The nurse is assessing a client who has a history of kidney stones and returns to the clinic with flank pain. Which intervention should the nurse implement first?

A. The first step in managing pain is assessing its severity, and using a standard pain assessment scale is the best way to measure the client's pain intensity objectively. B. Asking about home pain medication use is important but should be done after assessing the pain intensity. C. Observing nonverbal signs of pain can be helpful, but it should not replace the use of a standardized pain scale. D. Straining the urine to check for calculi can be done later but is not the immediate priority when the client presents with flank pain.