Cost-effectiveness of Screening Tests Mark Hlatky, MD Stanford University

Screening Principles  Goal is to find disease “early” when it is simpler to treat  Best examples are in cancer  Value of screening program depends on  Disease characteristics  Test performance, cost  Treatments available for identified disease

Screening Principles: Disease  Disease to be screened should be  Serious - irreversible effects  Prevalence is high in target population  Natural history allows early detection t 0 t 1 t 2 t 0 t 1 t 2 1 st Develops 1 st Detectable 1 st Symptoms 1 st Develops 1 st Detectable 1 st Symptoms t 2 – t 1 should be long for effective screening

Screening Principles: Test  Good screening test is  Sensitive AND specific to detect disease OR  Separates high and low risk to develop disease  Acceptable to patients  Safe  Cheap

Screening Principles: Therapy  Effective therapy available  For affected patient  To avoid spread of disease  Therapy should be either better or cheaper when given early

CEA of Screening Tests  Cost-effectiveness has examined therapies  Bypass surgery for angina  Statins for high cholesterol  Therapies have direct effect on outcome  CE weighs improvement in outcome against increase in cost  Screening tests provide information  Indirect effects on outcome  CE of tests is more difficult to judge, since it depends on how test results are used to change therapy

Screening Tests: Cost  Total costs include the cost of  Test itself  Follow-up tests  Subsequent treatment  Complications of tests, therapy

Screening Tests: Effectiveness  Direct health benefits minor  Low risk or absence of disease is reassuring, but  “Labelling” can be harmful  Most benefits are due to changing therapy  Adding effective drugs  Potential value of positive test in improving adherence to preventive therapy  But EBCT results didn’t change patient behavior in the PACC randomized trial JAMA 2003; 289:

Screening Tests: Incremental Information  Information from test may be redundant or available more simply, cheaply  Clinical history very useful for CHD risk  Framingham risk score  Alternative tests  Imaging, biomarkers, genetic tests of risk?  Cost-effectiveness always compares 2 or more alternatives

Tests and Treatment Thresholds  Prototype decision is to  Treat without testing  Test, treat if positive  No treatment, no test  Optimal strategy depends on  Pretest probability or risk  Test sensitivity/specificity or relative risk of test results  Effectiveness of treatment

Tests and Treatment Thresholds  Optimal strategy is:  Low probability/risk -- no therapy, no test  Intermediate probability/risk – test, treat if results positive  High probability/risk – treat w/o testing High NeitherTestTreat N Engl J Med. 1980;302: Low

Diagnostic Test Evaluation  Case series usual source of information  Correlation with “gold standard”  Prediction of prognosis  Randomized studies of tests are unusual  Invasive vs conservative evaluation strategies post-MI  BNP testing of pts with acute dypnea  Mammography

CEA of Screening Tests  Cost-effectiveness measures “value for money spent”  Costs include follow-up tests; therapy  Effectiveness measure is outcome  Test gives information  Effect on outcome is indirect  Evaluation must consider value compared with  Clinical history  Other tests