Which lab may remain elevated after dialysis?

• A. Blood Urea Nitrogen
• B. Potassium
• C. Creatinine
• D. Phosphate

Answer: (D)

The key idea is that phosphate behaves differently from other waste products during dialysis. During a dialysis session, the process effectively removes many small solutes from the blood, so substances like urea and creatinine drop as they diffuse out. Potassium is also cleared during the session, though it can rise again if intake is high or dialysis isn’t frequent enough. Phosphate, however, is largely stored in bone and within cells. Because of these tissue stores, phosphate is not as readily removed, and after the dialysis session ends, phosphate can move back into the blood from these reservoirs. This redistribution causes a postdialysis rebound in phosphate levels, so phosphate may remain elevated even after dialysis. Therefore, phosphate is the lab most likely to stay elevated following a dialysis session.