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

APTR wishes to acknowledge the following individuals that developed this module:

Anna Zendell, PhD, MSWCenter for Public Health Continuing EducationUniversity at Albany School of Public Health

Joseph Nicholas, MD, MPHUniversity of Rochester School of Medicine

Mary Applegate, MD, MPHUniversity at Albany School of Public Health

Cheryl Reeves, MS, MLSCenter for Public Health Continuing EducationUniversity at Albany School of Public Health

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.

Presentation Objectives

1. Define screening and identify appropriate conditions for screening

2. Evaluate screening tests in terms of their validity, results and generalizability

3. Evaluate the effectiveness of a screening program and discuss the common biases

4. Discuss ethical considerations in screening

Introduction to Screening

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?

http://www.youtube.com/watch?v=6hlMlbmcSHg

Oprah’s Full Body Scan



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.

Primary Prevention

Secondary Prevention

Tertiary Prevention

Prevention – Brief Overview

McKenzie et al.: 2008

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.

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

Jekel et al:, 1996; McKenzie et al:, 2008; Londrigan & Lewenson: 2011

Importance of Screening

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

Screening versus Diagnostic Tests

Diagnostic Test

Screening Test ≠


Diagnostic Test

Screening Test ≠Identifies asymptomatic people who may have a disease


Screening Test ≠Identifies asymptomatic people who may have a disease

Diagnostic Test

Determines presence or absence of disease when patient shows signs or symptoms

Characteristics of a Good Screening Test

Simple Rapid Inexpensive Safe Available Acceptable

Common Screening Tests

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

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

Obesity Dental caries, oral cancer Drugs, Alcohol, and

Tobacco

Weight, Body Mass Index Oral examination Urine test, NMASSIST, or

Flagerstrom Tolerance Test for Nicotine Dependency

http://www.drugabuse.gov/NIDAMED/screening/

Common Wellness Screenings

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

Breast 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

Colon Cancer Screening

Case Study Colorectal Cancer Screening

Practice evaluation of diagnostic test characteristics and screening programs

Discuss prevention concepts

Apply this at patient and population level

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

Newborn Screening

Evaluation of Screening 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

Evaluating Tests

Characteristics of a Screening Test

VALIDITY and RELIABILITY

Fortune & Reid: 1998

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

Reliability


Intra-subject

Common Types of Reliability

Intra-subject

Intra-rater



Intra-subject

Inter-rater

Intra-rater



Intra-subject

Instrument Inter-rater

Intra-rater



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

Sensitivity

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

disease

Specificity

Relationship Between Sensitivity and Specificity

PSA level Sensitivity Specificity

1.0 100 21

2.0 100 48

3.0 100 60

4.0 99 73

5.0 96 76

6.0 94 79

7.0 90 83

8.0 90 88

9.0 68 90

10.0 54 93

11.0 47 94

12.0 30 95

13.0 23 96

14.0 17 97

15.0 11 97 Morgan TO et al; NEJM, 1996

The 2x2 Table

True Positive

Disease Present Disease Absent

Test +

Test -

False Positive

False Negative

True Negative

Sensitivity=

True positive False positive

False negative True negative

Present AbsentDISEASE

Test +

Test -

True positives

True positives + false negatives

Sensitivity

Specificity

True positive False positive

False negative True negative

Present AbsentDISEASE

Test +

Test -

= SpecificityTrue negatives

True negatives + false positives

Predictive Values

Positive predictive value Negative predictive value

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

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?

Sensitivity and specificity are constant for a particular test

PPV and NPV vary dramatically, depending on prevalence of target condition in population testedLow prevalence low PPV, high NPVHigh prevalence high PPV, low NPV

Test Characteristics and Population Tested

0%

20%

40%

60%

80%

100%

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

PVPPVN

Prevalence

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

Pred

ictiv

e Va

lue

Disease

Diseased Non-Diseased PVs↓

Test Result

Positive True Positive (TP) False Positive (FP) (Type 1 error)

TPTP + FP

Negative False Negative (FN)(Type II error) True Negative (TN) TN

TN +FN

SensitivityTP TP + FN

SpecificityTN

TN + FP

Predictive ValuesSample Calculations

HIV Status

1,000 people at Prenatal Clinic HIV-Positive (15) HIV-Negative (985) 1.5% Prevalence

