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 screeningRandomized trials of screening

Conclusion

Outline

Overview and definitions Can screening be bad? Evaluating studies of screening tests

Observational studies of screeningRandomized 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

Fewer people Easier to demonstrate benefit Less potential for harm

Screening Spectrum

Risk factor

Recognized symptomatic disease

Presymptomatic disease

Unrecognized symptomatic disease

Fewer people Easier to demonstrate benefit 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 timeMost 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

Fewer people recognized and treated Easier to demonstrate benefit Less potential for harm

Goals of Screening for Presymptomatic Disease Detect disease in earlier stage than would

be detected by symptomsOnly 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

patientNet benefit must exceed net harmLong 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 subjectiveThere is no gold standard

Outline

Overview and definitions Can screening be bad? Evaluating studies of screening tests

Observational studies of screeningRandomized 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

Ad sponsored by Schering: company that

makes interferon.

Continue to Part 2