RET and pheochromocytoma: Therefore, the ATA recommends that pheochromocytoma screening (by plasma or 24-hour urine fractionated metanephrines) should begin by age 8 in carriers of RET mutations associated with MEN 2B and mutated RET codons 634 and 630 and by the age 20 years in carriers of other MEN 2A RET mutations.