Fludrocortisone Suppression Test Interpreter

Aldo @ 10AM (ng/dL)

Serum Sodium

Serum Potassium

The FST protocol requires fludrocortisone (0.1 mg every 6 hours) and high sodium intake for 4 days. If serum K+ is < 3.0 mEq/L, the test result is invalid as hypokalaemia itself suppresses aldosterone.

Guidelines & Evidence

Verified

Last Review: 2026

When to Use

Confirmatory testing in patients with high screening ARR (Aldosterone-to-Renin Ratio).

When salt loading test is contraindicated or inconclusive.

Identifying autonomy of aldosterone production in Primary Aldosteronism (PA).

Clinical Pearls

Diagnostic Thresholds

Aldo (ng/dL)	Interpretation
> 6.0	Positive (PA Confirmed)
< 6.0	Negative (Excludes PA)

Potassium Caveat

Hypokalaemia is a potent inhibitor of aldosterone secretion. If a patient is hypokalaemic during the test, they may "pseudo-suppress" their aldosterone, leading to a false-negative result. Aggressive potassium supplementation is essential during the 4-day protocol.

Last Comprehensive Review: 2026

Recent Journal Updates

Cancer MedicineJul 22, 2026

Analysis of Age, Period and Cohort Trends in Cervical In Situ and Invasive Carcinomas for Assessing the Utility of Screening Approaches—Results From the Saarland Cancer Registry

Clinical Context

We think this has broad domain relevance to Fludrocortisone Suppression Test.

JAMAJul 21, 2026

Correction to Primary Composite Outcome in a Trial of Transfusion Strategy

Clinical Context

We think this has broad domain relevance to Fludrocortisone Suppression Test.

Tropical Med & Intl HealthJul 7, 2026

Virological Suppression Rate and Drug Resistance in Children and Adolescents Receiving Dolutegravir‐Containing Antiretroviral Therapy in Ndop Health District, Cameroon

Clinical Context

We think this might be relevant to the clinical guidance for Fludrocortisone Suppression Test.

Fludrocortisone Suppression Test Interpreter

When to Use

When to Use

How it Works

Standard FST Procedure

Clinical Pearls

Diagnostic Thresholds

Potassium Caveat

The Evidence

Guidelines

The management of primary aldosteronism: case detection, diagnosis, and treatment: an Endocrine Society Clinical Practice Guideline.

Recent Journal Updates

Fludrocortisone Suppression Test Interpreter

When to Use

When to Use

How it Works

Standard FST Procedure

Clinical Pearls

Diagnostic Thresholds

Potassium Caveat

The Evidence

Guidelines

The management of primary aldosteronism: case detection, diagnosis, and treatment: an Endocrine Society Clinical Practice Guideline.

Recent Journal Updates