Download Utilizing Biostatistics in Diagnosis, Screening, and Prevention 2013

Utilizing Biostatistics in Diagnosis,
Screening, and Prevention
2013-2014 • Presentation 3 of 6
Learning Objectives
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Review important statistical concepts and understand how to apply them to
support high value care decisions when considering diagnostic and screening tests
and proposed treatments
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Define the four categories of preventive care
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Explore the benefits and harms (including cost) of routine screening
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Use electronic tools to identify preventive measures that will provide high value
for your patients
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Examine the evidence supporting your recommendations
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Develop an approach to customize preventive care recommendations to an
individual patient and his/her unique risk factors, values, and concerns
Essential Biostatistical Concepts
Pretest and Posttest probability
Disease
Positive
Disease
Negative
Test
Positive
a
b
Test
Negative
c
d
Sensitivity and Specificity
Positive/Negative Predictive Values
Likelihood Ratios
Number Needed to Treat/Harm
Likelihood Ratios
Using likelihood ratios:
1. Use the estimated pretest probability
of disease as an anchor on the left side
of the graph
2. Draw a straight line through the known
likelihood ratio, either (+) or (-)
3. Where this line intersects the graph on
the right represents the posttest
probability of disease
Role of Diagnostic Tests
• To reduce uncertainty regarding a specific patient’s diagnosis
• Generally most appropriate for patients you feel have an intermediate
(10-90%) pre-test probability of a disease (Ex. Centor criteria for Strep
pharyngitis)
• Test characteristics (i.e. likelihood ratios) should be considered before
ordering a test to help determine whether a given test would significantly
alter your pre-test probability (and thus affect management)
(Ex. if you estimate a patient’s pretest probability to be 10% but the LR of
a diagnostic test is only 2, then a positive test result will still only yield
around a 25% posttest probability )
Approach To Chest Pain: Small Group Exercise
• Break into 3 small groups
• Each group will work through a different case of chest pain
• Focus on the diagnostic process:
• Estimating the pretest probability of disease in your patient
• Evaluate how cardiac stress testing in your patient would influence your
pretest probability of disease
• Assess whether you believe that cardiac stress testing would be helpful
in your patient
• Be prepared to briefly summarize your findings and share them
with the larger group
Preventive Practice:
The Periodic Health Examination
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A 57-year-old woman presents for her periodic health
examination. She has not been seen by a doctor for
ten years
She has no past medical history except for a hysterectomy
for fibroids 10 years ago. She takes no medications
She is a retired teacher, lives alone, smokes 1 pack per day
(38 pack years), does not use alcohol or illicit drugs, and has
not been sexually active since her husband died 8 yrs ago
She has no family history of cancer, vascular disease, or
osteoporosis
Her BP 135/83 and her BMI is 24, the remainder of her
exam is unremarkable
What Should be Included in her
Preventive Care?
• Rank the top five preventive services
you might offer this patient. Use the
categories below to help you.
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Immunizations
Screening
Behavioral counseling to motivate lifestyle
changes
Chemoprevention
Preventive Care Menu
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Influenza vaccine
Pneumococcal vaccine
Td/TDAP
Zoster vaccine
Smoking cessation
Weight loss
Exercise
Alcohol misuse
Aspirin
Statin therapy
Hepatitis C screening
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Calcium/Vitamin D
Tamoxifen
Mammogram
Colonoscopy
Pap smear
HIV screening
Lung cancer screening (LDCT)
DEXA scan
HbA1C
Fasting lipid panel
Domestic violence screening
Role of Screening Tests
• To detect asymptomatic and early stage disease
• Should be highly sensitive and highly specific to pick up
most cases of true disease and avoid false positives
• Targeted toward populations with a higher disease
prevalence (high positive predictive value)
• Should be relatively safe and cost-effective
• Should screen for diseases in which early identification
and treatment have been demonstrated to improve
clinical outcomes
Cost-effectiveness
1
“Cost-saving”
Reduces cost,
Improves health
Costs money,
Improves health
Costs money,
Worsens health
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Measures that cost money but improve health can be further categorized by their cost,
often measured in dollars per QALY (quality-adjusted life-year)
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QALYs incorporate an estimate of the quantity of life gained by the intervention, coupled with
a more subjective assessment of the quality of that life affected by the intervention
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Historically, payers have considered any intervention that has a cost-effectiveness ratio of
<$100K per QALY as acceptable
Cohen J, Neumann P, Weinstein M NEJM 2008:358;72
Common Harms Associated with Screening
False positive results
• Can lead to incorrect
labeling, inconvenience,
expense, and physical
harm in follow-up tests
“Overdiagnosis3” and
“Pseudodisease”
(Length-time bias)
USPSTF Recommendation Grades, Electronic Preventive
Services Selector (ePSS), and Vaccine Scheduler
• USPSTF provides a tool for clinicians (ePSS) to search for graded
recommendations.
