A very rare cause of high blood pressure is a tumor of the adrenal gland called a pheochromocytoma. Patients with this tumor experience high blood pressure that comes and goes, and symptoms that include dizziness, sweating, and heart palpations. These patients may have also experienced a sudden loss of weight. All of these symptoms are due to the abnormal release of the hormone epinephrine from the adrenal gland. Removal of the tumor usually relieves all of the symptoms, including the hypertension.

The means of detecting the tumor is by looking for the excess hormone or its by-products. Because secretion of the hormone may not be constant, the best way to look for it is using a 24-hour urine collection. If, at any time during those 24 hours, there has been an excess secretion of epinephrine, it will be excreted through the kidneys in the form called metanephrine. Testing for this substance in the urine will reveal an elevated level if a pheochromocytoma is present.