N-Methyl Histamine (MIAA), Random Urine (Sendout)

General Information

Lab Name

Lab Code

478

External Test Id

NMHR

Description

Useful For:

Screening for and monitoring of mastocytosis and disorders of systemic mast-cell activation, such as anaphylaxis and other forms of severe systemic allergic reactions
Monitoring therapeutic progress in conditions that are associated with secondary, localized, low-grade persistent, mast-cell proliferation and activation such as interstitial cystitis

Patient Preparation:

Patient must not be taking monoamine oxidase inhibitors (MAOIs) or aminoguanidine, as these medications increase N-methylhistamine (NMH) levels.
Patient should avoid consuming histamine-rich food 24 hours prior to/during collection (e.g., cheese, chicken, liver, eggplant, sauerkraut, sirloin steak, spinach, tomatoes, wine, or yogurt).

Ordering Requirements: Pre-approved for UW Medicine Allergy Clinics. Orders from other locations require Laboratory Medicine Resident (LMR) approval.

Ordering Note: This test is for random urine specimens only. For timed collections, refer to N Methylhistamine, 24 Hour Urine (Sendout) [RUNMHT].

Synonyms

1-Methylhistamine, MIAA-Urine, N-methylhistamine, N-Methylimidazoleacetic Acid-Urine, NMHR

Interpretation

Method

N-Methylhistamine: Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Creatinine: Enzymatic Colorimetric Assay

Ref. Range Notes

Reference Ranges:

Age:	N-Methylhistamine Range:
0-5 years	120-510 mcg/g creatinine
6-16 years	70-330 mcg/g creatinine
>16 years	30-200 mcg/g creatinine

Interferences and Limitations

Cautions:

While an average North American diet has no effect on urinary N-methylhistamine (NMH) levels, mild elevations (around 30%) may be observed on very histamine-rich diets. This problem is more pronounced if random-urine specimens are used and collected following a histamine-rich meal.

NMH levels may be depressed in individuals who have an alteration in the histamine-N-methyltransferase gene (HNMT), which encodes the enzyme that catalyzes NMH formation. This alteration results in an amino acid change that decreases the rate of NMH synthesis.

When N-acetylcysteine is administered at levels sufficient to act as an antidote for the treatment of acetaminophen overdose, it may lead to falsely decreased creatinine results.

Ordering & Collection

Specimen Type

Urine

Collection

Within a few hours of symptom onset, collect a random urine specimen in a preservative-free collection container.

Approval Required

Pre-approved for UW Medicine Allergy Clinics. Orders from all other locations require Laboratory Medicine Resident (LMR) approval.

Handling Instructions

Outside Laboratories:

Aliquot 5 mL urine to a plastic screw-cap vial and refrigerate specimen.
Indicate "random collection" on the DLMP requisition.

Stability: Refrigerated (Preferred): 28 days; Frozen: 28 days; Ambient: 14 days.

Quantity

requested: 5 mL urine
minimum: 3 mL urine

Processing

Processing

Aliquot 5 mL urine into a plastic, screw-capped vial and refrigerate.

Login: SEND1-;REFRIG

RSNDT1: MAYO
RSTYP1: URN-RAND
RTSRQ1: ;N Methylhistamine, Random Urine (Mayo Test NMHR)

Sendouts,

Order Mayo Test: NMHR.

Stability: Refrigerated (preferred): 28 days; Frozen: 28 days; Ambient: 14 days.

Performance

LIS Dept Code

Performing Location(s)