Using the single-compartment ratio model to calculate half-life, NT-proBNP as an example.

Background: The single-compartment model offers a simple way to calculate the half-life of a compound if it is secreted or injected at the known rate compared with another compound whose half-life is known. This model may be easier to use than the exponential decay model. Investigators disagree on the value of the half-life of NT-proBNP, with published values ranging from 70 to 120 min. Prior studies used values from sheep, which may not be appropriate in humans. Therefore, we have re-evaluated the half-life of NT-proBNP using a single-compartment model.

Methods: The single-compartment model allows one to evaluate the half-life of NT-proBNP using the NT-proBNP:BNP ratio and the BNP half-life. We calculated the NT-proBNP:BNP ratio from 26 subjects without cardiac abnormalities.

Results: The mean ratio of the NT-proBNP to BNP was 1.24 with an SEM of 0.1. Using a half-life of 20 min for BNP, the calculated half-life for NT-proBNP would be 24.8 min.

Conclusions: The single-compartment ratio model requires neither strictly first-order decay after stimulation, nor the collection of times samples. The re-calculated half-life for NT-proBNP is 25 min for humans, which differs greatly from the current literature value of 90 min and thus its half-life is closer to that of BNP in normal subjects. Accordingly its estimated time to return to a steady-state after a disturbance is 100 min, and therefore it could be useful in the monitoring of patients over short time periods. The single-compartment ratio model is fairly robust in the presence of cross-reactivity.