Transcript Slide 1

Rational Clinical Exam
Does This Patient Have….?
Sharon E. Straus MD MSc FRCPC
St. Michael’s Hospital
University of Toronto
Competing interests
Co-editor of the RCP Series, JAMA
 I do not receive royalties from the RCE
book
 No pharma/industry funding
 Editor for ACP Journal Club, EBMJ, CMAJ
 Editorial Boards for J Clinical
Epidemiology, BMJ

Objectives
To enhance our ability to seek and apply
evidence about diagnostic decision
making
 To enhance our ability to use the Rational
Clinical Exam series in diagnostic decision
making
 To reinforce that likelihood ratios can be
fun

Uses of the Clinical Examination
1.
To make a diagnosis
Of all the diagnoses ever achieved
In General Internal Medicine:
73% are made by the end of the
examination
Sandler G. Am Heart J 1980;100:928-31
Uses of the Clinical Examination
2.
3.
4.
5.
6.
7.
To screen and case/find
To determine prognosis/severity
To start and stop investigations
To monitor and modify treatment
To develop rapport
To occupy the patient while we think
But, the clinical exam may be
less helpful in different settings
When 10 and 20 clinicians refer patients
with positive signs/symptoms, the
diagnostic values of these symptoms and
signs are ‘used up’ along the way
(specificity usually falls)
 As a result, 20 and 30 clinicians tend to
proceed quickly to the ‘definitive
investigation’ (DI)

Why not ignore the exam and
proceed directly to the ‘DI’?
DIs are only available to a small fraction of
patients world-wide
 Opportunity costs of DIs are high in most
settings and often prohibitive
 Interpretations of DIs depend on the
clinical examination (and the exam can
sometimes tell us whether to believe the
DI!)

The probability that a patient has a DVT can be
determined from 9 items on the clinical exam
For patients with scores 0 or neg:
3%
(in these people we shouldn’t believe a positive
compression ultrasound)
 For patients with scores 1-2:
17%
 For patients with scores  3:
75%
(in these patients we shouldn’t believe a negative
compression ultrasound)

Wells et al. Lancet 1997;350:1795-8.
And, definitive investigations
aren’t always definitive

Review of the reliability of expert
histopathologists whose conclusions are used
for:

making prognoses (based on invasiveness in
melanoma)
 major treatment decisions (based on grading breast
cancer, or reporting the presence of interface
hepatitis)

Reported the probability (beyond chance) that
expert pathologists agree
Reporting the probability that
examiners agree:
Using the kappa statistic:
 k < 40%
poor agreement
 k 40 to 60% fair
 k 60 to 80% moderate
 k 80%
almost perfect agreement

Probability that 2 pathologists
agree:

About the degree of invasion of a
melanoma:
 23-68%

About the grade of a breast cancer:
 18-36%

(poor-moderate)
(poor)
About whether a liver biopsy has
piecemeal necrosis:
 20%
(poor)
What is the Rational Clinical
Exam?
1991- Dave Sackett proposed the idea of
the RCE at the SGIM meeting
 Emphasis then, and now, was in getting
junior clinicians involved
 Aim is to sort out what is useful from what
is useless in the history and physical
examination

Rational Clinical Exam

82 articles
 Holroyd-Leduc
JM, Tannenbaum C, Thorpe
KE, Straus SE. What type of urinary
incontinence does this woman have? JAMA
2008;299:1446-56.

Book published in August 2008
Does this patient have ascites?




Patient 1
 44 year old man with cirrhosis admitted with fever and no
obvious source of infection.
Patient 2
 57 year old woman with an adnexal mass and recent weight gain
but otherwise feels well.
What is the pretest probability of ascites in
 Patient 1?
 Patient 2?
What other information on history and physical would help you to
rule in or rule out ascites?

JAMA 1992;267:2645-8.
Probability of Disease (0 to 100%)
Stem and Leaf Plot: Patient 1
10
9
8
7
6
5
4
3
2
1
0
Probability of Disease (0 to 100%)
Stem and Leaf Plot: Patient 2
10
9
8
7
6
5
4
3
2
1
0
What is the pretest probability?


