role of diagnostic test-osman sianipar-ce and bu-clinical pathology (2015)
DESCRIPTION
Role of Diagnostic Test-Osman Sianipar-CE and BU-Clinical Pathology (2015)TRANSCRIPT
-
Osman SianiparClinical Epidemiology & Biostatistics Unit
Department of Clinical PathologySchool of Medicine University of Gadjah Mada/Dr Sardjito Hospital
20/03/2015 1Role of Diagnostic test
-
A 60-year old man came to the mergency department complaining of cough and fever lasting several weeks. He reported night sweats and wight loss over the last few months. He admitted to drinking alcohol heavily on weekends and to staying in a homeless shelter. The patient had a fever and appeared very thin. He coughed frequently during examination.
Question: What is differential diagnosis? What other examination should be requested?
20/03/2015Role of Diagnostic test 2
-
Anamnesis
Physical examination
Additional tests
Treatment
Radiology
Lab Medicine
Electro medics
Other tests
20/03/2015 3Role of Diagnostic test
-
To rule in
To rule out
To screen
Diagnosis
To monitore the treatment
20/03/2015 4Role of Diagnostic test
-
precise but
not accurate
Accurate but
not preciseAccurate and precise
20/03/2015 5Role of Diagnostic test
-
Accurate Not accurate
Precise
Not precise
20/03/2015 6Role of Diagnostic test
-
20/03/2015Role of Diagnostic test 7
Interval
Ratio
Ordinal
Nominal
-
Accuracy Precision
Sensitivity
Specificity
Positive predictive value
Negative predictive value
Likelihood ratio
Unweightedkappa index
20/03/2015Role of Diagnostic test 8
-
20/03/2015Role of Diagnostic test 9
+ -
+
Disease
T
e
s
t
True
positive
False
positive
False
negative
True
negative-
-
20/03/2015Role of Diagnostic test 10
Sensitivity = a / (a+c)
Specificity = d / (b+d)
Accuracy = (a+d) / N
+ PV = a / (a+b)
- PV = d/ (c+d)
Prevalence = (a+c) / N
+ -
+
Gold Standard
Test
result
a b
c d-
a+b
c+d
a+c b+d N
-
20/03/2015Role of Diagnostic test 11
Sensitivity: proportion of test positive result
among diseased group
Specificity: proportion of test negative result
among non diseased group
Positive PV: probability of having a disease of
a patient who has positive test result
Negative PV: probability of having no disease
of a patient who has negative test result
-
20/03/2015Role of Diagnostic test 12
Likelihood ratio positive: ratio of
positive test result in diseased group
as compared to non diseased group
Likelihood ratio negative: ratio of
negative test result in diseased group
as compared to non diseased group
-
20/03/2015Role of Diagnostic test 13
a/a+c
LR (+) = --------
b/b+d
c/a+c
LR (-) = --------
d/b+d
+ -
+
Gold Standard
Test
result
a b
c d-
a+b
c+d
a+c b+d N
-
Fracture No Fracture
Swelling 32 40
No Swelling 8 120
Total 40 160
20/03/2015Role of Diagnostic test 14
Sensitivity?Specificity?Positive predictive value?Negative Predictive value?
Likelihood ratio of test positive?Likelihood ratio of test negative?
