Sam G Campbell MB BCh, FCFP(EM), Dip PEC(SA), FCCHL. Chief, Department of Emergency Medicine Charles...
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Transcript of Sam G Campbell MB BCh, FCFP(EM), Dip PEC(SA), FCCHL. Chief, Department of Emergency Medicine Charles...
Of Hunters and Fishermen NSCFP Family Medicine Assembly
Peir 21, October 2, 2015
Sam G CampbellMB BCh, FCFP(EM), Dip PEC(SA), FCCHL.
Chief, Department of Emergency MedicineCharles V Keating Emergency and Trauma Centre
Professor of Emergency MedicineDalhousie University, Halifax, Nova Scotia.
Faculty: Sam Campbell
Relationships with commercial interests:◦ Grants/Research Support: Shire, NSHA, Boehringer-
Ingelheim.◦ Speakers Bureau/Honoraria: Boehringer-Ingelheim, ◦ Other: Employee PraxES Medical Group
Faculty/Presenter Disclosure
CFPC CoI Templates: Slide 1
This program has received no financial nor in kind support from anyone
Potential for conflict(s) of interest:◦ Sam Campbell has received no payment/funding,
from any organization whose product(s) are being discussed in this program.
Disclosure of Commercial Support
CFPC CoI Templates: Slide 2
Active involvement in Choosing Wisely Canada
Dal Critical thinking group
Mitigating Potential Bias
CFPC CoI Templates: Slide 3
Remind people about Choosing wisely Basic concept of testing
◦ Why/How tests lie ◦ How should we use them?
Clinical Context/Bayesian approach
Overview
P.H, 54 yr old ‘Check up’ CBC, ‘lytes, BUN/Creat, LFTs, Lipids, TSH, Fe,
PSA, Vit B12, folate, Vit D. Transaminases mildly elevated Repeat in a month (still up) Heaptitis serology, ANA, Abd US. 3.5 cm lesion in rt kidney (?angiomyolipoma) CT – confirms AML
Rational test ordering in family medicine
Can Fam Phys 2015;61:535-7.
Lab: US and CT: Missed work Anxiety ++ Reassurance???
Cost?
Can Fam Phys 2015;61:535-7.
L.A.W.
Canadian Journal of Diagnosis (in press)
What we do is not benign …
What we ask may not be either…….
Choosing Wisely Canada (CWC)
- campaign to help physicians and patients engage in conversations about unnecessary tests, treatments and procedures, and to help physicians and patients make smart and effective choices to ensure high-quality care.
Lists of interventions of questionable value from different specialist organizations.
1970 1980 1990 2000 2008 20110
2
4
6
8
10
12
14
16
18
GermanyU.K.CanadaJapanU.S.
OECD, 2013
Total health expenditures as % of GDP (1970-2011)
IOM - 30% of health care spending wasteful, no added value to patient care
Inappropriate testing◦ > 50% of prescriptions for respiratory infections◦ 28 - 65% of lumbar spine MRIs inappropriate◦ 9 - 16% of head scans for headache◦ Bone density scans, Vit D levels, pre-operative
tests………..
Issue of medical overuse
Hunters vs. Fishermen:
This is a simplistic preliminary discussion of a complicated issue
Doctors,
They are just tools, each designed for a purpose
Tests are not bad!
Test variability may be related to:◦ the test◦ the interpreter ◦ duration of symptoms/stage of the illness ◦ lab equipment, reagents, procedure, or even lab
error.
Test results should never be◦ accepted at face value◦ interpreted without considering pre-test (clinical)
probability of disease.
Medical tests are seldom useful unless taken in the appropriate clinical context
Diagnostic tests are used to:◦to help establish diagnoses.
Clinical uncertainty
◦ Culture ‘more is better’◦ Relieve pressure from patients/family (Cyberchondria)
◦ To delay making a decision (Entertain the patient while we wait for something to declare itself)
◦ Consultant expectations◦ Save time explaining/examining◦ Perpetuate the myth of medical clarity◦ “Routine”
Screening just because it is what we do!
Diagnostic tests are sometimes used to:
I’m going order this test because I don’t have time to tell you why you don’t need it…
Diagnosis◦ Rule In vs. Rule Out◦ Treatment Threshold
From a clinical perspective
Out of sight – ethereal/magical Measured once and rarely challenged
The Lab
Presumption that the result will help your patient
Presumption of benefit exceeding risk◦ Phlebotomy risks◦ Risk of false results◦ Waste of time/money◦ Misinformation/misinterpretation
It goes without saying..
