Which laboratory value above the reference range most clearly indicates hyperphosphatemia in CKD?

• A. Calcium 9.2 mg/dL
• B. Phosphorus 5.5 mg/dL
• C. Sodium 135 mEq/L
• D. Potassium 5.5 mEq/L

Answer: (B)

Hyperphosphatemia is diagnosed by an elevated serum phosphorus level. In CKD, the kidneys lose the ability to excrete phosphate effectively, so phosphate builds up in the blood. A phosphorus value of 5.5 mg/dL is above the normal adult range (about 2.5–4.5 mg/dL) and directly shows hyperphosphatemia. The calcium value is normal, sodium is normal, and potassium is at the higher end but not the indicator of elevated phosphate. Thus, the phosphorus result is the one that clearly reflects hyperphosphatemia.