Depending on which machine you are running the BNP on, it may take 2 hrs or 24hrs for the Natrecor to "wash. The patient should not be tested for BNP immediately after taking Natrecor. You are getting elevated levels and are inaccurate. BNP has to run through the renal system and depending on the pt's age, that system may not be that good. If the pt's is 75 the cutoff is 450pg/mL. The problem is if you have a 75 tr old pt's that is at 250 and "at risk" and the next day they turn 76. Now they are fine.