Don't "make" diagnoses; they supplement clinical judgement and reduce the level of diagnostic uncertainty.
Unless applied and interpreted carefully, tests can be misleading.
Diagnostic tests:
The premise of diagnostic testing is that there are 2 populations of people ◦ those with the disease◦ those without .....
who differ on at least one testable parameter.
Almost all tests lie!
Most tests can be ‘positive’ for several reasons Not everyone with (for example) pneumonia
has an infiltrate on x-ray and not everyone with an infiltrate has pneumonia.
Patient variability and test variability result in an overlap between the results for diseased and normal populations for virtually all tests
The real world, however....
Most objective tests assess a measurable parameter and classify the patient as "normal" or "abnormal."
"Normal" is typically established by determining test values in disease-free people and identifying the range in which 95% of this population lies.
‘Normal’ values
Normal range of results
Uric acid levels in healthy and diseased patients.
There is variability in the normal and in the diseased population, and overlap between the two groups.
Some levels are therefore compatible with health or disease.
Imagine a test that screens people for a disease. ◦ Each person taking the test either has or does not
have the disease. ◦ The test outcome can be positive (predicting that
the person has the disease) or negative (predicting that the person does not have the disease).
◦ The test results for each subject may or may not match the subject's actual status – i.e. The test may lie
All tests can lie....... The trick is to
know when and why they lie....
True positive: Sick people correctly diagnosed as sick
False positive: Healthy people incorrectly identified as sick
True negative: Healthy people correctly identified as healthy
False negative: Sick people incorrectly identified as healthy
Each test will have it’s own strengths and weaknesses, and we can describe these.
All tests can lie.......
Sensitivity: the ability to recognize (rule in) the thing being tested for
Specificity: Precise – if it says the quality is present, then it is- able to rule out the thing being tested for
Test characteristics:
Population of mostly healthy people – your job is to find out who is sick
Population of mostly healthy people
Perfect test
A perfect test would be described as 100% sensitive (i.e. predicting all people from the sick group as sick)
and 100% specific (i.e. not predicting anyone from the healthy group as sick)
Sensitive test
Highly sensitive tests don’t miss those who
have a disease. The trade off is they will be positive in people who don’t. These are false positive results
Sensitive test
Specific test
Highly specific tests won’t be positive in
the absence of disease. The price? Some who have it will escape detection. These are false negatives
Specific test
Sensitivity and Specificity are not independent. When you increase one, you often decrease the other.
False negatives delay diagnoses. False positives create them.
All testing is susceptible to both
Good at one usually means bad at the other!
Test results are categorized as: ◦ True or false positive, or true or false negative
all relative to a ‘gold standard’ (which may also be imperfect..)
If that wasn’t vague/confusing enough…
Gold standard is more accurate, but too slow, expensive or invasive to do as a first line test.
The false positive rate is not just a function of sensitivity and specificity.
It is dependent on the actual risks an individual has of having the disease and how common the disease itself is.
Pre-Test Probability
Thomas Bayes (1701 –1761)
What do you need the test to do?
10% of patients with acute MI fail to develop ST segment changes.
20-30% of ST↑ have no MI
Electrocardiogram (ECG)
N Engl J Med 2003;349:2128-35
‘Screening’ ECG He has ST elevation Should we send him to hospital at once?
20 yr old football player...
‘Monitoring’ ECG completely normal Cancel the cath?
70 yr old smoker in acute pain.
In CCU admitted for acute ischemia and waiting for a cath.....
What do you need the test to do?
~80% of cases will have a high WBC WBC is ↑ in up to 70 % of patients with
other causes of right lower quadrant pain
Only including ‘grey zone’ cases, it may perform less well than clinical judgement!
White blood cell count in diagnosing appendicitis
Fig. 1: Hypothetical probability density distributions of measured plasma brain natriuretic peptide (BNP) levels in 2 subgroups of a study population.
Victor M. Montori et al. CMAJ 2005;173:385-390
©2005 by Canadian Medical Association
Fig. 2: These hypothetical probability density distributions reflect a study population of middle-aged patients who all have recurrent asthma and chronic CHF. The patients whose
dyspnea is caused by asthma exacerbations look clinically similar to those whos...
Victor M. Montori et al. CMAJ 2005;173:385-390
©2005 by Canadian Medical Association
Your clinical assessment is still critical!
