Liposomal Amphotericin B Interferes with the Phosphorus Assay on the Synchron LX 20 Analyzer

Abstract

We report an interference caused by liposomal amphotericin B (AmBisome, Astellas Pharma) in the Synchron LX 20 (Beckman Coulter) phosphorus assay (PHOSm). Two inpatients treated with liposomal amphotericin B for invasive mucormycosis were noted to have significantly increased serum phosphorus concentrations. Serum phosphorus values from patient A ranged from 0.9 mmol/L to 3.1 mmol/L compared with pretreatment values of 0.7 to 0.9 mmol/L (reference interval, 0.8–1.5 mmol/L). Patient B was transferred to our institution after 23 days of amphotericin treatment and had phosphorus values ranging from 1.4 to 3.9 mmol/L. Both patients had slightly increased but stable serum creatinine concentrations (53.0–185.6 μmol/L) and did not exhibit symptoms of hyperphosphatemia. One attending physician suspected a possible interference in the phosphorus assay and contacted the clinical laboratory to initiate investigation. In contrast to the markedly increased phosphorus values from the Synchron LX20 analyzer, the …