3 Receiver Operating Characteristic Curve (ROC) The name "Receiver Operating Characteristic" came from "Signal Detection Theory" developed during World War II for the analysis of radar images.Radar operators had to decide whether a blip on the screen represented an enemy target, a friendly ship, or just noise.Signal detection theory measures the ability of radar receiver operators to make these important distinctions. Their ability to do so was called the Receiver Operating Characteristics.
4 ROC curves were developed in the 1950's as a by-product of research into making sense of radio signals contaminated by noise.During 1970's that signal detection theory was recognized as useful for interpreting medical test results.More recently it's become clear that they are remarkably useful in medical decision-making
5 ROC curves plot the sensitivity of a test versus its false positive rate for various points ROC analysis has wide applicability in radiology research for comparing observers, modalities, and tests.
6 T4 valueHypothyroidEuthyroid5 or less1817174369 or more339Totals:3293T4 valueHypothyroidEuthyroid5 or less181> 51492Totals:3293T4 valueHypothyroidEuthyroid7 or less2518> 7775Totals:3293
8 No test distinguish normal from disease with 100% accuracy. The sensitivity and specificity of a diagnostic test depends on more than just the "quality" of the test.They also depend on the definition of what constitutes an abnormal test.No test distinguish normal from disease with 100% accuracy.The area of overlap indicates where the test cannot distinguish normal from disease.The sensitivity and specificity of a diagnostic test depends on more than just the "quality" of the testThey also depend on the definition of what constitutes an abnormal test.No test distinguish normal from disease with 100% accuracy.The area of overlap indicates where the test cannot distinguish normal from disease.
10 This graph shows three ROC curves representing excellent, good, and worthless tests plotted on the same graph.The accuracy of the test depends on how well the test separates the group being tested into those with and without the disease in question.Accuracy is measured by the area under the ROC curve. An area of 1 represents a perfect test; an area of .5 represents a worthless test.A rough guide for classifying the accuracy of a diagnostic test is the traditional academic point system:0.90 – 1.00 = excellent= good= fair= poorIt is a plot of the true positive rate against the false positive rate for the different possible cut points of a diagnostic testIt shows the tradeoff between sensitivity and specificity (any increase in sensitivity will be accompanied by a decrease in specificity).The closer the curve follows the left-hand border and then the top border of the ROC space, the more accurate the test.The closer the curve comes to the 45-degree diagonal of the ROC space, the less accurate the test.Accurecy is how good is the test ro discremenate between diseasesd and non-diseased.
11 IntroductionCardiac troponin testing is central to the diagnosis of acute myocardial infarctionAn early diagnosis of AMI facilitates rapid decision making and treatment and therefore improves the outcome in patients presenting with chest pain.Introduction of cardiac markers is a milestone in cardiology.The sensitivity of the available cardiac markers is weak within the first hours after the onset of chest pain
12 Is Sensitive trop sensitive enough? ????????Is Sensitive trop sensitive enough?In early diagnosis of MI
13 Methods Study Population. They enrolled 1818 consecutive patients presenting with new-onset chest pain at chest-pain units at three German study centers between January 2007 and December 2008Study was approved by local ethics committeesAll patients provided written informed consent
14 Inclusion:Age between 18 to 85 yearsAngina pectoris or equivalentExclusion criteriaMajor surgery or trauma within the previous 4 weeksPregnancyIV drug abuseHemoglobin level <10 g/dL.
15 Blood was drawn for routine blood work and sample storage at admission, 3 and 6 hours after Concordantly, a 12-lead ECG was obtained.All patients were followed up 30 days after initial hospitalizationAdditionally , the local civil registry office provided information about death.Follow-up information was available in 98% of the population.
16 Outcome measures:composite of death.MI.Stroke.Hospital admission because of cardio-vascular reasons .Need for unplanned coronary intervention
17 Chest pain onset time was carefully assessed by independent research staff. Troponin I Ultra was purchased from Siemens Healthcare Diagnostics, which had no role in the design of the study or analysis of the results.
18 In-house troponin TropT (Roche Diagnostics, Germany) or Trop I (Siemens Healthcare Diagnostics).Detection limits are 0.01 ng/mL (Troponin T) and 0.04 ng/mL (Troponin I) with assay ranges of ng/mL (Troponin T) and ng/mL (Troponin I), respectively.Reference limits based on the 99th percentile for a healthy population are 0.01 ng/mL (Troponin T) and 0.07 ng/mL (Troponin I) with 10% CV cut-offs of 0.03 ng/mL (Troponin T) and 0.14 ng/mL (Troponin I), respectively.
19 Laboratory Methods Investigational troponin Investigational troponin I was measured with the TnI-Ultra assay on an ADVIA Centaur XP system (Siemens Healthcare Diagnostics, Germany).The assay range is ng/mL.The reference limit based on the 99th percentile for a healthy population is 0.04 ng/mL
20 Adjudication of the Final Diagnosis Based on all available clinical, laboratory, and imaging findingsAdjudicated by an expert committee of two independent cardiologists who were unaware of the results of the troponin I assays
21 Diagnosis Based on Conventional Troponin Assays Primary diagnosis of AMI was adjudicated according to current guidelines .Evidence of myocardial necrosis that was consistent withmyocardial ischemia, together with clinical symptomsof ischemiaorECG changes indicative of new ischemia (new ST-segment or T-wavechanges or new LBBB)Imaging evidence of new loss of viable myocardiumDetection of a culprit lesion on coronary angiographyMyocardial necrosis was documented if there was at least one value above the cutoff value for 10% imprecision of the respective conventional troponin test together with a rising or falling pattern of at least 20% within 6 hours after admission to distinguish background elevated troponin levels from acute elevation.The conventional Troponin I assay was used only for the diagnosis of myocardial infarction and not for comparisons with the sensitive troponin I assay.In 95.2% of the patients who were classified as having acute myocardial infarction on the basis of the definition outlined above, coronary angiography identified a culprit lesion that accounted for the increase in the patient's troponin level.