epss.ahrq.gov/PDA/index.jsp
• Vaccine recommendations are available in the second tool.
www.cdc.gov/vaccines/schedules/Schedulers/adult-scheduler.html
• The ACP also offers a downloadable Immunization Advisor,
listed below.
immunization.acponline.org/app/
USPSTF Recommendation Grades
Grade
Definition
A
The USPSTF recommends the service. There is high certainty that the net benefit is substantial.
B
The 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.
C
Note: The following statement is undergoing revision.
Clinicians may provide this service to selected patients depending on individual circumstances. However, for most
individuals without signs or symptoms there is likely to be only a small benefit from this service.
D
The USPSTF recommends against the service. There is moderate or high certainty that the
service has no net benefit or that the harms outweigh the benefits.
I Statement
The USPSTF concludes that current evidence is insufficient to assess the balance of benefits & harms of the service.
Lets Plug our Patient into the ePSS Calculator
epss.ahrq.gov/PDA/index.jsp
Compare your top 5 to their top five:
1. Aspirin for chemoprevention of CVD – grade
A
2. Colorectal cancer screening – grade A
3. Lipid screening- grade A
4. Tobacco use counseling and intervention –
grade A
5. Combined influenza/pneumococcal vaccine
(not in calculator)
Balancing Benefits and Harms
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Daily ASA use results in a 17% absolute risk reduction in ischemic CVA for women
and 32% absolute risk reduction for MI in men
Major risk of daily ASA use is serious upper GI bleed
Both the risk of major GI bleed (net harm) and the risk of ischemic CVA (net
benefit) increase with age
Using data from large randomized controlled trials, USPSTF has provided tables
that estimate the absolute # of strokes and MI prevented per 1000 women and
men, respectively, stratified by baseline stroke risk and age
Baseline 10-yr CVA risk can be calculated using:
www.westernstroke.org/PersonalStrokeRisk1.xls
= 3.5% for our patient
Balancing benefits and harms
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What about for this patient?
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Mr. T is a 50 yo male who comes to your office for routine follow-up
He has heard that taking an aspirin may decrease his risk of a heart attack and is
wondering whether he should start taking daily aspirin
Past medical history
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No family history of CAD
No personal history of CAD or gastrointestinal issues
His only medical history of HTN, well controlled with medication
His recent lipid profile shows total cholesterol of 160, HDL 50
PE in office with normal cardiac and general exam, BP 110/74
How would you counsel him? What is the data?
Use Framingham risk assessment calculator (10 yr MI risk) at
hp2010.nhlbihin.net/atpiii/calculator.asp = 2%
Summary
• Diagnostic tests should only be used if the result is likely to
significantly affect your certainty of a disease (posttest probability)
and should rely on likelihood ratios for a given test when available
• Preventive healthcare must be individualized with the help of
expert recommendations (USPSTF) to offer patients interventions
that are most likely to positively impact their long-term healthcare
goals
• Recommendations are not prescriptive, but rather the beginning of
an open dialogue with patients to create (as a team) a prioritized
plan of preventive health maintenance
Commitment in your Practice
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Think about your approach to diagnostic and
screening tests
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Do you routinely make recommendations that are
not in line with the high value principles outlined in
this module?
Write down at least one thing to Start doing and one
thing to Stop doing
START:
STOP:
References
1. Owens D, et al. High-value, cost-conscious health care: concepts for clinicians to
evaluate the benefits harms and costs of medical interventions. Ann Intern Med.
2011; 154: 174-80
2. Cohen JT, et al. Does preventive care save money? Health economics and the
presidential candidates. N Engl J Med. 2008; 358:661-3.
3. Moynihan R, et al. Preventing overdiagnosis: how to stop harming the healthy.
BMJ. 2012; 344: e3502.
4. U.S. Preventive Services Task Force; Aspirin for the Prevention of Cardiovascular
Disease: U.S. Preventive Services Task Force Recommendation Statement. Annals
of Internal Medicine. 2009 Mar;150(6):396-404.