies. It would appear that a review of the literature was not undertaken to identify primary studies. Most of the data were extracted from US statistics. Since there was no information on the other sources of evidence, it was not possible to assess the validity of the primary studies. Further, uncertainty in the clinical data was not investigated in a sensitivity analysis.
Validity of estimate of measure of benefit
The benefit measure was specific to the disease considered in the study and is not comparable with the benefits of other health care interventions. However, it might be a relevant measure for strategies of screening for diabetes in the general population.
Validity of estimate of costs
The chosen perspective was appropriate because costs relevant to both the health care system and the patients were included in the analysis. The unit costs were reported, while information on resource use appears to have been based on authors' opinions. It was unclear whether this reflected typical treatment patterns. The source of the data was unclear and the price year was not reported.
The authors did not make extensive comparisons of their findings with those from other studies. They also did not address the issue of the generalisability of the study results to other settings. Sensitivity analyses were not carried out, which limits the external validity of the study. The use of an incremental analysis would have been helpful in identifying the most cost-effective option. The authors noted that it was not possible to determine whether the costs of screening were balanced by clinical benefits of earlier diagnosis and treatment.
Implications of the study
The study results suggested that screening strategies that balance sensitivity and specificity, such as RPG with a cut point of 130 mg/dL or a multivariate equation, provide good yield and minimise false-positive tests and costs.
Johnson S L, Tabaei B P, Herman W H. The efficacy and cost of alternative strategies for systematic screening for Type 2 diabetes in the U.S. population 45 - 74 years of age. Diabetes Care 2005; 28(2): 307-311
Other publications of related interest
Stratton IM, Adler AI, Neil HA, et al. Association of glycaemia with macrovascular and microvascular complications of type 2 diabetes (UKPDS 35): prospective observational study. BMJ 2000;321:405-12.
Subject indexing assigned by NLM
Aged; Blood Glucose; Cost-Benefit Analysis; Diabetes Mellitus, Type 2 /diagnosis /economics /epidemiology; False Negative Reactions; False Positive Reactions; Glucose Tolerance Test; Health Expenditures; Humans; Incidence; Mass Screening /economics /methods /standards; Middle Aged; Multivariate Analysis; Prevalence; United States /epidemiology
Date bibliographic record published
Date abstract record published