22 Diagnosis Based on Sensitive Troponin I Assay They used the concentration of 0.04 ng per mL as the upper reference limit and established the diagnosis of myocardial infarction if one value of more than 0.04 ng per mL was documented,combined with a rise or fall in the value of 30% or more within 6 hours after admission.
23 Statistical AnalysisSkewed variables were described by median and interquartile range.Normally distributed variables were characterized by their arithmetic mean and standard deviation.They calculated ROC curves on the basis of the continuously measured biomarker levels by taking every measured biomarker level as a cutoff value and then deriving sensitivity and specificity values from the resulting two-by-two tables for each cutoff value.The diagnosis variable used for the two by two tables contrasted non-coronary chest pain against acute myocardial infarction.
24 P values are based on the Wald z-test statistic All statistical analyses were performed with the use of R software (version 2.8.1) and SAS software (version 9.2).
28 sensitivity for the sensitive troponin I assay was 90 sensitivity for the sensitive troponin I assay was 90.7%, and the specificity was 90.2%, regardless of the interval between the onset of chest pain and admission .A total of 240 of the 1818 patients (13.2%) presented with unstable angina . Of these patients, 53 (22.1%) had troponin I levels of more than 0.04 ng per milliliter as measured with the sensitive assay. With the use of this assay to differentiate unstable angina from noncoronary chest pain, the
29 Figure 2 shows the association between an elevated value on admission and the diagnosis of acute myocardial infarction, according to the time of chest-pain onset. In patients presenting within 3 hours after the onset of chest pain, 184 of 227 patients with diagnosed myocardial infarction (81.1%) had a single troponin I level of more than 0.04 ng per milliliter on admission, for a negative predictive value of 84.1% and a positive predictive value of 86.7%. Overall, the AUC of the baseline troponin I level was approximately 0.90, regardless of the time of chest-pain onset.
30 Second, we calculated the time it took to diagnose myocardial infarction in 95 to 100% of patients using the sensitive troponin I assay (Table 3). A total of 88% of myocardial infarctions were detected on admission in patients presenting within 6 hours after the onset of chest pain, and 95% of myocardial infarctions were detected in those presenting between 6 and 12 hours after the onset of chest pain. With serial measurements (on admission and 3 or 6 hours after admission), the rate of detection of myocardial infarction was 100%.
31 Low or Moderate Troponin I Levels 585 pts86 pts6HModer. Elevated.(>0.04 ) without rise or fall (<30%)in repeated testing.115 pt > 0.04Of 585 patients in whom troponin I levels, as measured with the sensitive assay, were between the limit of detection (0.006 ng per milliliter) and the 99th percentile (0.04 ng per milliliter) on admission, 115 patients (19.7%) had levels of more than 0.04 ng per milliliter within 6 hours after hospital admission. Of these patients, only 30 were categorized as having acute myocardial infarction on the basis of conventional troponin measurement; in 29 of the 30 patients, myocardial infarction was confirmed angiographically. A total of 87 patients had moderately elevated troponin I levels (>0.04 ng per milliliter) without a rise or fall of 30% in subsequent samples. Of these patients, 62 had a distinct noncoronary diagnosis (Table 1 in the Supplementary Appendix); none of the 62 patients had an adverse event during the 30-day follow-up.30 pts diagnosed as AMI according to trop T62 had a distinct non-coronary diagnosis
32 Short-Term OutcomeA troponin I level of more than 0.04 ng per milliliter was independently associated with an increased risk of an adverse outcome at 30 days (hazard ratio, 1.96; 95% confidence interval, 1.27 to 3.05; P=0.003).
34 Assessment of validity Was there an independent, blind comparison with a reference standard (gold standard) of diagnosis?Was the diagnostic test evaluated in an appropriate spectrum of patients?Were all patients analyzed in the groups to which they were randomized (intention to treat analysis)?Was the test, or group of tests, validated in a second, independent group of patients?
35 Assessment of importance of the results Are likelihood ratios or data necessary for their calculation provided for the diagnostic test?Target DisorderTotalsPresentAbsentDiagnostic Test ResultPositiveaba+bNegativecdc+da+cb+da+b+c+d
36 Sensitivity = a/(a+c)Specificity = d/(b+d)Likelihood ratio for a positive test result = LR+ = sens/(1-spec)Likelihood ratio for a negative test result = LR - = (1-sens)/specPositive Predictive Value = a/(a+b)Negative Predictive Value = d/(c+d)Pre-test probability (prevalence) = (a+c)/(a+b+c+d)Post-test odds=prevalence/(1-prevlance) x LRPost-test probability = post-test odds/(post-test odds +1)
37 Assessment of Utility: Will the reproducibility of the test result and its interpretation be satisfactory in my setting?Are the results applicable to my patient?Will the results change my management?Will patients be better off as a result of the test?