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Test ID NMH24 N-Methylhistamine, 24 Hour, Urine

Ordering Guidance

Random urine collections are preferred for patients with episodic symptoms, for example in the context of allergic reactions, brought on by specific environmental factors; order NMHR / N-Methylhistamine, Random, Urine.


If the total volume provided is less than 300 mL, this test will be canceled and NMHR ordered and performed.

Necessary Information

Specimen volume and duration are required.

Specimen Required

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

Supplies: Sarstedt 5 mL Aliquot Tube (T914)

Container/Tube: Plastic, 5-mL tube

Specimen Volume: 5 mL

Collection Instructions:

1. Collect urine for 24 hours.

2. No preservative.

3. Aliquot into plastic tube and send at refrigerate temperature.

Additional Information: See Urine Preservatives-Collection and Transportation for 24-Hour Urine Specimens for multiple collections.

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 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

Profile Information

Test ID Reporting Name Available Separately Always Performed
NMH1D N-Methylhistamine, 24 Hr, U No Yes
CRT24 Creatinine, 24 HR, U No Yes

Method Name

NMH1D: Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

CRT24: Enzymatic Colorimetric Assay

Reporting Name

N-Methylhistamine, 24 Hr, U

Specimen Type


Specimen Minimum Volume

3 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Urine Refrigerated (preferred) 28 days
  Frozen  28 days
  Ambient  14 days

Reference Values


0-5 years: 120-510 mcg/g creatinine

6-16 years: 70-330 mcg/g creatinine

>16 years: 30-200 mcg/g creatinine



Males: 930-2955 mg/24 hours

Females: 603-1783 mg/24 hours


Reference values have not been established for patients who are younger than 18 years of age.


For SI unit Reference Values, see

Day(s) Performed

Tuesday, Thursday

Report Available

3 to 7 days

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Test Classification

This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
NMH24 N-Methylhistamine, 24 Hr, U 44340-8


Result ID Test Result Name Result LOINC Value
CR_A Creatinine, 24 HR, U 2162-6
605159 N-Methylhistamine, 24 Hr 44340-8
TM10 Collection Duration 13362-9
VL8 Urine Volume 3167-4
CR_24 Creatinine Concentration, 24 HR, U 20624-3

Urine Preservative Collection Options

Note: The addition of preservative or application of temperature controls must occur within 4 hours of completion of the collection.







50% Acetic Acid


Boric Acid


Diazolidinyl Urea


6M Hydrochloric Acid


6M Nitric Acid


Sodium Carbonate