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Teaching EBLM: How to spread
the word?
Robert H. Christenson, Ph.D., DABCC, FACB
Professor of Pathology
Professor of Medical & Research Technology
University of Maryland School of Medicine
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Evidence-Based Medicine (EBM)
Use of strongest available data to
make informed, unbiased,
decisions about the diagnosis
and treatment of patients.
(JAMA 1992:268;2420.)
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Evidence-Based Medicine
“……trying to improve the quality of
the information on which decisions
are based.”
Glasziou et al 2003
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Evidence-Based Medicine:
Clinical versus Laboratory
Clinical EBM Questions:
Treatment and Intervention
Versus
Evidence Based Laboratory
Medicine (EBLM) Questions:
Information
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Evidence-Based (Laboratory)
Medicine Process
Clinical or Policy Problems
ASK
ASSESS
APPLY
A5
Cycle
ACQUIRE
APPRAISE
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ASK the Question
Most Important Aspect
Of EBM or EBLM
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Types of Clinical Questions
• Screen for disease
• Rule-in diagnosis
• Rule-out diagnosis
• Assess prognosis
• Start intervention or treatment
• Adjust intervention or treatment
• Stop intervention or treatment
• Assess efficacy
• Assess compliance
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Formulate an Answerable Question
the PICO system
• Population/patient
• Indicator/intervention/test
• Comparator/control
• Outcome
• Setting
• Timing
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Formulate an Answerable Question
B-type Natriuretic Peptide (BNP) in Urgent Care
Can I use the plasma BNP test
to rule-in or rule-out
decompensated heart failure in
patients presenting with
dyspnea to urgent care?
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Formulate an Answerable Question
BNP in Urgent Care
Can I use the plasma BNP test (I) to
rule-in or rule-out (O) decompensated
heart failure in patients presenting with
dyspnea (P) to urgent care (S)?
Comparison: gold standard
diagnosis
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ACQUIRE the Information
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APPRAISE the Information
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Quantitative Effects of Study Characteristics
on Estimates of Diagnostic Accuracy
Study Characteristic
Relative Diagnostic
Odds Ratio
(95% Confidence Interval)
Spectrum bias
Differential verification
Partial verification
No blinding
Selection bias
Retrospective design
Absence test description
No population description
No reference standard
description
Relative Diagnostic Odds Ratio (95% Confidence Interval)
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Lijmer J. et al. JAMA 1999; 282:1061-1066
Spreading the Word
• Teaching must be focused on learners’ needs.
• Be prepared to discuss the context of EBLM.
• Address any anxiety about acquiring the skills needed to
use EBLM
• Learning needs to be connected to how EBLM will be used
in practice.
• Learning needs to balance passive versus active methods.
• Be alert for teachable moments.
• Seek feedback and evaluation of your performance as a
teacher.
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Teaching must be focused
on learners’ needs.
Learning needs to be
connected to how EBLM
will be used in practice.
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Expression for
Bayes theorem is:
Posttest odds = Pretest odds X likelihood ratio
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Probability vs. Odds
Probability: Likelihood
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25
= 0.25
75
75
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Odds: Odds Ratio
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= 0.333
Humans are used
To thinking in probabilities
rather than odds
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The Clinical Process
History and physical exam
Determines
Pretest probability
Guides
Choice of
Diagnostic studies
Post Test Probability
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Fagan’s Diagram
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BNP in Urgent Care
Plasma BNP is measured to
rule-in or rule-out
decompensated heart failure in
70 year-old dyspnea patient
presenting to urgent care.
BNP value is 125 ng/mL
Does this patient have DHF?
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ROC CURVE ANALYSIS
N Engl J Med 2002;347:161-167.
N = 1586
1.0
BNP = 50 (pg/ml)
BNP = 80 (pg/ml)
Sensitivity
0.8
BNP = 100 (pg/ml)
BNP = 125 (pg/ml)
BNP = 150 (pg/ml)
0.6
AUC = 0.91 (0.90-0.93)
0.4
0.2
0.0
0.0
0.2
0.4
0.6
0.8
1.0
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1-Specificity
Rapid measurement of BNP in the Emergency
Diagnosis of Heart Failure
Engl J Med 2002;347:161-167.
N = 1586
Heart
Failure
744
Not Heart
Failure
770
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Pretest probability = 50%
History of LV
Dysfunction
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(Dyspnea due to Non-Cardiac Cause)
ROC CURVE ANALYSIS
N Engl J Med 2002;347:161-167.
N = 1586
1.0
BNP = 50 (pg/ml)
BNP = 80 (pg/ml)
Sensitivity
0.8
BNP = 100 (pg/ml)
BNP = 125 (pg/ml)
BNP = 150 (pg/ml)
0.6
AUC = 0.91 (0.90-0.93)
0.4
Sensitivity
0.2
0.85
+LR = ------------------------ = --------- =
(1 – Specificity)
0.22
3.9
0.0
0.0
0.2
0.4
0.6
1-Specificity
0.8
1.0
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Fagan’s Diagram
PostTest = 0.80
PreTest = 0.50
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ROC CURVE ANALYSIS
N Engl J Med 2002;347:161-167.
N = 1586
If BNP=1000
1.0
BNP = 50 (pg/ml)
BNP = 80 (pg/ml)
Sensitivity
0.8
BNP = 100 (pg/ml)
BNP = 125 (pg/ml)
BNP = 150 (pg/ml)
0.6
AUC = 0.91 (0.90-0.93)
0.4
Sensitivity
0.2
0.60
+LR = ------------------------ = --------- = 12
(1 – Specificity)
0.05
0.0
0.0
0.2
0.4
0.6
1-Specificity
0.8
1.0
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Fagan’s Diagram
PostTest = 0.93
PreTest = 0.50
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Probability of Diagnosis
0%
Treatment
Threshold
Test
Threshold
100%
Probability below
test threshold:
no testing warranted
Probability above treatment
threshold; testing completed;
treatment commences
Probability between test
and treatment threshold:
further testing required
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Who enrolled in the BNP Study?
Pre-test likelihood of Disease
No renal insufficiency (creatinine <1.5 mg/dL)
47%
28%
25%
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McCullough et al. Circulation 2002;106:416
ROC Curves Lower by 15% in General Use
0.75
1.00
Moons KG, Donders AR, Steyerberg EW, Harrell FE. Penalized maximum
likelihood estimation to directly adjust diagnostic and prognostic prediction models
for overoptimism: a clinical example. J Clin Epidemiol 2004;57(12):1262-70.
Sensitivity
0.50
150 pg/mL
0.25
Sensitivity
0.75
0.00
+LR = ------------------------ = --------- = 2.0
(1 – Specificity)
0.35
0.00
0.25
0.50
1 - Specificity
0.75
1.00
ROC Curve Area =0.74
95% Confidence Interval = (0.69, 0.76)
From: Clin Chem. 2007;53:1511-9.
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Fagan’s Diagram
PostTest = 0.64
PreTest = 0.50
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BNP in Urgent Care
Plasma BNP is measured to
rule-in or rule-out
decompensated heart failure in
70 year-old dyspnea patients
presenting to urgent care.
BNP value is 150 ng/mL
Does this patient have DHF?
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How to spread the word?
•
•
•
•
•
Teach to the needs of the students (audience).
Project excitement about the topic
Look for (or create) teachable moments.
Use practical examples.
Learning needs to balance passive versus
active methods.
It all starts with the clinical question (PICO).
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Grazie Mille!
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