Patient must not be taking monoamine oxidase inhibitors (MAOIs) or aminoguanidine as these medications increase N-methylhistamine (NMH) levels
Application of temperature controls must occur within 4 hours of completion of the collection.
Refrigerated (preferred) - 28 days
Frozen - 28 days
Ambient - 28 days
NMH1D: Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)
CRT24: Enzymatic Colorimetric Assay
0 - 5 years: 120 - 510 µg/g creatinine
6 - 16 years: 70 - 330 µg/g creatinine
> 16 years: 30 - 200 µg/g creatinine
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-methyl transferase gene, 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.