ELISA Result

Positive True Positive (14) False Positive (99)14

14 + 99= 12.4% PPV

Negative False Negative (1) True Negative (886)886

1 + 886= 99.9% NPV

Sensitivity (95%) Specificity (90%)

Positive Predictive ValueLow Prevalence

HIV Status

1,000 people at STD Clinic HIV-Positive (60) HIV-Negative (940) 6% Prevalence

ELISA Result


57 + 94= 37.75% PPV


3 + 846= 99.6% NPV


Positive Predictive ValueHigh Prevalence

HIV Status

1,000 people at Clinic in Zambia HIV-Positive (240) HIV-Negative (760) 24% Prevalence

ELISA Result


228 + 76= 75% PPV


12 + 684= 98.3% NPV


Positive Predictive ValueVery High Prevalence

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

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

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

Effectiveness of Screening Programs

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

Screening Effectiveness Evaluation

Assessing a screening/diagnostic test Properties & accuracy Comparison of test to “gold standard”

Most definitive diagnostic procedure or best available laboratory test

Not always a gold standard for a procedure

USPSTF recommended

Study DesignTesting a Test

USPSTF Activities

Systematically reviews the evidence of effectiveness and develops recommendations for clinical preventive services

Recommendations include: Screening tests Counseling Preventive medications

Courtesy of Diana Pettiti, USPSTF: 2010

USPSTF Methodology

1. Define analytic framework – outcomes & questions2. Define and retrieve relevant evidence 3. Evaluate QUALITY of studies (good, fair, poor)4. Synthesize and judge STRENGTH of overall

evidence (convincing, adequate, inadequate)5. Determine BALANCE of benefits and harms

Benefits – Harms = Net Benefit6. Link recommendation to judgment about net

benefits: Grades: A, B, C, D, I (inadequate evidence)


Critical Appraisal Questions

Do the studies have the appropriate research design to answer key questions?

Are the existing studies high quality?

Are the results of the studies applicable to the general US primary care population and setting?


Critical Appraisal Questions

How many relevant studies have been done?

How large are the studies?

How consistent are the results of the studies?

Are there other factors that help us assess the certainty of the evidence? (e.g. dose-response effects, biologic plausibility)


Certainty of Net Benefit Magnitude of Net Benefit

Substantial Moderate Small Zero/negative

High A B C D

Moderate B B C D

Low Insufficient (I Statement)


Linking Recommendations to Benefits: USPSTF Recommendations

Grade Grade Definition Suggestion for PracticeA USPSTF recommends the service.

There is high certainty that the net benefit is substantial. Offer or provide this service.

BThe USPSTF recommends the service. There is high certainty that the net benefit is moderate or there is moderate certainty that the net benefit is moderate to substantial.

Offer or provide this service.

CUSPSTF recommends against routinely providing the service. There may be considerations that support providing the service in an individual patient.There is moderate or high certainty that the net benefit is small.

Offer or provide this service only if there are other considerations in support of the offering or providing the service in an individual patient.

DUSPSTF recommends against the service. There is moderate or high certainty that the service has no net benefit or that the harms outweigh the benefits.

Discourage the use of this service.

IUSPSTF concludes that the current evidence is insufficient to assess the balance of benefits and harms of the service. Evidence is lacking, of poor quality, or conflicting, and the balance of benefits and harms cannot be determined.

Read “Clinical Considerations” section of USPSTF Recommendation Statement. If offered the service, patients should understand the uncertainty about the balance of benefits and harms.


Communicating USPSTF Recommendations

Newer tests vs. gold standard Best tests for your population

Validity in your population Accessibility Cost Capacity of local health care system

Need a system in place to be able to screen AND to deal with positive results

Comparison of Screening Tools

Liquid-basedPap smear –the NEW test

Patients withoutevidence of cervical cancer

NOCervical Cancer

NOCervical Cancer

Cervical Cancer

Cervical CancerStandardPap smear –the GOLD STANDARD

Testing a Test

1. Are study methodology and results credible?

2. Have sensitivity, specificity and predictive values been calculated and reported?

3. Is the population tested similar to my patient population?

4. How can I use these results in a screening program or patient care?

5. Does this screening improve the present state of medical screening?

Evaluating Screening Research

Lead time bias: over-estimation of survival rate among screening-detected cases

When survival is calculated from diagnosis point

Length bias: over-estimation of survival rate among screening-detected cases

Due to excess of slowly progressing cases among those identified by screening

Koretz: 2009

Screening Outcome ConsiderationsLong-term Outcomes

To Screen or Not to ScreenEssential Criteria

Disease Test Treatment Cost ProgrammingCondition should be important health problem.

