From the Guidelines
A saline suppression test is a diagnostic procedure used to evaluate patients with suspected primary aldosteronism, where the patient receives an intravenous infusion of normal saline at a rate of 500 mL per hour for 4 hours while in a seated position. The test is used to confirm the diagnosis of primary aldosteronism, a condition where the adrenal glands produce too much aldosterone hormone. During the test, blood samples are collected before and after the infusion to measure aldosterone and renin levels. In normal individuals, the increased sodium load should suppress aldosterone production, typically to levels below 5-10 ng/dL. However, in patients with primary aldosteronism, aldosterone levels remain elevated despite the saline infusion because the excess production occurs independently of the body's regulatory mechanisms. Some key points to consider when performing a saline suppression test include:
- Patients should discontinue certain medications like diuretics, ACE inhibitors, ARBs, and beta-blockers for 2-4 weeks before the test, as these can affect results 1, 2.
- Potassium levels should be normalized before testing 1, 2.
- The test is usually performed in the morning, and patients should remain seated during the procedure to minimize postural effects on hormone levels.
- The saline suppression test helps differentiate primary aldosteronism from other causes of hypertension and guides appropriate treatment decisions 1, 2, 3. It's worth noting that the saline suppression test is just one part of the diagnostic workup for primary aldosteronism, and other tests such as adrenal vein sampling and imaging studies may also be necessary to confirm the diagnosis and guide treatment 1, 2, 4.
From the Research
Definition and Purpose of Saline Suppression Test
- The saline suppression test (SST) is used to confirm the diagnosis of primary aldosteronism (PA) 5, 6, 7, 8, 9.
- It serves to distinguish between unilateral and bilateral PA, with the goal of identifying patients who can bypass adrenal vein sampling (AVS) and proceed directly to medical treatment 5, 6.
Procedure and Interpretation
- The test involves measuring plasma aldosterone concentration (PAC) and aldosterone-to-renin ratio (ARR) before and after infusion of saline solution 5, 6, 7, 8.
- A reduction in ARR and PAC < 300 pmol/L after the test can predict bilateral PA with high specificity 5, 6.
- Seated SST (SSST) may be more sensitive than recumbent SST (RSST), especially for posture-responsive PA 7.
- The diagnostic cutoff for SSST using immunoassay is different from that using high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS) 8.
Clinical Applications
- The SST can help identify patients with bilateral PA who can be treated medically without the need for AVS 5, 6.
- The test can also help diagnose PA in patients with inconclusive fludrocortisone suppression testing (FST) results 7.
- The use of SST in clinical practice can improve the diagnosis and treatment of PA, and reduce the need for invasive procedures like AVS 9.