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Module 4: Screening

Module 4: Screening. Developed through the APTR Initiative to Enhance Prevention and Population Health Education in collaboration with the Brody School of Medicine at East Carolina University with funding from the Centers for Disease Control and Prevention. Acknowledgments.

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Module 4: Screening

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  1. Module 4: Screening Developed through the APTR Initiative to Enhance Prevention and Population Health Education in collaboration with the Brody School of Medicine at East Carolina University with funding from the Centers for Disease Control and Prevention

  2. Acknowledgments This education module is made possible through the Centers for Disease Control and Prevention (CDC) and the Association for Prevention Teaching and Research (APTR) Cooperative Agreement, No. 5U50CD300860. The module represents the opinions of the author(s) and does not necessarily represent the views of the Centers for Disease Control and Prevention or the Association for Prevention Teaching and Research. APTR wishes to acknowledge the following individuals that developed this module: Anna Zendell, PhD, MSW Center for Public Health Continuing Education University at Albany School of Public Health Joseph Nicholas, MD, MPH University of Rochester School of Medicine Mary Applegate, MD, MPH University at Albany School of Public Health Cheryl Reeves, MS, MLS Center for Public Health Continuing Education University at Albany School of Public Health

  3. Presentation Objectives • Define screening and identify appropriate conditions for screening • Evaluate screening tests in terms of their validity, results and generalizability • Evaluate the effectiveness of a screening program and discuss the common biases • Discuss ethical considerations in screening

  4. Introduction to Screening

  5. Oprah’s Full Body Scan http://www.youtube.com/watch?v=6hlMlbmcSHg As you watch this clip and complete the module, think about the implications for patient screening based on this technology Medical concerns? Ethical considerations? Access issues? Informed decision-making after screening?

  6. Preventive Medicine & Public Health • Share common goals • Enhance quality of life of patients • Health promotion • Disease and injury prevention • Preventive medicine promotes these goals at the individual and population levels, while public health focuses on populations.

  7. Prevention – Brief Overview McKenzie et al.: 2008

  8. Screening Defined Presumptive identification of an unrecognized disease through tests, examinations, or other procedures which can be applied rapidly Screening tests sort out apparently well persons who probably have a disease from those who probably do not.

  9. Importance of Screening Jekel et al:, 1996; McKenzie et al:, 2008; Londrigan& Lewenson: 2011 • Early detection • Leads to early treatment • Can lead to a decrease in morbidity and mortality • Can break the chain of transmission and development of new cases • Is often cost-effective • The human body is continually changing

  10. Screening-Diagnosis Connection • Screening starts before diagnosis • History questions • Physical exam findings • Lab tests • Pre-test probability • Results of screening trigger diagnostic work-up and preventive interventions Jekel et al:, 1996; McKenzie et al:, 2008

  11. Screening versus Diagnostic Tests ≠ ScreeningTest Diagnostic Test

  12. Screening versus Diagnostic Tests ≠ ScreeningTest Diagnostic Test Identifies asymptomatic people who may have a disease

  13. Screening versus Diagnostic Tests ≠ ScreeningTest Diagnostic Test Identifies asymptomatic people who may have a disease Determines presence or absence of disease when patient shows signs or symptoms

  14. Characteristics of a Good Screening Test Simple Rapid Inexpensive Safe Available Acceptable

  15. Common Screening Tests

  16. Common Disease Screenings • Pap smear screens for ___________________________ • Fasting blood sugar screens for _________________ • Fecal occult blood test screens for ______________ • Blood pressure screens for ______________________ • Bone densitometry screens for _________________ • PSA test screens for _____________________________ • PPD test screens for _____________________________ • Mammography screens for ______________________ USPSTF: 2009

  17. Common Disease Screenings • Pap smear screens for cervical cancer • Fasting blood sugar screens for diabetes • Fecal occult blood test screens for colorectal cancer • Blood pressure screens for hypertension • Bone densitometry screens for osteoporosis & osteopenia • PSA test screens for prostate cancer • PPD test screens for tuberculosis • Mammography screens for breast cancer. USPSTF: 2009

  18. Weight, Body Mass Index Oral examination Urine test, NMASSIST, or Flagerstrom Tolerance Test for Nicotine Dependency Common Wellness Screenings • Obesity • Dental caries, oral cancer • Drugs, Alcohol, and Tobacco http://www.drugabuse.gov/NIDAMED/screening/

  19. Breast Cancer Screening • Standard practice • Annual mammograms for women age 40+ years • Start earlier if family history of breast cancer • 2009 US Preventive Services Task Force (USPSTF) recommendations • Mammograms not universal for women age 40-50 years • Bi-annual mammograms for women 50+ years • Cost-benefit analysis • False positives • Unnecessary invasive procedures

