Test Name: N-METHYLHISTAMINE, 24-HOUR URINE
Test Code: 2193875
Alias: LAB11639
NMH24
CPT Code(s): 82542  
Test Includes:

N-Methylhistamine, 24 Hour, Urine 

Creatinine, 24 Hour, Urine   

Preferred Specimen:

5mL aliquot of a well-mixed 24 hour urine
Container:

Clear urine aliquot
Alternate Container: Sterile container
Collection Instructions:

1. Collect urine for 24 hours.

 

2. No preservative.

3. Document total volume.

 

4. Aliquot into plastic tube and send refrigerated.
Transport Temperature:

Refrigerated
Stability:

Room Temp: 14 days

Refrigerated (preferred): 28 days    

Frozen: 28 days
Rejection Criteria:

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

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

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

Set Up: Monday, Wednesday, Friday

TAT: 4-8 days
Method:

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

CRT24: Enzymatic Colorimetric Assay
Performing Lab: Mayo Clinic Laboratories #NMH24
Clinical Significance:

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.
Use: Updated: 02/27/2026
Reference Ranges:

N-METHYLHISTAMINE:

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

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

>16 years: 30-200 mcg/g creatinine

CREATININE:

Males: 930-2955 mg/24 hours

Females: 603-1783 mg/24 hours

 

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

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The CPT codes included in this publication are in accordance with Current Procedural Terminology, a publication of the American Medical Association. CPT codes are provided here for the convenience of our clients; however, correct coding often varies from one carrier to another, and HealthLab may bill specific carriers using codes other than those shown. Clients who bill for services should verify the code(s) with the applicable payor to confirm that their use is appropriate in each case.
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