Hi there, I am Dr. Deepak, I work in Emergency Department, where I see many of my patient who come after head injury. As you have mentioned your friend had a slip and fall on the ice. and you took her to an ER and she was worked up for concussion. Its a good thing you asked that doubt regarding the management protocol of ER. I can understand you might be wondering why your friend has to undergo USG for Kidney(actually its for the abdomen) after having head injury. People working in ER they just don t come to conclusion that you have head injury, They follow something that is called ATLS (Advanced Trauma Life Support). In it Doctor s are suppose think of all the patient s who come following trauma (accident, even a fall is considered as accident) as the worst case they have seen, so they workup there Patient from the condition that kill a patient earlier to the condition which will kill at the last. ATLS also recommends to do an imaging study for abdomen to rule of any occult bleeding into the abdomen. Patient may not have symptoms related to it when she is in the ER. So, they find it safe to do the USG abdomen before they discharge the patient home, as it has no radiation, its cheaper then other imaging study and it takes less amount of time. Thank you, hope your concern was dealt with and hope your friends has a speedy recovery.