Role of Diagnostic Test-Osman Sianipar-CE and BU-Clinical Pathology (2015)

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


To rule in

To rule out

To screen

Diagnosis

To monitore the treatment


precise but

not accurate

Accurate but

not preciseAccurate and precise


Accurate Not accurate

Precise

Not precise



Interval

Ratio

Ordinal

Nominal

Accuracy Precision

Sensitivity

Specificity

Positive predictive value

Negative predictive value

Likelihood ratio

Unweightedkappa index



+ -

+

Disease

T

e

s

t

True

positive

False

positive

False

negative

True

negative-


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


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


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


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


Sensitivity?Specificity?Positive predictive value?Negative Predictive value?

Likelihood ratio of test positive?Likelihood ratio of test negative?


PrevalenvceSensitiivitySpecificity

PredictiveValue

Post-test Probability

Likelihood ratio

Pre-test Probability


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


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



To rule in diagnosis

To rule out diagnosis

To screen people


Sensitivity Specificity

Fletcher et al., 1996


Sensitivity

Specificity

Fletcher et al., 1996

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



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


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


PC = (3 + 68) : 100 X 100% = 71%


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



Examiner

The Examined

Examination


Biologic variation in the sense

The tendency to record inference rather than evidence

Ensnarement by diagnostic classification schemes

Entrapment by prior expectation

Simple incompetency


Biologic variation in the system being examined

Effects of illness and medication

Memory and rumination chance agreement

Toss-ups


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


Fletcher RH., Fletcher SW danWagner EH., 1996, Clinical Epidemiology The Essentials, 3rd

ed., William & Wilkins, Baltimore

Role of Diagnostic Test-Osman Sianipar-CE and BU-Clinical Pathology (2015)

Documents

role of diagnostic testprecise

ratio of positive test

ratio of negative test

role of diagnostic testto

likelihood ratio positive

diseased group positive

diseased group specificity

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