The reliability of medication inventory methods compared to serum levels of cardiovascular drugs in the elderly

Medication inventory is more reliable than self-report in assessing prescri ption drug use in elderly populations. it is not known how strongly medicat ion inventory reflects actual medication use as measured by serum drug leve ls. In the Cardiovascular Health Study, medication data were collected annu ally by study interviewers from medication containers brought to the clinic visit. At the fourth clinic visit, venipuncture was performed under 12-hou r fasting conditions. Participants were told to take medications as usual. Eased on medication inventory results, we randomly selected 55 users and 55 non-users oi four cardiovascular drugs: aspirin, propranolol, hydrochlorot hiazide, and digoxin. All 110 blood samples for each of the four drugs were analyzed; cut points were based on detectable levels given laboratory limi tations. Kappa statistics (K) tested degree of agreement between medication inventory findings and serum detection. Assays were completed on 400 sampl es (91%). Agreement for aspirin (n = 102) was poor: K = 0.16 (95% CI: 0.0-0 .32). Agreement for propranolol (n = 98) was fair: K = 0.43 (95% CI: 0.27-0 .59). Agreement for hydrochlorothiazide (n = 100) was good: K = 0.62 (95% C I: 0.53-0.91). Agreement for digoxin (n = 100) was excellent: K = 0.94 (95% CI: 0.74-1.0). For four all drugs, lack of agreement was confined primaril y to participants who reported use but did not have detectable levels. Excl uding aspirin users, only one non-user (0.7%) had drug detected in serum. T he medication inventory is a reasonably sensitive and a fairly reliable met hod for ascertaining non-aspirin cardiovascular drug use in the elderly eve n though this method may overestimate use as assessed by serum level. J CLI N EPIDEMIOL 52;2:143-146, 1999. (C) 1999 Elsevier Science Inc.