Additional Specimen Information
Pre-Testing Requirements:
Patient's posture, salt intake, drug therapy, age and time of sampling affect levels. Potassium depletion and/or hypokalaemia lower renin - aldosterone secretion.
Outpatients are best screened as follows: If possible stop non-essential anti-hypertensives for 2 weeks before sampling. Many hypotensive drugs alter renin - aldosterone levels; preferred agents are Alpha-blockers (Doxazosin, Prazosin) and non-dihydropyridine calcium channel blockers (Verapamil, Diltiazem) since they do not greatly alter renin - aldosterone. Screening tests for primary hyperaldosteronism and related conditions can still be done in patients on betablockers, ACE inhibitors and/or diuretics, BUT interpretation must allow for the potent effects these drugs have on the renin - aldosterone axis. Patients should attend (non-fasting) prior to 10.00 am for "ambulant sampling of plasma aldosterone and renin. It is usually wise to check plasma Na, K and creatinine at the time of sampling.
Inpatients are screened as above and should be ambulated for at least 30 minutes before sampling.
Other protocols involving plasma aldosterone/renin measurement include saline suppression (2L saline over 4 hours), 4-hour posture test (08.00 overnight supine aldosterone, repeated after 4 hr of upright posture) and tests using ACTH stimulation or dexamethasone suppression.
If patient is on high dose Biotin therapy (>5 mg/day), wait until at least 8 hours after last dose to take blood sample.
Specimen Collection Protocols:
EDTA blood collected and centrifuged at room temperature. Plasma stored and transported deep-frozen. Whole blood EDTA is stable for 8 hours at room temperature. Separated EDTA plasma is stable for 5 days at room temperature.
Thawed samples will not be assayed. If Renin or Aldosterone-Renin ratio is required, preferably collect blood before 10 am.
For Renin alone collect 1.5 ml (paediatric 1.2 ml).
Deliver to lab immediately.
