Response to the captopril test is dependent on baseline renin profile.

OBJECTIVE

To determine prospectively the relationship between the renin-sodium profile and the renin response to captopril challenge in patients with essential hypertension.

DESIGN

A standard captopril test was performed in 108 uncomplicated, untreated hypertensive subjects with normal renal function and urinary sodium excretion in the range 50-240 mmol/day. The subjects were selected from a working population with a low expected prevalence of renovascular disease.

METHOD

The captopril test was considered positive if the captopril-induced rise in plasma renin activity met all three criteria established by Müller et al. Patients with a positive test and those meeting only one or two of the three criteria were further investigated for renovascular hypertension by measuring renal venous renins and by digital subtraction intravenous angiography. Renin responses were analyzed according to baseline renin-sodium profile.

RESULTS

Nine of 108 subjects had a false-positive captopril test result. Among the subjects with a low or normal renin-sodium profile, 1% (one of 82) had a false-positive result. In contrast, false-positive results were seen in 31% (eight of 26) of high-renin subjects. False-positive test results were not related to urinary sodium excretion or to excessive decrease in blood pressure. The magnitude of the renin response to captopril was strongly and directly related to the baseline plasma renin activity.

CONCLUSION

An exaggerated renin response to captopril challenge is common in patients with high-renin essential hypertension. Therefore, in a population with a low probability of renovascular hypertension, caution is recommended in interpreting a positive test result in patients with a high baseline renin.