<prompt> Best screening test for pheochromocytoma?Urinary VMA estimationSerum catecholamine estimationClonidine suppression testUrinarymetanephrine  <response>: Ans: a Urinary VMA estimationRef: Vasudevan Sreekumari, 6th edi., Pg. 207Vanillyl mandelic acid VMA in urineVMA is the main urinary metabolite of the norepinephrine pathway. Metanephrine is acted upon by mono amine oxidase to formVMA. Normal level of excretion of VMA is 2-6 mg24 hr.lt is increased in pheochromocytoma and in neuroblastoma.Patient is asked to refrain from intake of chocolate, coffee, banana, vanilla ice creams, citrus fruits lime orange. These items contain vanillin, which produces very high value of VMA in urine. Patient should not take aspirin or drugs containing phenol ring.Homovanillic acid HVA in urine: HVA is the main urinary metabolite of dopa and dopamine pathway It is increased in neuroblastoma, malignant pheochromocytoma and ganglioneuroma.It is useful to predict prognosis of neuroblastoma. Drugs increasing the value are -L-dopa, disulfiram and reserpine. 