Recent tPA administration can cause pseudo-hyperargininemia and may mimic arginase deficiency or arginine supplementation.

Individuals suspected of or diagnosed with a rare disorder, including inherited metabolic disorders (IMD), often need frequent and/or urgent vascular access for blood draws and treatment, making central indwelling catheters commonly used devices in this patient population. These indwelling catheters are prone to thrombosis, limiting vascular access. This complication is frequently resolved with the use of altepase, a recombinant tissue plasminogen activator (tPA). This report describes two individuals, one with a known IMD and one undergoing evaluation for an IMD, who were found to have hyperargininemia (>500 μM; reference 10-140 μM) by plasma amino acid (PAA) analysis of a specimen collected ~1.5-3 h after clearance of an indwelling catheter with tPA. In both cases, hyperargininemia resolved with repeat testing, suggesting pseudo-hyperargininemia secondary to tPA administration. Quantitative amino acid analysis of the administered tPA demonstrated an arginine level of ~200 mM, supporting tPA as the cause of pseudo-hyperargininemia. Certain formulations of tPA contain high concentrations of arginine, which if not cleared properly can result in marked elevations of arginine, mimicking arginase deficiency or suggesting arginine supplementation. Thus, the possibility of pseudohyperargininemia due to tPA administration should be considered when obtaining PAAs from an indwelling catheter in any individual being evaluated or managed for an IMD.