3 mL (2.5 mL min.) Plasma from 1 Lavender Top (EDTA) tube. Patient should be ambulatory / upright 2 hours prior to the test. Separate plasma and freeze. Ship frozen. Drug interactions to be noted: Potassium wasting diuretics, Spironolactone, Eplerenone, Amiloride and Triamterene should be discontinued at least for 4 weeks; Adrenergic blockers, Clonidine, Methyldopa, NSAIDs, Angiotensin-converting enzyme inhibitors, Angiotensin receptor blockers, Renin inhibitors and Dihydropyridine calcium channel antagonists should be discontinued for 2 weeks. If necessary to maintain hypertension control, patients should be treated with other antihypertensive medications like Verapamil slow-release, Hydralazine, Prazosin, Doxazosin & Terazosin that have lesser effects on Plasma renin & aldosterone levels. Any change in medication should be done in consultation with treating physician.