Is this evidence about the accuracy of a diagnostic test valid?Does this evidence demonstrate an important ability of this test to accurately distinguish patients who do and dont have a specific disease?Can I apply this valid diagnostic test to a specific patient?

Blinding comparison with a gold standard of diagnosisAppropriate spectrum of patientsApplication of the gold standard regardless of the diagnostic test resultsValidated in a second, independent group of patients

SensitivitySpecificityLikelihood ratioPre-test probabilityPost-test probabilityDoes this evidence demonstrate an important ability of this test accurately distinguish patients who do and dont have a specific disorder?

LR + = sens/(1-spec)LR - = (1-sens)/specPrevalence = (a+c)/(a+b+c+d)Pre-test odds = prevalence/(1 prevalence) =Post-test odds = pre-test odds x likelihood ratioPost-test probability = post-test odds/(post-test odds + 1)Sensitivity= a / (a+c)Specificity= d / (b+d)PPV = a/ (a+b)NPV = d / (c+d)

TESPENYAKITADA TDK+aba+b-cdc+dTotala + cb + d

Should be available, affordable, accurate, and precise in our settingValid pre-test probability of patientsThe resulting post-test probability affect the management of patient

ABPre-test probability of target disorder

Do not test

Do not treatTest, and treat on the basis of the tests resultsDo not test

Get on with treatment

Sensitivity, specificityLikelihood RatioTest selection according to Operating CharacteristicsOperating Characteristic of Combination TestingCutoff Point and ROC *

Very sensitive test, such test when normal, exclude the disease*Very specific test, such test when abnormal, confirm the presence of disease

If the disease is present, what is the likelihood that the test result will positive? (Sensitivity of the test)If the disease is not present, what is the likelihood that the test result will be normal? (Specificity of the test)If the patient has a positive test, what/s the likelihood that the patient really has the disease (PPV)If the patient has a negative test, whats the likelihood that the patient really does not have the disease (NPV)Likelihood ratio the probability of disease alter positive test or negative test.*

*DISEASETESTPresentAbsentPositiveNegativeabcda+ca+b PPV=a/a+bLR + = Se/1-SpLR - = 1-Se/SpP= a+c/a+b+c+dSp=d/b+dSe=a/a+ca+b+c+db+dc+d NPV=d/c+d

Importance of knowledge of the test charactersitics:to facilitate proper interpretation of results,to decide which test select for a given purpose*Tine-testAplitestMono-vacSensitivity88%91%99% *Specificity96%95%94% *