What is the protocol for a fludrocortisone (Florinef) suppression test to diagnose primary aldosteronism?

Fludrocortisone Suppression Test Protocol for Primary Aldosteronism

The fludrocortisone suppression test (FST) protocol involves administering fludrocortisone 0.1 mg every 6 hours for 4 days along with oral salt loading, followed by measurement of upright plasma aldosterone levels to confirm primary aldosteronism when levels fail to suppress below the threshold value. 1

Standard Protocol

The standard fludrocortisone suppression test protocol consists of:

1. Preparation:

   • Patient should be on a high-sodium diet (200 mEq/day) prior to and during the test 2
   • Potassium levels should be monitored and supplemented as needed to maintain normal range

2. Administration:

   • Fludrocortisone dose: 0.1 mg orally every 6 hours (total 0.4 mg daily) for 4 days 1, 3
   • Concurrent oral salt loading during the test period
   • Maintain adequate potassium levels throughout testing

3. Monitoring:

   • Measure baseline plasma aldosterone and renin levels before starting fludrocortisone
   • Monitor blood pressure and serum potassium daily during the test
   • Watch for hypokalemia, which is a common complication requiring supplementation

4. Sampling and Interpretation:

   • On day 4, measure upright plasma aldosterone levels at 10 AM 4
   • Positive test: Failure of aldosterone to suppress below 165 pmol/L (approximately 6 ng/dL) 4, 3
   • This confirms the diagnosis of primary aldosteronism

Clinical Considerations

• Medication Adjustments: Medications that affect the renin-angiotensin-aldosterone system should be discontinued before testing:

  • Spironolactone, eplerenone: at least 4-6 weeks prior
  • ACE inhibitors, ARBs, diuretics: at least 2 weeks prior
  • Beta-blockers, central alpha-2 agonists: at least 1 week prior

• Safety Precautions:

  • Regular monitoring of blood pressure is essential as sodium loading may exacerbate hypertension
  • Potassium levels must be checked daily and supplemented aggressively if low
  • The test should be performed in an inpatient setting for patients with severe hypertension or heart failure

• Alternative Testing:

  • If FST is not feasible, seated saline suppression testing (SSST) offers a reliable alternative with high sensitivity (87%) and specificity (94%) 3
  • SSST is less complicated and less expensive than FST while maintaining diagnostic accuracy 3

Comparative Effectiveness

• FST is generally considered the gold standard confirmatory test for primary aldosteronism 1, 5
• Seated saline suppression testing (SSST) has emerged as a reliable alternative with comparable diagnostic accuracy 3
• SSST is more sensitive than recumbent saline suppression testing (RSST), particularly for posture-responsive forms of primary aldosteronism 4, 3

Potential Complications

• Hypokalemia (most common) - requires close monitoring and supplementation
• Worsening hypertension due to salt loading
• Fluid retention and edema
• Headache and dizziness

The fludrocortisone suppression test remains an important diagnostic tool for confirming primary aldosteronism, particularly in cases where the diagnosis remains uncertain after initial screening with aldosterone-to-renin ratio.