[Non-radioimmunometric NT-ProBNP and BNP assays: impact of diluent, age, gender, BMI]

We examined the analytical correlation between non-radioimmunometric plasma N-terminal pro-brain natriuretic peptide (NT-proBNP) and B-type natriuretic peptide (BNP) and evaluated whether NT-proBNP or BNP was influenced by age, gender and/or body mass index (BMI). Electro-chemiluminescence (Elecsys, Roche diagnostic) and a single use fluorescence (Triage, Biosite) immunoassays were used to measure NT-proBNP and BNP levels respectively. As a preliminary, seven different diluents usually used in immunoassays were tested and the "speciality diluent" (Ortho Clinical Diagnostic) was validated to increase the linearity of BNP immunoassay above 5000 pg/mL. Data were collected prospectively from patients admitted to the emergency department for acute dyspnea. Plasma BNP and NT-proBNP were measured at admission. Reference diagnosis was adjudicated by 2 independent cardiologists using the European Society of Cardiology guidelines. One hundred and sixty consecutive patients were included: 84 females and 76 males, mean age 80.1 +/- 13.5 (16-98). The analytical correlation between NT-proBNP and BNP was satisfactory using the equation: log10(NT-proBNP) = 1.1xlog10(BNP) + 0.57 and a correlation r = 0.93. This was established over a wide range of concentration (5-6400 pg/mL for BNP). Age and gender were known to influence circulating BNP levels. We showed that the correlation between BNP and NT-proBNP was not influenced by age, gender and body mass index of patients which suggests that the distribution of both peptides was similarly affected by these parameters. We conclude that NT-proBNP, as assayed in the present study, correlates closely with BNP. Used in conjunction with other clinical information, rapid measurement of BNP or NT-proBNP is useful in establishing or excluding the diagnosis of congestive heart failure in patients with acute dyspnea.