Norm of Aldosterone Suppression Test
<5 ng/dL (<0.14 nmol/L SI units).
>10 ng/dL (>0.2777 nmol/L SI units).
Usage of Aldosterone Suppression Test
Definitive diagnosis of primary aldosteronism, which is also common in clients with essential hypertension.
Description of Aldosterone Suppression Test
Aldosterone is a mineralocorticoid secreted by the adrenal cortex that functions in blood pressure and body fluid regulation. It acts on the renal distal tubule, where it increases resorption of sodium and water at the expense of increased potassium excretion. Levels are affected by body position and sodium and potassium levels. The aldosterone suppression test measures aldosterone levels before and after an infusion of saline. In primary aldosteronism, the saline infusion fails to suppress aldosterone levels as much as it suppresses the levels in a normal client.
Professional Considerations of Aldosterone Suppression Test
Consent form NOT required.
Volume overload, hypertension, myocardial ischemia, congestive heart failure.
The serum test is contraindicated in clients with congestive heart failure.
- The client should be positioned upright for 2 hours and then lie in a recumbent position from the onset of the test until the second specimen is drawn at the completion of the infusion.
- Tubes: Two red topped, red/gray topped, gold topped, green topped, or lavender topped for blood test.
- Obtain 2 L of 0.9% saline and a 24-hour urine collection container to which 10 g of boric acid has been added.
- Draw a 2.5-mL blood sample for the baseline aldosterone level.
- Infuse 2 L of normal saline intravenously over a 4-hour period to the recumbent client.
- Draw a final 2.5-mL blood sample for aldosterone level.
- Discard the first morning-urine specimen.
- Collect all urine voided in a 24-hour period in a refrigerated container to which 10 g of boric acid has been added. Include urine voided at the end of the 24-hour period. For catheterized clients, keep the drainage bag on ice and empty the urine into the collection container hourly.
- At the end of 24 hours, mix the urine gently and collect a 100-mL aliquot in a clean container.
- Note the collection site and the time on all laboratory requisitions and blood tubes. For the urine sample, write the total 24-hour urine volume on the laboratory requisition and the aliquot container label.
- Transport each specimen to the laboratory immediately after collection.
Client and Family Teaching
- The test takes several hours. Bring reading material or other diversional item.
- Results are normally available within 24 hours.
Factors That Affect Results
- Reject hemolyzed specimens.
- Radioactive scans within 7 days before urine collection invalidate results.
- Cimetidine, but not omeprazole, inhibits test results.
- Insulin resistance occurs with primary hyperaldosteronism.