Substantial intraindividual variability of BNP concentrations in patients with hypertension
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Plasma concentrations of B-type natriuretic peptides (BNP) independently predict the risk of death and cardiovascular events. In the present study, we investigated the intraindividual variability of BNP concentrations, a potential confounder of risk prediction. Consecutive outpatients with blood pressure (BP) values of at least 140/90 mm Hg and not taking BP lowering therapy were asked to participate. Exclusion criteria were renal insufficiency, structural heart disease on echocardiography, except left ventricular hypertrophy and any other severe concomitant illness. Plasma BNP levels were determined on two different days using the same assay. In total, 77 patients were included. Mean age was 54+/-12 years, 55% were male and mean systolic/diastolic BP was 163+/-16/96+/-8 mm Hg. Mean creatinine was 70+/-14 micromol/l. The median interval between the two BNP assays was 10 days (interquartile range 1-23 days). Median BNP concentrations were 17 and 16 pg/ml for the first and second visit, respectively (P=0.48). However, there was a wide range of differences in BNP values among individual patients, 34 patients (44%) having an absolute difference of at least 10 pg/ml. When patients were categorized according to tertiles of BNP levels, 25 (32%) changed from one tertile at the first visit to another at the second visit. In conclusion, these data indicate that BNP levels may be used on a population level. However, the high intraindividual variability seems to preclude useful risk stratification in the individual patient. Care should be taken in the interpretation of single BNP values below the currently accepted thresholds for heart failure.
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