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Figure 3 Receiver operating curves defining the sensitivity and specificity of brain natriuretic peptide (BNP) (by Shionogi and Biosite assays) for the detection of systolic dysfunction (ejection fraction 40%) in each age strata of men and women. The open circle indicates the BNP value at the upper reference limit as derived from the regression fit in each age/gender/assay stratum. The open triangle indicates the BNP value with optimal sensitivity and specificity (the "optimal point") on the receiver operating characteristic (ROC) curve.