For an individual congestive heart failure (CHF) patient to gain maximum benefit from their angiotensin converting enzyme (ACE) inhibitor treatment, it is important for him or her to adhere fully with treatment. Many studies suggest that non-adherence with drug treatment is common in CHF patients and that this leads to increased hospitalisation and even death.1 Since ACE inhibitors reduce mortality, it is self evident that non-adherence will increase mortality. As CHF patients tend to be elderly and on multiple treatments, it is unsurprising that non-adherence should be a common problem in this patient group.2 However, assessing treatment adherence is notoriously difficult and all assessments of adherence are less than perfect.

In the case of adherence with an ACE inhibitor, a unique opportunity presents itself—that is, to use serum ACE measurements to assess adherence. This measurement is very robust by a variety of technologies and intrasubject variability or assay related variability is minimal (> 2%), even in the unsuppressed state.3 We have previously established that this is …