-
20/03/2015Role of Diagnostic test 15
PrevalenvceSensitiivitySpecificity
PredictiveValue
Post-test Probability
Likelihood ratio
Pre-test Probability
-
20/03/2015 16Role of Diagnostic test
-
20/03/2015 17Role of Diagnostic test
-
20/03/2015 18Role of Diagnostic test
-
20/03/2015Role of Diagnostic test 19
To determine cutoff point
To compare tests
For Interval/ratio scale
-
Blood glucose level2 hrs after eating
(mg/dL)
Sensitivity (%) Specificity (%)
70 98.6 8.8
80 97.1 25.5
90 94.3 47.6
100 88.6 69.8
110 85.7 84.1
120 71.4 92.5
130 64.3 96.9
140 57.1 99.4
20/03/2015Role of Diagnostic test 20
-
Blood glucose level2 hrs after eating
(mg/dL)Sensitivity (%) Specificity (%)
150 50.0 99.6
160 47.1 99.8
170 42.9 100.0
180 38.6 100.0
190 34.3 100.0
200 27.1 100.0
20/03/2015Role of Diagnostic test 21
-
20/03/2015Role of Diagnostic test 22
-
20/03/2015Role of Diagnostic test 23
-
20/03/2015Role of Diagnostic test 24
-
20/03/2015Role of Diagnostic test 25
To rule in diagnosis
To rule out diagnosis
To screen people
-
20/03/2015Role of Diagnostic test 26
Sensitivity Specificity
Fletcher et al., 1996
-
20/03/2015Role of Diagnostic test 27
Sensitivity
Specificity
Fletcher et al., 1996
-
20/03/2015Role of Diagnostic test 28
-
In nominal scale, measured by un-weighted Kappa index
In ordinal scale, measured by weighted Kappa index
In interval/ratio scale, measured by coefficient of variation (CV)
Due to presence of either intra or inter observer variation.
In clinical setting known as clinical disagreement
It reflect of reproducibility
20/03/2015Role of Diagnostic test 29
-
20/03/2015Role of Diagnostic test 30
CV=SD
MeanX 100%
-
Gallop heard by1st observer
No Gallop heardby 1st observer
Total
Gallop heard by2nd observer
10 5 15
No Gallop heardby 2nd
observer
10 75 85
Total 20 80 100
20/03/2015Role of Diagnostic test 31
PO = (10 + 75) : 100 X 100% = 85%
-
Gallop heard by1st observer
No Gallop heard1st observer
Total
Gallop heard by2nd observer
10 (3) 5 15
No Gallop heardby 2nd
observer
10 75(68) 85
Total 20 80 100
20/03/2015Role of Diagnostic test 32
PC = (3 + 68) : 100 X 100% = 71%
-
20/03/2015Role of Diagnostic test 33
K =100% - PC
PO - PC
100% - 71%
85% - 71%K =
K = 0.48
-
K = Po-Pc: 1-Pc
Po = Proportion of observed agreement
Pc = Proportion of Chance-expected
agreement
-1 < K < + 1
Po = 1, K = 1, complete agreement
Po > Pc, K > 0, Better than chance agreement
Po = Pc, K = 0, Equel to chance agrement
Po < Pc, K < 0, Poorer than chance agreement
20/03/2015Role of Diagnostic test 34
-
20/03/2015Role of Diagnostic test 35
Examiner
The Examined
Examination
-
20/03/2015Role of Diagnostic test 36
Biologic variation in the sense
The tendency to record inference rather than evidence
Ensnarement by diagnostic classification schemes
Entrapment by prior expectation
Simple incompetency
-
20/03/2015Role of Diagnostic test 37
Biologic variation in the system being examined
Effects of illness and medication
Memory and rumination chance agreement
Toss-ups
-
20/03/2015Role of Diagnostic test 38
Disruptive environments for the
examination
Disruptive interacting between examiners
and examined
Incorrect function or use of diagnostic tools
-
29%
71%
Role of Diagnostic test 3920/03/2015
Inappropriate prescription
Galula et al., 2006, Gastroenterol Clin Biol; 30: 517-524
-
49%
45%
5% 1%
Imprecise
Exessive
Erroneous
Insufficient
Role of Diagnostic test 4020/03/2015
Galula et al., 2006, Gastroenterol Clin Biol; 30: 517-524
-
20/03/2015Role of Diagnostic test 41
Fletcher RH., Fletcher SW danWagner EH., 1996, Clinical Epidemiology The Essentials, 3rd
ed., William & Wilkins, Baltimore
-
20/03/2015Role of Diagnostic test 42