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If the renal stone size is 4mm or less, it will come out in its own by drinking plenty of water and if it more than 7mm, it should be removed or crushed by ESWL
and if it is between 5 and 6 mm it may or may not come out. He should be drinking Plenty of water, if it doesn't help he can opt for Endoscopic Shock
(ESWL) after discussing it with his Urologist
Take him to a Urologist at the earliest.