A 10-year-old child presents with hypertension, tachycardia, nervousness and sweating. The best initial diagnostic evaluation is which of the following?

d. Measurement of catecholamines and their degradation products in a 24-hour urine specimen

The first diagnostic step in determining the functional state of an adrenal gland or lesion is to screen the urine or plasma for secretory products. Once hypersecretion is demonstrated, the specific type of pathology producing a syndrome must be determined with the aid of functional tests and relevant scanning and imaging. The most efficient and sensitive means of screening in a patient suspected of having a pheochromocytoma, (as indicated here) is measurement of the catecholamines or metabolic products thereof in the urine. Although 24-hour samples can smooth out the possible episodic variations in catecholamine secretion, shorter sampling periods can be useful, especially if corrected for creatinine excretion. Timing of the collection is critical in patients who have only episodic hypertension. Urine collection should be started immediately after a suspected attack of hypertension. Fluctuations in plasma catecholamine concentrations are much greater than those in urinary excretion, even in normal subjects. Plasma determinations are quite sensitive and specific with radioimmunoassays and HPLC determination of plasma catecholamines, but the specificity can be low because of the overlap of normal spikes in catecholamine concentrations with concentrations produced by minimally secreting pheochromocytomas. MRI and MIBG imaging studies are both potentially useful after catecholamine excess is confirmed. MRI demonstrates anatomy quite well. MIBG scintigraphy is particularly useful in looking for nonadrenal and bilateral pheochromocytomas.