Test must be simple, safe, precise, valid.

Must be evidence of effective treatment and that early treatment will lead to better outcomes.

Evidence on cost- effectiveness of screening for interventions and outcomes.

Evidence from randomized controlled trials that program effective in reducing mortality and morbidity.

Epidemiology of disease must be understood.

Must be acceptable to population and health providers giving test.

Benefits outweigh physical and psychological harms if any.

Criteria/protocol on next steps for positive tests.

Protocols for implementation and evaluation of screening program.

Pseudodisease

Definition: Identifying a disease that is unlikely to impact patient over lifetime Prostate or breast cancer may be present in body May never become clinically apparent

Identifying pseudodisease is nearly impossible until person dies from unrelated causes

Gold standard tests cannot predict future trajectory of a condition

Durgin: 2005

Screening and Ethics

Mandated screening Genetic testing Disparities Creation of screening program

Ethical Considerations

Newborn screening Syphilis testing for marriage licenses TB screening for health care workers Drug testing for airline pilots

Mandatory Screening

Need to assess costs vs. benefits at all levels Individual Societal Healthcare system

Mandatory Screening

Pros Identify serious problems that could harm others OR where

immediate treatment is imperative Cons

Potential harm to patient autonomy Confidentiality concerns Testing low risk population reduces PPV Consequences of false positive tests

Mandatory Screening

Learn if individual carries a gene for a disease and might pass it on to children

Screen unborn fetus for disease Test for genetic diseases in children or adults before

symptoms emerge

Genetics TestingBenefits

Results difficult to interpret; not always clear cut Employment issues Health/life insurance consequences Added stress Costs Confidentiality Ownership of DNA

Genetic TestingConcerns

Kalb, 2006

DisparitiesAccess to Screening

Geographic region Rural Inner city

Uninsured and underinsured Screening and follow-up testing/treatment Cost-prohibitive without health insurance

Minority and immigrant populations Lack of culturally competent healthcare providers Low health literacy

Cross-cultural differences in health literacy and attitudes

Culturally relevant screening Screening practices may need to be adapted

DisparitiesCultural

How ethical is it to: Use a test that may tell people they have condition

when they do not? Use a test that may tell people they do not have

condition when they actually do? Use a test if there is no system in place to treat those

who test positive?

Developing a Screening ProgramEthical Considerations

Truglio et al: 2011

Strategic targeting for screening Groups with higher prevalence – increase PPV Provider vs. patient – who is more likely to request?

Growing body of evidence-based medicine allows us to: Identify more precise screening protocols Weigh benefits/drawbacks of screening test

Strategic screening can be cost-effective

Implications for Practice

Summary

Screening is bedrock of secondary prevention Screening and diagnosis are not the same Sensitivity and specificity are characteristics of a

screening test that determine a test’s validity Predictive values are affected by sensitivity &

specificity of test and by prevalence of the disease Screening of high-risk populations increases positive

predictive value Screening decisions must weigh acceptability and

applicability to practitioner, population, and individual

Collaborating Institutions

Department of Public HealthBrody School of Medicine at East Carolina University

Department of Community & Family MedicineDuke University School of Medicine

Advisory Committee

Mike Barry, CAELorrie Basnight, MDNancy Bennett, MD, MSRuth Gaare Bernheim, JD, MPHAmber Berrian, MPHJames Cawley, MPH, PA-CJack Dillenberg, DDS, MPHKristine Gebbie, RN, DrPHAsim Jani, MD, MPH, FACP

Denise Koo, MD, MPHSuzanne Lazorick, MD, MPHRika Maeshiro, MD, MPHDan Mareck, MDSteve McCurdy, MD, MPHSusan M. Meyer, PhDSallie Rixey, MD, MEdNawraz Shawir, MBBS

APTR

Sharon Hull, MD, MPHPresident

Allison L. LewisExecutive Director

O. Kent Nordvig, MEdProject Representative

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Module 4: Screening

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