Laboratory testing in newly treated elderly hypertensive patients without co-morbidities: a population-based cohort study

BACKGROUND: Although a purported advantage of newer antihypertensive drug classes is a reduced need for laboratory testing, little is known about the frequency of laboratory monitoring of hypertensive patients in clinical practice and whether this differs across drug classes. METHODS: This population-based cohort study used linked administrative databases in Ontario, Canada. All elderly residents of Ontario (age 66 and over) who were newly treated for uncomplicated hypertension between 1994 and 2002 were followed for 24 months or until they were admitted to hospital, died, or were no longer on their initially prescribed monotherapy. We examined the frequency and type of laboratory tests performed while patients were treated with antihypertensive monotherapy. RESULTS: In a cohort of 164,413 patients, 39% were treated with thiazides and 46% were prescribed "newer" drug classes as initial therapy. At baseline, 96,534 patients (59%) did not have any laboratory testing done, and during 1,701,520 months of monotherapy (mean time on initial agent 10.3 months) only 79,985 (49%) had any tests done. Laboratory testing was significantly less frequent in patients prescribed newer drug classes than thiazides: the adjusted rate ratios for laboratory testing were 0.94 (95% confidence interval [CI] 0.93–0.95) with angiotensin-converting enzyme inhibitors, 0.80 (95% CI 0.79–0.81) with calcium-channel blockers, and 0.79 (95% CI 0.76–0.82) with angiotensin-receptor blockers. However, the absolute increase in testing was small (16 extra electrolyte tests, 6 extra renal function tests, 4 extra glucose tests, and 6 fewer serum cholesterol tests per 100 patients every 6 months), such that the extra laboratory testing observed with thiazides resulted in an additional cost of only C$0.63 per patient every 6 months in comparison with the cost of the newer drug classes. CONCLUSION: Laboratory testing in clinical practice was significantly less frequent among patients prescribed newer drug classes than among those prescribed thiazides; however, laboratory monitoring was infrequent in this cohort of elderly patients with hypertension but without comorbidities, and the magnitude of differences between drug classes was small.