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Related Subjects: |Ferritin |CEA |ESR |CRP |ALP |LDH |HbA1c |Alpha Fetoprotein |Anti-Hu ab |Biochemical Lab values

Related Subjects: |Adrenal Physiology |Primary hyperaldosteronism (Conn's syndrome)

Stop Spironolactone, calcium channel blockers, ACE inhibitors and Angiotensin receptor blockers 6 weeks before taking sample, if clinically possible.

About

• Aldosterone: renin ratio is useful in investigating hypertension due to Conn's syndrome
• The renin-aldosterone axis is primarily regulated by renal blood flow.
• Patients should be normally hydrated and have an adequate oral intake of sodium.
• Significant hypokalaemia must be avoided since this suppresses aldosterone secretion
• Please contact the duty biochemist for details of required patient preparation before performing this investigation.

Indications

• Hypertension and hypokalaemia (not diuretic-induced)
• Resistant hypertension
• Adrenal incidentaloma and hypertension
• Severe hypertension (SBP>160 mmHg, DBP>100 mmHg)

Plasma Renin Activity

• Plasma Renin Activity is sometimes assayed on its own, for example, in a patient with known congenital adrenal hyperplasia or Addison's who is being monitored for adequacy of mineralocorticoid replacement.

Normal value

• Aldosterone Upper limit is 630pmol/L. Measured in serum with renin
• Renin: Recumbent: 1.1 - 2.7 pmol/mL/h. 30 min
• Renin: Upright: 2.8 - 4.5 pmol/mL/h
• Renin: Ref range for samples taken randomly: 0.5 - 3.5 pmol/mL/h

Preparation

• It is best to take samples for renin and aldosterone estimation under standard conditions. The hormone measurements will not be made unless the following conditions are adhered to or modified after discussion - contact the Duty Biochemist.
• Discontinue spironolactone and amiloride at least 2 weeks before measurement. Other antihypertensive drugs can make interpretation difficult and ideally should also be discontinued. However, some useful information may be derived from testing in patients taking ACE inhibitors, diuretics, beta-blockers and ARBs (see 6.0)
• Low serum potassium levels can inhibit aldosterone secretion, and ideally, the serum potassium should be not less than 3.5 mmol/L at the time of analysis. Potassium supplements should be used to achieve this level, but these should be discontinued 12 hours before blood sampling.
• Ensure a normal diet with adequate sodium intake has been taken in the few days before sampling
• The patient should be seated for 30 minutes before blood sampling. A change in posture may cause a rise in aldosterone levels (false-positive result) or a rise in renin levels (false negative).
• Venous blood specimens are then taken and transported IMMEDIATELY to the Biochemistry Department. Do not use ice for transportation as this may cause cryoactivation of renin. It would be best if you phoned the lab to say the specimens are arriving.
• ACE inhibitors, ARBs and diuretics may “falsely elevate" plasma renin activity; therefore, the finding of normal aldosterone: renin ratio would not exclude the diagnosis of primary aldosteronism. However, a low plasma renin activity in such circumstances means primary aldosteronism is highly suspect.
• Adrenergic inhibitors (e.g. beta-blockers and central alpha 2 agonists) suppress renin more than aldosterone and may cause a falsely elevated ratio. Elevated aldosterone, with an elevated ratio, means primary aldosteronism remains suspect in such patients.

Sample requirements

• Please note that all samples must remain at room temperature (do not chill) and be sent immediately to the laboratory.
• For adults, blood taken into a 4ml EDTA Tube

Interpretation

• Aldosterone (pmol/L) to renin (mIU/L) ratio of greater than 35 where the aldosterone is greater than 300pmol/L suggests primary aldosteronism (100% sensitivity, 93% specificity).