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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
