Introduction of an NT-proBNP assay to an acute admission unit--a 2-year audit

The differential diagnosis of dyspnoea is difficult due to the low predictive value of clinical and laboratory parameters. The elevated levels of NT-proBNP in congestive heart failure may improve diagnostic accuracy. We have evaluated the effect of the introduction of an NT-proBNP assay on hospital length of stay (LOS) and mortality.

There were 11,853 AMAU patient episodes in the 22 months study period (March 2005-Dec 2006). An NT-proBNP assay was requested in 657 (5.5%) of these. Comparison between categorical variables such as diagnosis, NT-proBNP testing, LOS, and in-hospital mortality was made using Chi-square tests. Literature review suggested that an NT-proBNP cut-off >or=5000 ng/L should predict acute in-patient mortality. Logistic regression analysis was used to examine the association between such an elevated NT-proBNP level and outcomes.

Of the 396 patients with NT-proBNP <5000 ng/L, 8.1% died compared with 22.5% of the 178 patients dying with values >or=5000 ng/L (p<0.0001). An NT-proBNP >or=5000 ng/L was predictive of both LOS >or=9 days (odds ratios (OR) 1.54 (95% CI 1.06, 2.24: p=0.02) and LOS >or=14 days (OR=1.87 (95% CI 1.29, 2.71: p=0.0009). NT-proBNP requests increased over time, from 2.6% to 8.2% of all patients; the result fell in the diagnostic range for CHF in 60% of requests.

The introduction of an NT-proBNP was reflected in an appropriate but rapidly increasing pattern of requests from clinicians. High NT-proBNP levels predicted in-hospital mortality and longer LOS in an acute medical population.