🧪 1. VMA (Vanillylmandelic Acid) – 24-Hour Urine

• What it tests:
  Measures the end-product of catecholamine metabolism (epinephrine & norepinephrine) in urine.
• Why it's done:
  To detect pheochromocytoma (adrenal tumor) or neuroblastoma (in children).
• How it works:
  Catecholamines are broken down into metanephrines → then further to VMA, which is excreted in urine.
• Interpretation:
  • High VMA = Possible pheochromocytoma, neuroblastoma, stress, or stimulant intake
  • Requires 24-hour urine sample for accurate analysis

🧪 2. Aldosterone (Serum or 24-Hour Urine)

• What it tests:
  Aldosterone is a hormone from the adrenal cortex that regulates salt and water balance.
• Why it's done:
  • Evaluate primary aldosteronism (Conn’s syndrome)
  • Investigate hypertension with low potassium levels
• Interpretation:
  • High aldosterone + low renin = Primary hyperaldosteronism
  • Low aldosterone + low renin = Possible secondary causes (e.g., Cushing’s, renal artery stenosis)
• Note:
  Must often be interpreted alongside renin levels and corrected for potassium and sodium intake

🧪 3. Catecholamines (Adrenaline & Noradrenaline – 24-Hour Urine)

• What it tests:
  Measures adrenaline (epinephrine) and noradrenaline (norepinephrine) in urine over 24 hours.
• Why it's done:
  Diagnoses catecholamine-secreting tumors like:
  • Pheochromocytoma (adrenal medulla)
  • Paraganglioma (extra-adrenal)
• Interpretation:
  • Elevated levels → Strong indicator of such tumors
  • Levels fluctuate, hence 24-hour collection improves accuracy
• Symptoms to test for:
  • Severe hypertension, headaches, palpitations, sweating, anxiety, tremors

🩸 4. Plasma Renin Activity (PRA)

• What it tests:
  Measures renin enzyme activity in the blood, which regulates blood pressure via the RAAS system (Renin–Angiotensin–Aldosterone System)
• Why it's done:
  • Investigate secondary hypertension, especially in:
    • Renovascular hypertension
    • Primary aldosteronism
    • Adrenal tumors
• Interpretation:
  • High PRA + high aldosterone → Secondary hyperaldosteronism (e.g., renal artery stenosis)
  • Low PRA + high aldosterone → Primary aldosteronism (e.g., adrenal adenoma)
• Important:
  • Sample collection requires strict posture and timing protocols
  • Influenced by medications (e.g., beta-blockers, diuretics)

🧪 5. Metanephrine – 24-Hour Urine

• What it tests:
  Measures metanephrine and normetanephrine, which are more stable metabolites of catecholamines.
• Why it's preferred:
  • More sensitive and specific than direct catecholamine or VMA measurement
  • First-line test for pheochromocytoma
• Interpretation:
  • Elevated 24h metanephrines = Strong evidence of pheochromocytoma or paraganglioma
  • Used for both screening and monitoring post-surgery
• Advantages:
  • Less variable than catecholamines
  • Can detect intermittently secreting tumors

✅ When to Order These Tests

🧠 Tips for Accurate Results:

• 24-hour urine: Requires proper timing and refrigeration
• Dietary restrictions before testing:
  • Avoid bananas, vanilla, chocolate, caffeine, and some medications
• PRA and Aldosterone: Follow posture-dependent protocols (supine/resting or upright)