Ordering of the serum angiotensin-converting enzyme test in patients receiving angiotensin-converting enzyme inhibitor th erapy an avoidable but common error

BACKGROUND: Serum angiotensin-converting enzyme (ACE) levels may be decreased by use of ACE inhibitor (ACEI) medication. In this study, we determined how oft en ACE levels were measured in patients receiving ACEI therapy. METHODS: ACE levels analyzed over a 54-month preintervention time period at an academic medical center were reviewed retrospectively for tests performed during ACEI therapy. Th ese data were compared with a large, deidentifi ed dataset of ACE levels measured at a national reference laboratory; in vitro studies of ACEI inhibition; and liquid chromatography time-of-fl ight mass spectrometry detection of lisinopril in a subset of clinical specimens. RESULTS: Over a 54-month period, 1,292 patients had ACE levels measured, with 108 patients (8.4%) receiving ACEI therapy at the time of testing. ACE levels measured for patients receiving ACEI therapy were substantially lower. In general, clinical teams did not recognize a medication eff ect on ACE levels. Introduction of a warning prompt in the electronic health record reduced the ordering of ACE levels in patients receiving ACEIs by. 60% in a 17-month postintervention time period. Th e deidentifi ed dataset of ACE levels at a reference laboratory showed a bimodal distribution, with a peak of very low ACE levels. Using liquid chromatography time-of-fl ight mass spectrometry, the presence of lisinopril was confi rmed in a subset of specimens with low ACE activity. In vitro studies of two diff erent ACE assays showed signifi cant inhibition of activity at clinically relevant concentrations. CONCLUSIONS: Assessment of ACE activity is oft en measured for patients receiving ACEIs, potentially leading to low ACE concentrations and inaccurate interpretations.