Interference of hydroxyphenylpyruvic acid, hydroxyphenyllactic acid and tyrosine on routine serum and urine clinical chemistry assays; implications for biochemical monitoring of patients with alkaptonuria treated with nitisinone

We have assessed the effect of elevated concentrations of hydroxyphenylpyruvic acid (HPPA), hydroxyphenyllactic acid (HPLA) and tyrosine, on a range of chemistry tests in serum and urine to explore the potential for chemical interference on routine laboratory analyses in patients with alkaptonuria (AKU) treated with nitisinone and similarly implications for patients with hereditary tyrosinemia type 1 (HT-1). HPPA, HPLA and tyrosine were added separately to pooled serum from subjects without AKU in a range of assays with Roche Modular chemistries. Effects on urine were assessed by changes in urine strip chemistries after mixing a positive control urine with various amounts of the test compounds and reading on a Siemens urine strip meter. No significant effect (p > 0.1) was observed up to 225 μmol/L of HPPA and HPLA, and up to 5000 μmol/L tyrosine, on any of the serum-based assays including those with peroxidase-coupled reaction systems of enzymatic creatinine, urate, total cholesterol, HDL cholesterol and triglyceride. Both the monohydroxy HPPA, and the dihydroxy homogentisic acid (HGA), at increased urine concentrations typical of nitisinone-treated AKU and non-treated AKU respectively, did however show marked negative interference in strip assays for glucose and leucocytes; i.e. those with peroxide-linked endpoints. The effect of increased HPLA was less marked. In patients with AKU or on nitisinone treatment and HT-1 patients on nitisinone, urine strip chemistry testing should be used sparingly, if at all, to avoid false negative reporting. It is recommended that urine assays should be organised with a suitable specialist laboratory. •Alkaptonuria treated with nitisinone results in reduction of HGA and marked increases in HPPA, HPLA, and tyrosine•The elevated concentrations of HPPA, HPLA and tyrosine did not interfere with a wide range blood/serum assays used in clinical practice•Increased urinary HGA and HPPA interfered with some urine test strip chemistries•The oxidase-based urine assays showed most suppression of response by HGA and HPPA•Urine strip tests should be avoided in patients with alkaptonuria and patients on nitisinone