Spurious hyperphosphatemia related to severe hyperbilirubinemia in patients with end-stage liver disease

Aim: Accurate assessment and management of hyperphosphatemia is a key component of the care of patients with both acute and chronic kidney disease (CKD). In some cases, hyperphosphatemia may be spurious, and failure to recognize this may lead to complications. We report 6 cases of spurious hyperphosphatemia in patients with end-stage liver disease (ESLD) that was associated with severe hyperbilirubinemia. Methods: Six patients with ESLD and severe hyperbilirubinemia were found to have high serum phosphorus (PO4) using our Beckman Coulter Synchron LX20 or DxC analyzers. Samples were sent to an affiliated hospital that uses the Roche Integra analyzer, for evaluation to rule out spurious elevations of serum phosphorus. We also measured serum levels of parathyroid hormone (PTH), calcium, creatinine, total protein, and total bilirubin. Data were analyzed by t-test. Results: Mean serum PO4 using the Beckman analyzers was 7.5 mg/dL (SD +/- 1.98); using the Roche Integra analyzer it was 4.0 mg/dL (SD +/- 0.44) (mean difference = 3.5 mg/dL; p = 0.0017). Mean PTH and calcium levels were 43 pg/mL and 9.1 mg/dL, respectively. Mean total bilirubin level was 27.9 mg/dL and mean total protein was 6.0 g/dL. Conclusion: The Beckman LX20 and DxC analyzers use time-dependent photometric methods to measure serum PO4 which can be affected by hyperbilirubinemia. In contrast, the Roche Integra analyzer uses an endpoint photometric method with sample blanking, which helps to correct for the effect of hyperbilirubinemia. Clinicians managing patients with marked hyperbilirubinemia should consider spurious laboratory abnormalities.