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 three 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 laboratorys 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. ? Conclusion: Serum Pi results may be falsely elevated 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.? ? ? ? ? ? Background: Bilirubin's role as a protectant against free radicals has stimulated interest in accurately measuring low and normal serum concentrations of bilirubin. We examined bilirubin photolysis in serum specimens exposed to room lighting in order to determine acceptable times for light exposure of specimens.? Methods: Serum specimens in clear tubes were exposed to laboratory lighting for varying periods of time at room temperature before analysis of total and direct bilirubin on a Synchron LX20 analyzer using diazo reactions.? Results: In serum exposed to room lighting, total and direct bilirubin declined approximately linearly over 24 h. Proportional declines of total bilirubin were greater for normobilirubinemic specimens (about 6%/h) than for hyperbilirubinemic specimens (1-5%/h, depending on bilirubin level). In the dark, total bilirubin was stable, but there was a slow conversion of direct bilirubin (0.5-1%/h) to indirect bilirubin.? Conclusions: Light exposure yields greater proportional degradation of bilirubin for specimens with low and normal bilirubin concentration. Light exposure should be kept to < 2 h to keep errors in bilirubin measurement < 10% due to photolysis.
| Lane, Jason W; Rehak, Nadja N; Hortin, Glen L et al. (2008) Pseudohyperphosphatemia associated with high-dose liposomal amphotericin B therapy. Clin Chim Acta 387:145-9 |
| Rehak, Nadja N; Cecco, Stacey A; Hortin, Glen L (2008) Photolysis of bilirubin in serum specimens exposed to room lighting. Clin Chim Acta 387:181-3 |
