A Modified Saline Suppression Test to Confirm the Diagnosis of Primary Aldosteronism

Presentation Number: SAT-59
Date of Presentation: June 15th, 2013

Mitra Lynn Rauschecker*1, Andreas G. Moraitis2, Charalampos Lyssikatos3, Elena Belyavskaya4, Smita Baid Abraham5 and Constantine A Stratakis3
1NIH, Bethesda, MD, 2NICHD/NIH, Bethesda, MD, 3National Institutes of Health (NIH), Bethesda, MD, 4Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), National Institutes of Health (NIH), Bethesda, MD, 5Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD

Abstract

Background:  Confirmatory testing is necessary to make the diagnosis of primary aldosteronism (PA).  However, the available sensitivity and specificity data on these tests is limited and each has technical challenges (1). The two most commonly performed tests are the normal saline suppression test (SST) and the oral salt load test (OST).  In the SST, it is not infrequent to see false negative results.  In the OST, it is difficult to attain a 24-hour urine sodium level >200 mmol/24-hr.  We evaluated the accuracy of the SST, OST, and a “modified SST” (MSST).

Methods: Patients were suspected of having PA on the basis of an elevated aldosterone/plasma renin activity ratio (ARR). Confirmatory testing was performed. During the SST, patients received 2 L normal saline over four hours (hr).  Plasma aldosterone levels were collected hourly. A plasma aldosterone value of >10 ng/dl after 4 hr of saline infusion was considered positive for PA. For the OST, patients received 2 grams NaCl three times a day for three days, and on the third day, performed a 24-hr urine collection for aldosterone and sodium. Urine aldosterone (UA)>12 mcg/24-hr with a urine Na (UNa)>200 mmol/24-hr was considered positive. For the MSST, a 24-hr urine collection for aldosterone and sodium was collected starting on the day of the SST; UA>12 mcg/24-hr with a UNa>200 mmol/24-hr was considered positive, as with the OST.

Results: Six PA patients underwent SST, OST, and MSST. Four of six patients had negative SST. Of those four patients, two patients had a positive OST, while all four patients had a positive MSST. Of the two patients without a positive OST, the test was uninterpretable, as UNa was not >200 mmol/24-hr, while all four patients with positive MSST had UNa>200 mmol/24-hr. Patients with an uninterpretable OST and negative SST will undergo repeat OST to confirm the diagnosis.

Conclusion: We demonstrate that the MSST may be an alternative to OST and SST in the diagnosis of PA. The benefits of the MSST include ease for patients, as no oral salt tablets are required. Additionally, MSST appeared to have fewer false negative results as compared with SST.

 

Nothing to Disclose: MLR, AGM, CL, EB, SBA, CAS