It is important to consider secondary causes of hypertension (eg, renovascular hypertension) that may have precipitated the crisis. A single dose captopril (Capoten) challenge test may be performed, particularly in patients who have not received previous medical therapy for hypertension. Baseline plasma renin activity is measured and the patient is given 25 to 50 mg of captopril; measurement is repeated 60 minutes later. Test sensitivity is excellent but specificity is poor. Thus, further testing (eg, renal arterial Doppler ultrasonography, renal magnetic resonance angiography, contrast angiography) may be necessary to confirm diagnosis. Before initiating therapy, metanephrine levels can be measured by performing spot urine test to rule out the presence of pheochromocytoma. Plasma aldosterone and renin levels should be tested to rule out primary hyperaldosteronism in patients with significant hypokalemia who are not taking diuretics at the time of presentation.
· Patient maintains normal salt intake and receives no diuretics.
· Withdraw all antihypertensives 3 weeks before the test, if possible
· Patient should be seated for at least 30 minutes; draw venous blood sample and measure baseline
plasma renin activity
· Dilute 50 mg of captopril (Capoten) in 10 mL of water; patient immediately drinks the solution
· After 60 minutes, draw venous blood samples and measure stimulated plasma renin activity
Test is positive in the presence of:
· Stimulated plasma renin activity of 12 ng/mL/hr or more and
· Absolute increase in plasma renin activity of 10 ng.mL.hr or more and
· 150% increase in stimulate plasma renin activity or
400% increase if baseline plasma renin activity is <3 ng/mL/hr