Makindo Medical Notes

Related Subjects: |Ferritin |CEA |ESR |CRP |ALP |LDH |HbA1c |Alpha Fetoprotein |Anti-Hu ab |Biochemical Lab values |Adrenal Physiology |Primary hyperaldosteronism (Conn's syndrome)

Renin and Aldosterone Renin Ratio (ARR): Stop Spironolactone, calcium channel blockers, ACE inhibitors, and Angiotensin Receptor Blockers 6 weeks before taking sample, if clinically possible.

About

• The Aldosterone:Renin Ratio (ARR) is essential in investigating hypertension due to Conn's syndrome (primary hyperaldosteronism).
• The renin-aldosterone axis is primarily regulated by renal blood flow.
• Patients should be normally hydrated and have an adequate oral sodium intake prior to testing.
• Significant hypokalaemia should be avoided, as it suppresses aldosterone secretion.
• Consult the duty biochemist for detailed patient preparation guidelines before this investigation.

Indications

• Hypertension with unexplained hypokalaemia (not diuretic-induced).
• Resistant hypertension not responding to standard treatments.
• Presence of adrenal incidentaloma and hypertension.
• Severe hypertension (SBP >160 mmHg, DBP >100 mmHg).

Plasma Renin Activity

• Plasma Renin Activity (PRA) may also be tested alone, particularly in patients with known conditions such as congenital adrenal hyperplasia or Addison's disease, where monitoring mineralocorticoid replacement adequacy is required.

Normal Values

• Aldosterone: Upper limit is 630 pmol/L, measured alongside renin in serum.
• Renin Recumbent (lying down): 1.1 - 2.7 pmol/mL/h
• Renin Upright (standing): 2.8 - 4.5 pmol/mL/h
• Random Sample Reference Range: 0.5 - 3.5 pmol/mL/h

Preparation

• Renin and aldosterone samples should ideally be collected under standardized conditions. Hormone measurements will be deferred unless specified conditions are met. Contact the Duty Biochemist for guidance if any modifications are required.
• Medications: Discontinue spironolactone and amiloride at least 2 weeks before the test. Other antihypertensive medications may interfere and should ideally be stopped if possible.
• Potassium Levels: Ensure serum potassium is above 3.5 mmol/L, as low potassium can inhibit aldosterone. If necessary, potassium supplements can be given to achieve this level but should be stopped 12 hours before sampling.
• Sodium Intake: Patients should maintain a normal diet with adequate sodium intake for a few days before sampling.
• Posture: The patient should be seated for 30 minutes before blood sampling to avoid posture-related false-positive or false-negative results.
• Sample Handling: Venous blood should be drawn and immediately transported to the Biochemistry Department at room temperature (do not use ice, as it may cause cryoactivation of renin). Notify the lab when sending the sample.
• Interference: ACE inhibitors, ARBs, and diuretics can elevate PRA, which may lead to a false negative in primary aldosteronism diagnosis. A low plasma renin activity (PRA) in this context is highly indicative of primary aldosteronism. Adrenergic inhibitors (e.g., beta-blockers) may also falsely elevate ARR.

Sample Requirements

• Keep all samples at room temperature and send immediately to the laboratory.
• For adults, blood should be collected in a 4ml EDTA Tube.

Interpretation

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