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N-Methylhistamine, 24 Hour Urine
Test CodeLAB01223
Alias/See Also
LAB01223
Mayo TC: NMH24
Mayo TC: NMH24
CPT Codes
82542
Includes
N-Methylhistamin, 24 Hour
Creatinine, 24 Hour
Creatinine, 24 Hour
Preferred Specimen
5mL of a 24 Hour Urine Collection - Recored total volume and duration of collection.
No Preservatives.
No Preservatives.
Patient Preparation
24 hours urine collection is required. If the total volume provided is less than 300 mL, this test will be cancelled.
Minimum Volume
3mL of a 24 Hour Urine Collection.
Transport Temperature
Refrigerated
Specimen Stability
Refrigerated: 28 days
Methodology
N-Methylhistamine - LC-MS/MS
Creatinine - Enzymatic Colorimetric Assay
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. 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.
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.
Reference Range
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
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
Clinical Significance
Increased concentrations of urinary N-methylhistamine (NMH) are consistent with urticaria pigmentosa (UP), systemic mastocytosis, or mast-cell activation. Because of its longer half-life, urinary NMH measurements have superior sensitivity and specificity than histamine, the parent compound. However, not all patients with systemic mastocytosis or anaphylaxis will exhibit concentrations outside the reference range and healthy individuals may occasionally exhibit values just above the upper limit of normal.
The extent of the observed increase in urinary NMH excreation is correlated with the magnitude of mast-cell proliferation and activation, UP patients, or patients with other localized mast-cell proliferation and activation, show usually only mild elevations, while systemic mastocytosis and anaphylaxis tend to be associated with more significant rises in NMH excretion (2-fold or more). There is, however, significant overlap in values between UP and systemic mastocytosis, and urinary NMH measurements should not be relied upon alone in distinguishing localized from systemic disease.
Children have higher NMH levels than adults. By the age of 16, adult levels have been reached.
The extent of the observed increase in urinary NMH excreation is correlated with the magnitude of mast-cell proliferation and activation, UP patients, or patients with other localized mast-cell proliferation and activation, show usually only mild elevations, while systemic mastocytosis and anaphylaxis tend to be associated with more significant rises in NMH excretion (2-fold or more). There is, however, significant overlap in values between UP and systemic mastocytosis, and urinary NMH measurements should not be relied upon alone in distinguishing localized from systemic disease.
Children have higher NMH levels than adults. By the age of 16, adult levels have been reached.
Performing Laboratory
Mayo Clinic Laboratories