Thomas B. Newman, MD, MPH Andi Marmor, MD, MSEd October 23, 2008

Outline  Overview and definitions  Can screening be bad?  Evaluating studies of screening tests Observational studies of screening Randomized trials of screening  Conclusion

Outline  Overview and definitions  Can screening be bad?  Evaluating studies of screening tests Observational studies of screening Randomized trials of screening  Conclusion

What is screening?  Common definition: “Testing to detect asymptomatic disease”  Better definition*: “Application of a test to detect a potential disease or condition in people with no known signs or symptoms of that disease or condition” *Common screening tests. David M. Eddy, editor. Philadelphia, PA: American College of Physicians, 1991

What is screening?  Common definition: “Testing to detect asymptomatic disease”  Better definition*: “Application of a test to detect a potential disease or condition in people with no known signs or symptoms of that disease or condition” *Common screening tests. David M. Eddy, editor. Philadelphia, PA: American College of Physicians, 1991

What is screening?  Common definition: “Testing to detect asymptomatic disease”  Better definition*: “Application of a test to detect a potential disease or condition in people with no known signs or symptoms of that disease or condition”  “ Condition” includes a risk factor for a disease… *Common screening tests. David M. Eddy, editor. Philadelphia, PA: American College of Physicians, 1991

Screening Spectrum Risk factor Recognized symptomatic disease Presymptomatic disease Unrecognized symptomatic disease è Fewer people è Easier to demonstrate benefit è Less potential for harm

Screening Spectrum Risk factor Recognized symptomatic disease Presymptomatic disease Unrecognized symptomatic disease è Fewer people è Easier to demonstrate benefit è Less potential for harm

Issues in Screening for Risk Factors  Risk factor treatment disease Does risk factor predict disease? Does treatment of risk factor reduce disease? ○ Does treatment reduce risk factor?  Test “accuracy” must measure incidence of disease over time Most measures of test accuracy apply to disease that is prevalent at the time the test is done  Potential for harm greatest when screening for risk factors!

Screening Spectrum Risk factor Recognized symptomatic disease Presymptomatic disease Unrecognized symptomatic disease è Fewer people recognized and treated è Easier to demonstrate benefit è Less potential for harm

Goals of Screening for Presymptomatic Disease  Detect disease in earlier stage than would be detected by symptoms Only possible if an early detectable phase is present (latent phase) Only beneficial if earlier treatment is more effective than later treatment  Do this without incurring harm to the patient Net benefit must exceed net harm Long follow up and RCT may be needed to prove

Special Case: Screening for Cancer  Natural history heterogeneous Screening test may pick up slower growing or less aggressive cancers Not all patients diagnosed with cancer will become symptomatic  Diagnosis is subjective There is no gold standard

Outline  Overview and definitions  Can screening be bad?  Evaluating studies of screening tests Observational studies of screening Randomized trials of screening  Conclusion

Possible harms from screening  To all  To those with negative results  To those with positive results

Possible harms from screening  To all  To those with negative results  To those with positive results

Possible harms from screening  To all  To those with negative results  To those with positive results

Source: Funny Times. (1-888-Funnytimes x 476)

Possible harms from screening  To all tested  To those with negative results  To those with positive results

Forces Behind Excessive Screening  Economic  Political  Health care providers  Public/cultural

Forces Behind Excessive Screening  Economic  Political  Health care providers  Public/cultural

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