Variability of NT-proBNP plasma and urine levels in patients with stable heart failure:: a 2-year follow-up study

Objectives: To examine N-terminal pro-brain natriuretic peptide (NT-proBNP) variability in plasma and urine samples of patients with stable heart failure (HF) during a 24-month follow-up. Design: Prospective study. Setting: Teaching hospital based study. Patients: 74 clinically and functionally stable patients (NYHA class 2 +/- 0.5) out of 114 patients diagnosed with HF were followed up, and NT- proBNP plasma and urine levels were measured at baseline, 12 and 24 months. Results: Significant differences in mean urinary levels (p < 0.01) were found during follow- up, but no changes were found in plasma. Bland-Altman plots showed few variations in plasma percentages in the three intervals ( stage I-basal; stage II-stage I; stage II-basal) with a coefficient of reproducibility (CR) of 22%, 21% and 25%, respectively. Changes in NT- proBNP urinary levels had a CR of 7.1%, 6.8% and 9.4% at the three intervals, respectively. A good correlation was found between plasma and urinary levels of NT- proBNP (p < 0.001) and between the different NT-proBNP plasma (p < 0.001) and urine measurements (p < 0.001). Conclusions: NT-proBNP plasma and urine levels show good stability in a 24-month follow-up of patients with stable heart failure. Thus, assessment of urinary and plasma NT-proBNP concentrations may be a useful tool for monitoring patients with HF during follow-up. The results suggest that variations in peptide concentrations exceeding 22% in plasma and 7% in urine in a 12-month follow-up and 25% and 9% in a 24-month follow-up may indicate pathophysiological changes.