Discordant plasma phosphorus concentrations (Table 1) were obtained with 2 clinical instruments (concentration range, 4.5–23.8 mg/dL; reference interval, 2.5–4.6 mg/dL) for a 50-year-old woman. Her medical history was positive for idiopathic pulmonary arterial hypertension, chronic kidney disease (stage 1), severe right heart failure, ascites, and thrombocytopenia. During hospitalization, the patient received enteral feeding, cefuroxime, docusate, dronabinol, gabapentin, metolazone, nafcillin, and morphine. 

  • a Reference interval, 2.5–4.6 mg/dL. None of the samples were icteric, lipemic, or hemolyzed.
  • b Timed-rate absorption method; interferents include rifampin and amphotericin B.
  • c Preblanked-sample method; reaction measured at 340 nm. 


  1. In what clinical settings can increased plasma phosphorus be seen?
  2. What methodology is used to measure plasma phosphorus?
  3. What preanalytical factor may be responsible for the discordant phosphorus results?

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