Correct Answer
Your Answer: Salt (NaCl) loading suppression testing
This test relies on the principle that primary hyperaldosteronism is a volume-expanded state involving salt retention. Giving supplemental NaCl to such a patient should, therefore, not suppress plasma aldosterone.
Oral NaCl loading is accomplished by giving 50 mmol NaCl daily in divided doses, with a 24-hour urine collection for aldosterone excretion on day three. Primary hyperaldosteronism is diagnosed if aldosterone urinary excretion is not suppressed to less than 12 µg per 24-hr period during high sodium excretion (greater than 200 mEq/24-hr), but plasma renin activity is suppressed (less than 1.0 ng/ml/hr).
Other centers use fludrocortisone suppression testing as their diagnostic test of choice. The disadvantage is that the patient needs to be hospitalized for four days.
To differentiate further between a unilateral adenoma and bilateral adrenal hyperplasia as a source of autonomous aldosterone production, adrenal venous sampling is performed.
References:
Calhoun DA, Zaman MA, Nishizaka MK, et al. Hyperaldosteronism among black and white subjects with resistant hypertension. Hypertension 2002;40:892–6.
Owens P, Atkins N, O’Brien E. Diagnosis of white coat hypertension by ambulatory blood pressure monitoring. Hypertension 1999;34:267–72.