Systemic mastocytosis (SM) is a disorder characterized by the abnormal accumulation of mast cells, which are typically responsible for allergic reactions. Mast cells are trigged by unique antigens, which means that each individual responds in a different way when mast cells are activated in the body. For example, individuals may be allergic to cats but not ragweed, and they may experience watery eyes and a runny nose or hives or asthma in response to their specific allergies.
An abnormal accumulation of mast cells will not necessarily cause any symptoms, unless they are triggered, at which point, the cells release an excess amount of allergic signal. Depending on which tissue the mast cells are accumulating and the manner in which they respond, the symptoms could range from hot flashes, itching, syncope, diarrhea, tachycardia, gastrointestinal distress, or even loss of consciousness.
Because of its intermittent nature of symptoms and the variety of symptoms possible, SM is difficult to diagnose. The World Health Organization recommends a bone marrow biopsy, specialized cytology studies, or genetic testing to diagnose SM. However, urine concentrations of N-methyl histamine (NMH) and 11-beta prostaglandin F2α (BPG), which are metabolites of mast-cell-derived histamine and prostaglandin, have also been used to aid in screening and the reduction of unnecessary biopsies. Cysteinyl leukotrienes are another class of mast cell secretory molecules and potent inflammatory mediators. Leukotriene E4 (LTE4) is the primary stable metabolite of total cysteinyl leukotrienes.
Mayo Clinic researchers hypothesized that urinary LTE4 could be used alone or in combination with NMH and BPG to optimize screening for SM. In a recent study published in Clinical Biochemistry, the researchers describe a novel (LC–MS/MS) assay to accurately and precisely quantitate LTE4 in urine and outline its clinical utility in SM screening.
“We began this study when Mayo Clinic allergists approached us with a request for a biomarker in the arachidonic acid pathway for use in SM screening. Since SM symptoms are intermittent and often non-specific, clinicians were looking for a biomarker to aid in screening prior to the painful and expensive diagnostic workup,” said Jeff Meeusen, Ph.D., a Consultant in the Cardiovascular Laboratory Medicine Group at Mayo Clinic and author on the paper.
In determining the study method, an ELISA method was initially evaluated, however LC–MS/MS was ultimately decided upon.
“In using an ELISA method, we were concerned about analytical specificity, since there are a variety of naturally occurring compounds with similar structure to LTE4. We chose instead to use LC–MS/MS due to its increased selectivity, and we had experience with tests that measure similar molecules,” said Dr. Meeusen.
Since leukotrienes are one of the chemicals released by mast cells when triggered, basic science research suggested that most leukotrienes are eventually converted to LTE4. In collaboration with Mayo Clinic allergists, the research team recruited 400 patients with symptoms that might be consistent with SM and collected urine samples. Patients went on to be diagnosed (or not) by the conventional means. Researchers measured LTE4 in the collected samples and compared them with the clinical diagnoses.
The results demonstrated that LTE4 can be accurately and reproducibly measured in urine by LC–MS/MS. In patients presenting with suspected SM, elevated urine LTE4 was 48% sensitive and 84% specific for SM. Combining the results of LTE4 with other mast cell biomarkers N‑methyl histamine and 11BPG provided a negative predictive value of 99%.
“We have developed a high-throughput LC–MS/MS method to measure urinary LTE4 with suitable accuracy, precision, and stability for clinical applications,” said Dr. Meeusen.
For more information about the Leukotriene E4, Urine test, visit MayoMedicalLaboratories.com.
By April Josselyn