We describe the value of Nt-proBNP in relation to cardiac normality and risk of major adverse cardiac events (MACE) in consecutive hospitalised patients below and above 75 years of age.
Method: During a 10 month period 2224 consecutive patients, admitted to all departments in a general city hospital, had a full cardiac examination and were prospectively followed for 1 year. We identified a normal group (without obvious heart disease) and a group with MACE (significant heart disease at admission or a cardiac event within the following 90 days). NT-proBNP measurements were done using an ELISA-a two-step sandwich assay with streptavidin coated microtitre plates.
Results: The age dependent 90th percentiles of Nt-proBNP in the normal group were approximately 3 times higher than values reported in previous community studies. Elderly patients had 3-fold higher absolute cut off values than did patients under the age of 75 years. One-hundred-and-sixteen patients had a MACE, and areas under the receiver operating curve (ROC) to predict a MACE were 0.83 (from 40 to 59 years), 0.82 (60 to 74) and 0.79 (from 75 years). In younger patients, the upper limit of Nt-proBNP in normal patients was similar to the value, which defined the top quintile of risk. In patients aged greater than 75 years the predictive cut point included more than 40% of the population.
Conclusion: Nt-proBNP was useful at all ages but specificity was slightly lower in the elderly. Cut off values in hospitalised cardiac normal patients are approximately three times higher than community derived values.