N-Methylhistamine, 24 Hour Urine

Message

For Specimen Integrity during Extreme Weather see the “Lockbox Usage in Extreme Weather” document at the top of this page.

Test Code

NMHIN

Alias/See Also

1-Methylhistamine
Histamine Metabolites
Urinary N-Methylhistamine

CPT Codes
82542

Includes

N-Methylhistamine,
24 Hr, U;
Creatinine, 24 HR, U

Preferred Specimen

5 mL Aliquot of 24 hour Urine

Patient Preparation
Patient Preparation: Patient must not be taking monoamine oxidase inhibitors (MAOIs) or aminoguanidine as these medications increase N-methylhistamine (NMH) levels.

Minimum Volume

3 mL

Instructions

Collection Instructions:
1. Collect urine for 24 hours.
2. No preservative.
3. Aliquot into plastic tube and send at refrigerate temperature.
If ordering this test with 23BPT / 2,3-Dinor 11 Beta-Prostaglandin F2 Alpha, 24 Hour, Urine, both tests must be ordered under different order number. They cannot share an order number.

Transport Container

pour off Tube

Transport Temperature

Refrigerated

Specimen Stability

Room Temperature: 14 days
Refrigerated: 28 days
Frozen: 28 days

Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)

All specimens will be evaluated at Mayo Clinic Laboratories for test suitability.

Methodology
Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) and Enzymatic Colorimetric Assay

Setup Schedule

Tuesday, Thursday

Report Available

3 - 7 days

Limitations

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.

Clinical Significance

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 24-hour urine collection specimens Monitoring therapeutic progress in conditions that are associated with secondary, localized, low-grade persistent, mast-cell proliferation and activation such as interstitial cystitis

Performing Laboratory
Mayo Clinic Laboratories
200 First Street SW
Rochester, MN 55905

Last Updated: November 22, 2021

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.