QUESTION--I am interested in testing a young patient with possible POTS for his aldosterone response with stimulation testing. I cannot find any formal protocol to do this except for brief mentions of using lasix and prolonged standing. Could you help me with deliniating more clear steps? For example, 2 hour standing + lasix 20mg PO with expected 2-4x rise in Aldo or maybe just 3 hours standing?  Natalia  Regales
The upright posture test is a physiologic stimulus to plasma renin activity (PRA) and  subsequently the plasma aldosterone response to activation of the RAS.  The response is amplified by volume depletion, either acute by diuretic administration or chronic by a low dietary sodium intake. I would not use lasix pre-treatment in a patient with POTS since you might amplify the tachycardic response.
The standard posture test would be to measure PRA and plasma aldostereone, first recumbent and then after 90-120 minutes of upright posture (ambulating in the clinic environment. If you chose to amplify the response with a diuretic, 20-40 mg lasix is given 2 hours before the recumbent values are obtained. The usual response is a two fold increase (or more) of both PRA and plasma aldosterone.   Robert Dluhy,  MD