  20. Colon Cancer Screening • Multiple screening options • Colonoscopy – gold standard • Sigmoidoscopy • Virtual colonoscopy – CT colonoscopy • Barium enema • Fecal testing – occult blood, DNA test • Recommended age, frequency vary by test and family history

  21. Case Study Colorectal Cancer Screening • Practice evaluation of diagnostic test characteristics and screening programs • Discuss prevention concepts • Apply this at patient and population level

  22. Newborn Screening Mandatory universal screen for disorders, including metabolic, hormonal, hematologic, and infectious conditions States vary in what diseases they test for Heel prick blood test 24-48 hours post birth - if done too early, metabolic disease may not show up in blood Family history may indicate need for additional screens

  23. Evaluation of Screening Tests

  24. Evaluating Tests • Reliability and validity are central concepts in evaluating tests • Distinction between reliability and validity • Reliability: consistency of test at different times or under differing conditions • Validity: how well test distinguishes between who has disease and who does not Fortune & Reid: 1998; Jekel et al:, 1996

  25. Characteristics of a Screening Test VALIDITY and RELIABILITY Fortune & Reid: 1998

  26. Reliability Also known as consistency Ability to yield the same results with repeated measurements of same construct Degree to which results are free from random error Jekel: 1996; Al-Eisa: 2009

  27. Common Types of Reliability Intra-subject Jekel: 1996; Al-Eisa: 2009

  28. Common Types of Reliability Intra-rater Intra-subject Jekel: 1996; Al-Eisa: 2009

  29. Common Types of Reliability Intra-rater Intra-subject Inter-rater Jekel: 1996; Al-Eisa: 2009

  30. Common Types of Reliability Intra-rater Intra-subject Inter-rater Instrument Jekel: 1996; Al-Eisa: 2009

  31. Sensitivity • Measures validity of screening tests • Ability to identify those with disease correctly • Minimizes false negatives – if test highly sensitive • SNOUT – Sensitive test with Negative result rules OUT disease

  32. Specificity • Ability to identify those without disease correctly • Minimizes false positives – if test highly specific • SPIN – Specific test with Positive result rules IN disease

  33. Relationship Between Sensitivity and Specificity Morgan TO et al; NEJM, 1996

  34. The 2x2 Table Disease Present Disease Absent True Positive False Positive Test + False Negative True Negative Test -

  35. Sensitivity DISEASE Present Absent Test + Test - Sensitivity= True positives True positives + false negatives

  36. Specificity DISEASE Present Absent Test+ Test- = Specificity True negatives True negatives + false positives

  37. Predictive Values Positive predictive value Negative predictive value

  38. Positive Predictive Value (PPV) • NOT inherent characteristic of a screening test • Percent of positive tests that are truly positive • If test result is positive, what is probability that the patient has the disease? • Is affected by several factors • Specificity & specificity of the screening test • Prevalence of disease

  39. Negative Predictive Value (NPV) • NOT inherent characteristic of a screening test • Percent of negative tests that are truly negative • If test result is negative, what is the probability that patient does not have the disease?

  40. Test Characteristics and Population Tested • Sensitivity and specificity are constant for a particular test • PPV and NPV vary dramatically, depending on prevalence of target condition in population tested • Low prevalence  low PPV, high NPV • High prevalence  high PPV, low NPV

  41. Predictive Value and Prevalence(in test with 98% sensitivity, 92% specificity) Predictive Value Prevalence

  42. Predictive ValuesSample Calculations

  43. Positive Predictive ValueLow Prevalence

  44. Positive Predictive ValueHigh Prevalence

  45. Positive Predictive ValueVery High Prevalence

  46. Multiple Screening TestsSimultaneous • Use of different tests concurrently to screen for same condition • Example: Prenatal multiple marker screening for Down Syndrome • Measures levels of 3 biomarkers in mother’s blood: • AFP: alpha-fetoprotein, protein produced by fetus • hCG: human chorionic gonadotropin, hormone produced by placenta • Estriol: a hormone produced by both fetus and placenta • Results of ALL 3 tests increases sensitivity and specificity

  47. Multiple Screening TestsSequential • Use of two-stage screening to target testing efforts • Example: Early pregnancy gestational diabetes screening • First trimester risk assessment—identifies women at higher risk of gestational diabetes • Oral Glucose Tolerance Test (OGTT) right away for those whose first screen indicates high risk

  48. Multiple Screening TestsSequential • Two-stage screening to maximize predictive value • Example: HIV screening in suburban primary care office • Risk assessment questionnaire about sexual and drug use history • HIV blood test for all patients whose questionnaire indicates risk factors for HIV infection

  49. Effectiveness of Screening Programs

  50. Screening Effectiveness Evaluation • Test characteristics (sensitivity & specificity) alone are never sufficient for a sound decision about whether to use a screening test • Other screening considerations • Benefits vs. risks • Prevalence of target condition • Inconvenience • Costs/resource expenditures • Patient values and cultural norms Guyatt: 2009

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