N-Methylhistamine, Random, Urine

Casandra

Casandra Test Code MC74082Version 1 (DRAFT)

Performing Lab

Lab Mayo Clinic LabLab Test ID NMHR1CPT Codes 82542, 82570

N-Methylhistamine, Random, Urine

Clinical Use

Use

Screening for and monitoring of mastocytosis and disorders of systemic mast-cell activation, such as anaphylaxis and other forms of severe systemic allergic reactions using random urine specimens. Monitoring therapeutic progress in conditions that are associated with secondary, localized, low-grade persistent mast‑cell proliferation and activation such as interstitial cystitis. Increased concentrations of urinary N‑methylhistamine (NMH) are consistent with urticaria pigmentosa (UP), systemic mastocytosis, or mast‑cell activation. Urinary NMH measurements have superior sensitivity and specificity than histamine. Up to 25% variability may be observed in random‑urine excreted levels, making 24‑hour urine collections preferable for borderline results. Children have higher NMH levels than adults; by age 16, adult levels are reached. Reference intervals: 0‑5 years: 120‑510 mcg/g creatinine; 6‑16 years: 70‑330 mcg/g creatinine; >16 years: 30‑200 mcg/g creatinine. (Mayo Clinic Laboratories)

Special Instructions

Not provided.

Limitations

Not all patients with systemic mastocytosis or anaphylaxis will exhibit concentrations outside the reference range; healthy individuals may occasionally exhibit values just above the upper limit of normal. There is significant overlap in values between UP and systemic mastocytosis; NMH measurements should not be relied upon alone. Up to 25% variability in random‑urine excreted levels may be observed. Mild elevations (around 30%) may occur on histamine‑rich diets, especially with random‑urine specimens. NMH levels may be depressed in individuals with alterations in the histamine‑N‑methyltransferase gene (HNMT). N‑acetylcysteine may lead to falsely decreased creatinine results.

Test Details

New York Approved