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Figure 4 Receiver-operating characteristic curves for the five assays for the diagnosis of heart failure. A range of cut-off values for the commercially available Biosite brain natriuretic peptide (BNP) and Roche N-terminal brain natriuretic peptide (N-BNP) assays are given at the bottom of the figure; the highlighted row represents the optimal value for specificity and sensitivity. ACC = overall accuracy of the test; AUC = area under the receiver-operating characteristic curve; NPV = negative predictive value; PPV = positive predictive value; Spec = specificity; Sens = sensitivity. The arrows indicate the optimum value for cut-off for specificity and sensitivity, defined as the point geometrically closest to perfect sensitivity and specificity. Overall accuracy of the test is defined as the percentage of patients correctly classified as having heart failure or not. Clinical BNP = local clinical BNP assay; Biosite BNP = Biosite point-of-care BNP assay; Research BNP = local research BNP assay; Roche N-BNP = Roche N-BNP assay; Local N-BNP = local N-BNP assay.
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