Pathology tests database

Sample and container requirements

EDTA Plasma

Minimum volume required

500 µL plasma

Special requirements

Samples need to be centrifuged within 24 hours of collection. The plasma should then be separated and stored at -20°C immediately after centrifugation. Samples must NOT be stored in the fridge at any point. Do NOT chill sample collection tubes or store collection tubes on ice. Samples should be transported to the lab at room temperature and received same day.

Patient preparation

Attempt to correct any hypokalaemia and patients should be on a liberal rather than restricted sodium intake. Withdraw the following agents that may affect aldosterone/renin ratio (ARR) for at least 4 weeks: - Spironolactone, eplerenone, amiloride and triamterene - Potassium-wasting diuretics - Products derived from liquorice root (e.g. Confectionary liquorice, chewing tobacco) If the ARR off the above agents are not diagnostic, and if hypertension can be controlled with relatively non-interfering medications, withdraw other medications that may affect the ARR for at least 2 weeks: - Beta-adrenergic blockers, central alpha-2 agonist (e.g. clonidine, alpha-methyldopa), nonsteroidal anti-inflammatory drugs - Angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, renin inhibitors, dihydropyridine calcium antagonists If necessary to maintain hypertension control, commence other hypertensive medications that have a lesser effects on ARR (e.g. verapamil slow release, hydralazine, prazosin, doxazosin, tetrazosin). Establish oral contraceptive (OC) and hormone replacement therapy (HRT) status, as oestrogen containing medications may lower direct Renin concentrations and cause false positive ARR. Do not withdraw OC unless confident of alternative contraception. Blood samples should be drawn in the morning. Please note on the request form the position of the patient at sampling as this will allow the appropriate reference range to be used. The patient should remain recumbent for 15 mins (or more) prior to collection of the supine sample. The patient should be upright for at least 15 mins before the ambulatory sample is taken. For aldosterone/renin ratio, patient needs to be seated for 5-15 minutes before taking blood. Collect blood mid-morning, after the patient has been up (sitting, standing, or walking) for at least 2 hours. Please note on the request form the position of the patient at sampling.

Sample viability

Turnaround time

7 days

Reference range

Ambulatory: Females: 6.1 – 62.7 mIU/L Males: 9.0 – 103 mIU/L Supine: 4.2 – 59.7 mIU/L (Source: Immuno Diagnostic Systems) Screen positive for Conns: Aldosterone/renin ratio >91 pmol/mU + aldosterone >750 pmol/L The Aldosterone/Renin ratio cut – off that we are providing is a guide only and not a diagnostic test and the ratio should be interpreted, cautiously, in conjunction with relevant clinical information and medications that may affect the ratio.

Clinical guidance

Please refer to LabTestsOnlineUK to learn more about renin. https://labtestsonline.org.uk/tests/aldosterone-and-renin

Notes

Haemolysed and lipaemic samples are unsuitable for analysis. Freezing and thawing of plasma samples should be avoided.