LR+ 2-5 LR+ 5-10 LR+ >10
LR- 0.5-0.2 LR- 0.1-0.2 LR- <0.1
Small changes Moderate changes Large changes
Small changes Moderate changes
Large changes
Likelihood Ratios (LR)Likelihood of a positive test result in a patient with the target disorder compared that in a patient without the disorder LR+ = Sensitivity/1- Specificity
LR-+ 1-sensitivity/Specificity
Victor M. Montori et al. CMAJ 2005;173:385-390
©2005 by Canadian Medical Association
Likelihood Ratios
The ‘power’ of the test /Likelihood ratios depends on what you thought in the first place.
Radiation/blood loss Unnecessary intervention Inappropriate reasurrance Confirmation bias Cost
Why is this a big deal?
‘one third of health care costs could be saved without depriving any patient of beneficial care’ Howard Brody, 10.1056/nejmp0911423 nejm.org
when should we not order
tests?
• When it doesn’t matter: Seasonal viral illness Prostate screening in >80 Surgical conditions in people not fit for surgery Minor facial fractures
When not to do tests
When pre-test probability is really low:◦ Clinical picture◦ Rare conditions and no risk factors
Spinning a coin to rule out malaria is a really sensitive test in Tuktoyaktuk
When pre-test probability is so low that any positive is more likely to be false than true…..
If you already know the answer◦ Repeating normal screens too early◦ OA in older patients
When not to do tests
When risk of investigation/treatment approaches risk of illness◦ Contrast medium◦ Radiation
When not to do tests
When the test can’t answer the question you need answered◦ CT scan for cerebellar disease◦ Lumbar/cervical spine x-ray for ‘sprains’◦ Sinus x-rays
When not to do tests
When the evidence recommends against it! e.g. 'Ottawa rules’
Evidence-based guidelines suggest that: ◦ We should tailor screening to individual patient
health profiles and move to "opportunistic" screening
• We should screen only for conditions that: Cause serious illness or functional difficulties, and only when an accurate test and effective treatments
are available.
http://www.cfhi-fcass.ca/publicationsandresources/Mythbusters/
Cadman D et al. JAMA 1984;251: 1580-1585.
Screening:
Forcing function: we should ask ourselves BEFORE ordering a test:
• What will I do if the result is •+ve?•-ve?
• Will it improve the management of my patient?• What is the benefit related to the cost?
Or,
Ask yourself if you are being…
‘I’m going to do a test to supplement my clinical impression’
‘I’ll just do all of the tests and see what you might have’
Discussion:
26 yr old female Dysuria, frequency, suprapubic discomfort Afebrile, no back pain, N/V. Has had previous UTI’s – pretty much the
same..
Our options:◦ Urine dip?◦ Microscopy?◦ Culture?◦ Empiric treatment?◦ Treat only if Positive test?
Example: Urinary tract Symptoms
Four symptoms and 1 sign increased the probability of UTI:◦ dysuria LR, 1.5 ◦ frequency LR, 1.8◦ hematuria LR, 2.0◦ back pain LR, 1.6◦ costovertebral angle tenderness LR, 1.7
Four symptoms and 1 sign decreased the probability of UTI: ◦ absence of dysuria negative LR, 0.5; ◦ absence of back pain NLR, 0.8; ◦ history of vaginal discharge NLR, 0.3◦ history of vaginal irritation NLR, 0.2◦ vaginal discharge on examination NLR, 0.7
Review in JAMA of the value of Hx and Physical exam to investigate UTI..
JAMA. 2002 May 22-29;287(20):2701-10.
2 most powerful signs/symptoms - history of vaginal discharge and history of vaginal irritation◦ Neg LR of UTI when present (LRs, 0.3 and 0.2,
respectively).
Using combinations of symptoms:◦ LRs 24.6 for the combination of dysuria and
frequency but no vaginal discharge or irritation.◦ In patients with recurrent UTI one study found
that self-diagnosis significantly increased the probability of UTI (LR, 4.0).
JAMA. 2002 May 22-29;287(20):2701-10.
Reasonable to rule in infection, but not better that clinical judgement.
Not good enough to rule it out.◦ 57-96% sensitive and 94-98% specific for
identifying pyuria
What about urine dip?
Emerg Med J. 2003 Jul;20(4):362-3. Am J Med. 2002 Jul 8;113 Suppl 1A:20S-28S.
Ann Emerg Med. 1989 May;18(5):560-3.
◦ In women who present with >1 symptoms of UTI, the probability of infection is ~ 50% Physical exam, and tests are not able to lower the
post-test probability to a level where a UTI can be ruled out
◦ Specific combinations of symptoms raise the probability to >90%, effectively ruling in the diagnosis based on history alone.
CONCLUSION (UTI):
JAMA. 2002 May 22-29;287(20):2701-10.