Prevalence: the probability of disease before we
apply a screening test, in this case the clinical
examination
We can find this information:
 In
studies of test accuracy or differential diagnosis
 From audits in our own setting or settings similar to
ours
 From our own practice
What other information would be useful in ruling in
or ruling out the diagnosis of ascites?
Patient 1

44 year old man with cirrhosis admitted
with fever and no obvious source of
infection
 Pretest
probability of ascites 60%
 Fluid wave detected on physical exam

Likelihood ratio 6 (95% CI 3.3 to 11.1)
What is a likelihood ratio and how
do we use it???
It’s a tool that takes us from a pretest
probability to a post test probability
 It’s determined for a particular test result
 It refers to how much more likely (LR>1) or
less likely (LR <1) the disease is, given the
particular test result
 It’s a numerator/denominator

LR: impact on likelihood of disease
0
Increasing impa
ct
increasi
LR = 1
No
Impact on
Likelihood
of Disease
ng impact

LR: impact on likelihood of disease
LR=.01
LR=100
LR =.1
Less
Likely
0
Less
LR=10
LR =.2
Less
LR = 5
LR = .3
LR = 3
Likely
Likely
Less
More
Likely
Likely
Increasing impa
ct
increasi
LR = 1
No
Impact on
Likelihood
of Disease
More
More
Likely
Likely
More
Likely
ng impact

Patient 1

44 year old man with cirrhosis admitted
with fever and no obvious source of
infection
 Pretest
probability of ascites 60%
 Fluid wave detected on physical exam

Likelihood ratio 6 (95% CI 3.3 to 11.1)
 What
is the post test probability of
ascites?
Nomogram for interpreting LR



Ref: JAMA Mar 2, 1994; 271(9):703-7
Plot patient’s pretest
probability on left
Draw straight line
through LR for given
test result
Line points to posttest probability
Patient 2

57 year old woman with an adnexal mass
and recent weight gain but otherwise feels
well.
 Pretest
probability 20%
 No ankle swelling on history

LR 0.10
 What
is the post test probability of
ascites?
Nomogram for interpreting LR



Ref: JAMA Mar 2, 1994; 271(9):703-7
Plot patient’s pretest
probability on left
Draw straight line
through LR for given
test result
Line points to posttest probability
Patient 1

44 year old cirrhotic man with fever, and
ascites
 Does
this patient have spontaneous
bacterial peritonitis?
Rational Clinical Procedures
How do we perform these procedures to
improve diagnostic yield and decrease risk
of adverse events?
 How do we analyse the results of this test?
 How can this procedure be taught?

How do we perform the procedure?

Literature search retrieved 1676 articles of which 17 met
the inclusion criteria and were included in the analysis



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Preprocedure coagulation studies: 2 studies
Location of paracentesis/ultrasound guidance: 3 studies
Needle design: 1 study
Bedside inoculation

For every 5 patients who have ascitic fluid immediately inoculated
into a bedside culture bottle vs. delayed inoculation by the lab, 1
additional patient with bacterial infection will be detected

Wong C, Holroyd-Leduc J, Thorpe K, Straus SE. How do I perform
a paracentesis and analyse the results? JAMA 2008;299;1166-78.
How do we analyse the results of
this test?

Literature search retrieved more than 780 studies of which 20 were included
Lab Test
Summary +LR (95% CI)
WBC >1000 cells/µl
9.1 (5.5 to 15.0)
PMN > 250 cells/µl
6.4 (4.6 to 8.8)
pH < 7.35
9.0 (2.0 to 41.0)
Blood-ascitic fluid pH
gradient
11 (4.3 to 30.0)
Patient 1

44 year old cirrhotic man with fever, and
ascites
 Does
this patient have spontaneous bacterial
peritonitis?
 Pretest probability 30%
 PMN count from ascitic fluid 623

LR is 6.4 (4.6 to 8.8)
 What
is his post test probability of SBP?
Where do we find information about
the clinical examination?

What resources are freely available?
Summary
The clinical examination and the RCE
have a role outside of the Royal College
Exam
 Likelihood ratios can be fun!
 Some final thoughts on learning:

Advice on the importance of learning from TH White in the
Once and Future King:

‘The best thing for being sad is to learn something. That
is the only thing that never fails. You may grow old and
trembling in your anatomies, you may lie awake at night
listening to the disorder of your veins, you may miss your
only love, you may see the world about you devastated
by evil lunatics, or know your honour trampled in the
sewers of baser minds. There is only one thing for it
then—to learn. Learn why the world wags and what
wags it. This is the only thing which the mind can never
exhaust, never alienate, never be tortured by, never fear
or distrust, and never dream of regretting.’
Acknowledgements
To the people that I learn from:
 The amazing residents, fellows and
graduate students with whom I am
privileged to work
