Spurious Hyperphosphatemia in Two Children With End-Stage Renal Disease: A Case Report

Spurious hyperphosphatemia, also known as pseudo-hyperphosphatemia, refers to artifactually elevated serum phosphate values that do not correspond to their actual systemic levels. Vascular access poses a significant challenge for individuals undergoing hemodialysis (HD) due to chronic kidney disease, primarily attributed to the elevated incidence of complications, such as infections or thrombosis associated with catheter use. To mitigate clotting risk during the inter-dialysis intervals, in recent years, a strategy involving the application of concentrated heparin (recombinant tissue plasminogen activator (rt-PA) e.g. alteplase) has been used. These infusions have a very high content of phosphorus, and if it is not removed sufficiently before collecting blood samples through the central venous catheter, it can cause erroneously high phosphate levels. Here we report two cases of pseudo-hyperphosphatemia caused by contaminated blood samples obtained from an HD catheter from the pediatric nephrology department. Absurd values found in routine samples led us to investigate the reason for these results. Further investigations carried out by the laboratory biochemistry department showed that all the analytical checks and proficiency testing performance were within acceptable limits. We hypothesized that there was a pre-analytical error such as possible contamination with the high phosphate content of heparin and alteplase solution in the catheter, contributing to the increased phosphate levels in these samples.