Screening Tests

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Screening Tests

• Thomas B. Newman, MD, MPH
• Andi Marmor, MD, MSEd
• October 22, 2009

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Administrative stuff

• Winners and Losers on website this week and for
  Chapter 12
• NYT article on website

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Overview

• Introduction
• Context
• Defintions
• Problems with observational studies
• Problems with randomized trials
• Conclusion ecologic view

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International Comparison of Spending on Health,
19802006
Average spending on healthper capita (US PPP)
Total expenditures on healthas percent of GDP
Data OECD Health Data 2008 (June 2008). From
Commonwealth fund
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Preventable deaths
Davis K. NEJM 3591751, 10/23/08
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Screening tests TN Biases

• When your only tool is a hammer, you tend to see
  every problem as a nail.
• Biggest gains in longevity have been PUBLIC
  HEALTH interventions, not interventions aimed at
  individuals
• Biggest threats are still public health threats
• Interventions aimed at individuals are
  overemphasized because they are more profitable

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Cultural characteristics
"We live in a wasteful, technology driven,
individualistic and death-denying culture."
--George Annas, New Engl J Med, 1995
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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.
• Disease vs. condition
• Asymptomatic vs. no known signs or symptoms

Common screening tests. David M. Eddy, editor.
Philadelphia, PA American College of Physicians,
1991
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Screening tests may be history questions
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Screening Spectrum
Recognized symptomatic disease
Presymp-tomatic disease
Risk factor
Unrecognized symptomatic disease
Decreasing numbers labeled and treated
Decreasing difficulty demonstrating benefit
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Examples and overlap

• Unrecognized symptomatic disease vision and
  hearing problems in young children iron
  deficiency anemia, depression
• Presymptomatic disease neonatal hypothyroidism,
  syphilis, HIV
• Risk factor hypercholesterolemia, hypertension
• Somewhere between prostate cancer, ductal
  carcinoma in situ of the breast, more severe
  hypertension

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Its just a simple blood test.
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Possible harms from screening

• To all tested
• To those with negative results
• To those with positive results
• To those not tested
• See Chapter 6

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Source Funny Times. (1-888-Funnytimes x 476)
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Forces behind excessive screening -1

• Companies selling machines to do the test
• Companies selling the test itself
• Companies selling products to treat the condition
• Clinicians who treat the condition
• Politicians who are (or want to appear)
  sympathetic

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Forces behind excessive screening -2

• Disease research and advocacy groups
• Academics who study the condition
• Clinicians doing or interpreting the test
• Managed care organizations
• The public

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