Bai 5: CHUNG CU CUA CAC NGHIÊN CƯU CHAN DOAN
Matthew J Thompson
GP & Senior Clinical Scientist
<, Department of Primary Health Care
Trang 2Nội dung bài học
=» Cơ sở chân đoán
Trang 4acl hệt các sai lâm trong chân đoán là
ognitive errors:
Conditions of uncertainty
Thinking is pressured Shortcuts are used
(Ann Croskerry Ann Emerg Med 2003)
Những sai lâm trong chan ¢ doan (Diagnostic errors -
The next frontier for Patient Safety Newman- -Toker, JAMA 2009)
airport US hospital deaths from
misdiagnosis per year
Adverse events, negligence cases, serious disability more II ikely to be related to
Trang 5Diagnostic strategies particularly important
where patients present with variety of conditions
and possible diagnoses
Trang 6Thi du: nguyén nhan cua ho la gi?
Comprehensive history —~ examination —— differential diagnosis —— final diagnosis
`
Coagralulafieas,
iE only took you
Trang 7Congratulations, i€ only took you 65299 seconds For example, what causes cougn? Comprehensive history examination diagnosis final diagnosis
Cardiac failure, left sided , Chronic obstructive pulmonary disease , Lung abscess Pulmonary alveolar proteinosis, VWWegener's granulomatosis, Bronchiectasis Pneumonia, Atypical pneumonia, Pulmonary hypertension
Measles, Oropharyngeal cancer, Goodpasture's syndrome
Pulmonary oedema, Pulmonary embolism, Mycobacterium tuberculosis
Foreign body in respiratory tract, Diffuse panbronchiolitis, Bronchogenic carcinoma Broncholithiasis, Pulmonary fibrosis, Pneumocystis carinii
Captopril, Whooping cough, Fasciola hepatica
Gastroesophageal reflux, Schistosoma haematobium, Visceral leishmaniasis Enalapril, Pharyngeal pouch, Suppurative otitis media
Upper respiratory tract infection, Arnold's nerve cough syndrome, Allergic bronchopulmonary aspergillosis Chlorine gas, Amyloidosis, Cyclophosphamide
Tropical pulmonary eosinophilia, Simple pulmonary eosinophilia, Sulphur dioxide Tracheolaryngobronchitis, Extrinsic allergic alveolitis, Laryngitis
Fibrosing alveolitis, cryptogenic, Toluene di-isocyanate, Coal worker's pneumoconiosis Lisinopril, Functional disorders, Nitrogen dioxide, Fentany!
Asthma, Omapatrilat, Sinusitis Gabapentin, Cilazapril
Trang 10Validity of diagnostic studies
1 Was an appropriate spectrum of patients included?
2 Were all patients subjected to the gold standard’?
Trang 121 Was an appropriate spectrum of
patients included?
You want to find out how good chest X rays are for diagnosing pneumonia in the Emergency Department
Best = all patients presenting with
difficulty breathing get a chest X-ray
Spectrum bias = only those patients in
whom you really suspect pneumonia get a
Trang 142 Were all patients subjected to the gold Standard?
You want to find out how good Is exercise ECG (‘treadmill test’) for identifying patients with angina
The gold standard is angiography Best = all patients get angiography
Verification (work-up bias) = only patients who have a positive exercise ECG get
Trang 163 Was there an independent, blind or objective comparison with the gold
standard’? Observer bias
You want to find out how good Is exercise ECG for identifying patients with angina All patients get the gold standard
(angiography)
Trang 18Differential Reference Bias
| |
RUN ID Ref Std B
Trang 19Were all patients subjected to the Gold
Standard?
Trang 20Go SN
Appraising diagnostic tests '®:
1 Are the results valid?
2 What are the results? mm
3 WIlI they help me
Trang 252 by 2 table: sensitivity Disease + _ cv Sensitivity =a/a+c Proportion of people with the disease who
have a positive test result
a highly sensitive test will not miss many
Trang 272 by 2 table: specificity
Disease
+ Proportion of people
without the disease
who have a negative
f{es{ result
Trang 28
= Sensitivity is useful to me
= Specificity isnt | want to know about the
false positives
Trang 31Your father went to his doctor and was told that his test for a disease was positive He is really
worried, and comes to ask you for help!
After doing some reading, you find that for men
of his age:
The prevalence of the disease is 30%
The test has sensitivity of 50% and specificity of 90%
“Son, tell me what’s the chance
Trang 34Try tt again = A disease with a prevalence of 4% must be diagnosed a It has a sensitivity of 50% and a specificity of 90%
Trang 36Doctors with an average of 14 yrs experience
answers ranged from 1% to 99%
half of them estimating the probability as 50%
Trang 37Sensitivity and specificity don't vary
with prevalence
= Test performance can vary in different settings/
patient groups, etc
= Occasionally attributed to differences in disease
Trang 382 xX 2 table: positive predictive value Disease + _ cv PPVE=a/a+b Proportion of people
with a positive test who have the disease
Trang 39
2 X 2 table: negative predictive value Disease + b Proportion of people
with a neøafive tesf
Trang 40What’s wrong with PPV and TY
Trang 422 X 2 table: positive likelinood ratio
How much more often a positive test occurs in people with
Trang 432 X 2 table: negative likelinood ratio
Disease How less likely a negafive Ray
KT result is in people with the
Trang 45APPENDICITIS Probability ot decrease increase Fs -45% -30% -15% +15% +30% +45% 0.1 0.2 0.5 1 2 5 10 | "` OO
Absence of severe right lower McBurney's point tenderness
quadrant tenderness Rovsing's sign
Trang 46reasoning Pre test 5% Fagan 7 A )
Pretest Likelihood Post-test nomogram
Trang 47—
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ess |) http://www.cebm.net; w| Links ” ^ Sean CATmaker
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TAME 2 OL\Ir diagnosis TARGET DISORDER Analysis 1 of 1 Present Absent Welcome to CEBM
¥velcome to the web site of Centre for Evidence-Based in Oxford in the UK TEST to apply for bursary Teaching Evidence e Workshop, Oxford b 95% Confidence Intervals d
Our broad aim is to develop SENSITIVITY Y
and promote evidence-bas care and provide supporta
resources to doctors and h Pre-test %% ch - research reviews sed Views - latest blog ew EBM tool
LIKELIHOOD RATIO + sens / (1 - LIKELIHOOD RATIO - (1 - sens) /
care professionals to help the highest standards of m Heh FOP Srey 2 CE Nady Pe LAL EO another test in this same show formulae
Please enter the numbers in each group for the diagnostic testin the study VWhen you're ready, click the
CALC button to work out Sensitivity, Specificity, Likelinood Ratios, etc
Learn more about EBM and mu ý
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Cind ait mara
Trang 48ourvey of 300 US physicians
8 used Bayesian methods, 3 used
ROC curves, 2 used LRs
VWVhy?
Indices unavailable lack of training
not relevant to setting/population
other factors more important
(Reid et al Academic calculations versus clinical judgements: practicing physicians’ use of
Trang 49Go SN Appraising diagnostic tests '®: 1 Are the results valid? 2 What are the resul(s 2
3 Will they help me
look after my patients?
Trang 50
Reproducibility of the test and interpretation in my setting
Jo results apply to the mix of patients | see?
Will the results change my management?