Could BNP screening of acute chest pain cases lead to safe earlier discharge of patients with non-cardiac causes? A pilot study

Background: The assessment of chest pain relies on clinical assessment and markers of cell necrosis such as Troponin T (TnT). B-type natriuretic peptide (BNP) is also raised in myocardial ischaemia and therefore may be useful in deciding if acute chest pain is of cardiac origin or not. Aim: To investigate the role of BNP in the assessment of unselected patients presenting with acute chest pain. Methods: A prospective observational study of 100 patients presenting with chest pain to the Acute Medical Admissions Unit was carried out. All patients had BNP and TnT levels measured. The primary outcome was categorization of chest pain as cardiac or non-cardiac. This was determined by the discharge diagnosis. BNP cutoffs were derived from a receiver operated characteristic (ROC) curve. The sensitivity, specificity, positive predictive accuracy (PPA) and negative predictive accuracy (NPA) were all calculated for BNP, TnT and for the composite of BNP and TnT. Results: Mean BNP in patients with cardiac chest pain was significantly greater than mean BNP for patients with non-cardiac chest pain (P <= 0.0001). BNP was significantly more sensitive than TnT (P = 0.003). However TnT was more specific than BNP (98% vs. 75%, P <= 0.0001). Combining BNP and TnT increased sensitivity from 55.6% to 95.6.% Conclusion: Our findings suggest that BNP is more sensitive but less specific than TnT in the diagnostic assessment of acute chest pain. However, combining BNP and TnT was a very satisfactory rule out test (negative predictive accuracy 96%) for excluding chest pain that had a cardiac origin.