When ordering renin-to-aldosterone ratios in the workup of secondary hypertension, how does one deal with the severe hypertension that results when the patient discontinues both ACE inhibitors and diuretics before the blood draw?
—Raymond S. Chen, DO, Monterey Park, Calif.

If I am considering the diagnosis of hyperaldosteronism, which is associated with low renin and high aldosterone levels, I attempt to control BP with a combination, e.g., a calcium channel blocker and an alpha blocker. Such a combination is highly effective in volume-mediated, low-renin hypertension and has little effect on renin and aldosterone values. If necessary, I continue the ACE inhibitor, which has little effect on renin in patients with a low renin. A diuretic, which would increase renin, is best avoided, if possible, during testing. If the diuretic cannot be stopped, however, a low renin determination combined with a high aldosterone would still be informative. A higher renin would not rule out primary hyperaldosteronism. Note that an aldosterone antagonist, such as spironolactone, must be stopped for up to six weeks. Finally, a beta blocker will typically result in a low renin and reduce the specificity of the renin-to-aldosterone ratio.

In the workup for renovascular hypertension, it is a high renin that increases suspicion of the diagnosis. Both an ACE inhibitor and a diuretic increase renin, and a low renin in a patient on either agent argues against the diagnosis. A high renin would have low specificity for the diagnosis. Finally, beta blockers do suppress renin in patients with renovascular hypertension, and therefore, a low renin while on a beta blocker does not rule out renovascular hypertension. A high renin would increase suspicion of the diagnosis.
—Samuel J. Mann, MD (110-10)

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