Histamine metabolite to basal serum tryptase ratios in systemic mastocytosis and hereditary alpha tryptasemia using a validated LC-MS/MS approach

Abstract Objectives Histamine, mainly produced in mast cells (MC), plays a key role in allergy and inflammation. Measuring its urinary metabolites, N-methylhistamine (NMH) and 1-methyl-4-imidazoleacetic acid (MIMA), is essential in assessing histamine-related pathologies. Patients with concurrent systemic mastocytosis (SM) and hereditary alpha tryptasemia (HαT) may show increased MC mediator-related symptom severity. We developed and validated a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay to quantify histamine, NMH, and MIMA, and explored their correlation with basal serum tryptase (BST) levels. Methods Using an in-matrix double derivatization, enhancing extraction, we analyzed urinary histamine, NMH, and MIMA with an online solid-phase extraction LC-MS/MS system. Analytical method validation assessed recovery, imprecision, and detection limits. For clinical validation, correlation analysis between BST levels, NMH, and MIMA in SM and HαT patients was performed. Results The assay demonstrated recoveries>98 %, imprecision<3 %, and limits of quantification at 2.0 nmol/L for histamine, 0.53 nmol/L for NMH, and 0.011 μmol/L for MIMA. Patients with a combination of SM and HαT showed a 2.6–3.6 fold increase in BST compared to those with SM alone. A BST/NMH ratio>0.129 predicted HαT with 91.3 % sensitivity and 85.6 % specificity, and a BST/MIMA ratio>7.46 predicted HαT with 89.9 % sensitivity and 86.0 % specificity, independent of SM status. Conclusions Our LC-MS/MS method provides highly accurate and efficient quantification of histamine, NMH, and MIMA. Integrating BST/NMH and BST/MIMA ratios in diagnostic protocols enhances detection of HαT in MC-related disorders, supporting improved diagnostics and tailored patient management.