Additional Specimen Information
Pre-Testing Requirements:
Patient's posture, sodium intake, drug therapy and time of sampling all profoundly alter PRA.
Outpatients are best screened as follows:
If possible stop non-essential drugs for 2 weeks before sampling. Many hypotensive drugs alter renin levels; diuretics and ACE inhibitors increase PRA, whereas Beta-blockers reduce PRA. Alpha-blockers (Cardoxan, Prazosin and related drugs) or calcium channel blockers have less effect and are therefore preferred where the clinical condition allows.
Patients should attend (non-fasting) prior to 10.00 am for “ambulant” sampling for PRA. Plasma aldosterone also usually necessary for interpretation.
Inpatients are also screened as above and should be ambulated for at least 30 minutes before sampling. “Bed bound” patients may be sampled after a similar time in sitting position.
Other protocols involving Angiotensin II measurement include frusemide challenge, 2 hours of quiet standing or response to sodium depleting diets. Consult with an Endocrinologist for indications and test protocols.
Specimen Collection Protocols:
Blood to be taken into 0.15mL of angiotensin inhibitor solution containing 0.125M disodium EDTA, 0.05M o-penanthroline, 0.9% sodium chloride and 2% ethanol, made up in freshly boiled distilled water with 0.2% neomycin sulphate. These tubes are available from Endolab (Phone: internal 80848, external 03-3640848).
On the day of the blood collection thaw the inhibitor cocktail tubes in hot tap water and mix well. Draw a 3ml blood sample with a 5ml syringe and needle and then transfer the blood from the syringe to the AII enzyme cocktail tube. Mix the contents gently with 4 or 5 inversions. Immediately centrifuge the tube, separate the plasma and transfer the plasma to the sample tube (labelled “AII plasma only”) provided. Freeze the plasma immediately (preferably snap frozen on dry ice or liquid nitrogen). The plasma sample should then be transported frozen. Thawed samples will not be assayed.
