Pseudohyperphosphatemia associated with high-dose liposomal amphotericin B therapy.
BACKGROUND
Acute increases in serum inorganic phosphorus (Pi) up to 4.75 mmol/l in the absence of hypocalcemia and tissue deposition of calcium phosphate were noted in 3 patients receiving liposomal amphotericin B (L-AMB). We investigated L-AMB as a possible cause of pseudohyperphosphatemia.


METHODS
Serum samples from the index patient were analyzed for Pi content by our laboratory's primary analyzer (Synchron LX20) and by an alternate analyzer (Vitros). Clear and lipemic serum pools, and normal saline, were spiked with L-AMB and analyzed by the LX20 Pi method. Ultrafiltration studies were performed on patient and spiked sera.


RESULTS
Increased Pi values were obtained only from the LX20 analyzer. There was a direct linear relationship between the concentration of L-AMB in the spiked samples and the LX20 Pi results, indicating a 0.9 mmol/l Pi increase for every 100 mg/l increase in L-AMB. Ultrafiltration normalized the Pi results.


CONCLUSIONS
Serum Pi results may be falsely increased in patients receiving L-AMB when measured by the LX20 analyzer. This novel cause of pseudohyperphosphatemia is due to interference of L-AMB with the method and is corrected by ultrafiltration of the specimen. Since the LX20 analyzer is widely used by the clinical laboratories clinicians and laboratory personnel should recognize this interference in order to avoid unnecessary diagnostic procedures and interventions.
Lane
Jason W
JW
Microbiology Service, Department of Laboratory Medicine, W. G. Magnuson Clinical Center, NIH, Bethesda, Maryland, USA.
Rehak
Nadja N
NN
Hortin
Glen L
GL
Zaoutis
Theoklis
T
Krause
Philip R
PR
Walsh
Thomas J
TJ
D000666:Amphotericin B / Q000008:administration & dosage / Q000009:adverse effects*; D000935:Antifungal Agents / Q000008:administration & dosage / Q000009:adverse effects*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D008081:Liposomes; D008875:Middle Aged; D010710:Phosphates / Q000097:blood*
D000935:Antifungal Agents; D008081:Liposomes; D010710:Phosphates; D000666:Amphotericin B