A challenge test distinguishes primary from secondary hyperaldosteronism on the basis of renin levels. The test is performed with the patient in both the recumbent and upright positions and after the patient has been maintained on a low-sodium diet. In normal persons and in those with essential hypertension, renin concentration is increased by the reduction in volume due to sodium restriction and the upright position. In primary aldosteronism, volume depletion does not occur, and renin concentration remains low.
Admit the patient to the hospital for this test. On admission, obtain and record the patient’s weight.
Ensure the patient follows a reduced-sodium diet supplemented with potassium for 3 days, along with diuretic agents (e.g., furosemide, chlorothiazide), as ordered.
Weigh patient again on the third day, record data, and ensure that the patient remains upright for 4 hours and participates in normal activities.
Obtain a venous heparinized blood sample for renin at 11:00 a.m., when renin is usually at its maximum level. Label the specimen with the patient’s name, date and time of collection, and test(s) ordered. Place the specimen on ice and send it immediately to the laboratory in a biohazard bag.
Interpretation of Renin Stimulation Test
In healthy persons and most hypertensive patients, the stimulation of a low-salt diet, a diuretic agent, and upright posture will raise renin activity to very high levels and result in weight loss. However, with primary aldosteronism, the plasma level is expanded and remains so. In these patients, there is little if any weight loss, and the renin level is very low or undetectable. A response within the normal range can occur in the presence of aldosterone.
Pretest Patient Care
Explain test purpose and procedure. The purpose of the preparation is to deplete the patient of sodium.
Check with individual laboratory for specific practices.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.
Posttest Patient Care
Have patient resume normal activities.
Review test results; report and record findings. Modify the nursing care plan as needed. Counsel appropriately regarding hypertension.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.