Clinical chemistry
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Most quantitative diagnostic tests do not perfectly differentiate between persons with and without a given disease. We present a simple method to construct a 3-zone partition for quantitative tests results, including positive and negative zones and a gray zone between, and we describe its use in the diagnosis of heart failure by brain natriuretic peptide (BNP) measurement in acute dyspneic patients. ⋯ The gray zone approach applied to the diagnosis of heart failure by BNP might allow sensible cutoff values to be determined for clinical practice according to relevant subgroups of patients. The gray zone approach might be usefully applied to many other quantitative tests and clinical diagnostic or screening problems.