N Methylhistamine, 24 Hour Urine (Sendout)

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

Patient Preparation:

• Patient must not be taking monoamine oxidase inhibitors (MAOIs) or aminoguanidine, as these medications increase N-methylhistamine (NMH) levels.
• Patient should avoid consuming histamine-rich food 24 hours prior to/during collection (e.g., cheese, chicken, liver, eggplant, sauerkraut, sirloin steak, spinach, tomatoes, wine, or yogurt).

Ordering Requirements: Pre-approved for UW Medicine Allergy Clinics. Orders from other locations require Laboratory Medicine Resident (LMR) approval.

Ordering Note: This test is for timed urine collections only. For random urine collections, refer to N-Methyl Histamine (MIAA), Random Urine (Sendout) [OLTG #478].

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

Creatinine: Enzymatic Colorimetric Assay

Reference Ranges:

24 Hour Collection: Collect urine for 24 hours in a preservative-free amber polyethylene urine collection container. Refrigerate during collection (preferred). Record the collection interval.

• The application of temperature controls (refrigeration) must occur within 4 hours of completion of the collection.
• If the total volume provided is less than 300 mL, the order will be changed to the random urine test by Mayo Clinic.

Outside Laboratories:

• Mix urine well. Measure and record total volume. Document the total volume and collection interval on the DLMP requisition.
• Aliquot 5 mL urine to a plastic screw-cap vial and refrigerate specimen.

Stability: Refrigerated (preferred): 28 days; Frozen: 28 days; Ambient: 14 days.

• The application of temperature controls (refrigeration) must occur within 4 hours of completion of the collection.
• Mix specimen well. Measure and record total volume.
• Document the collection interval and total volume on the requisition. Provide Sendouts with a copy.
• Aliquot 5 mL urine to a plastic, screw-capped vial and refrigerate.

Result-at-entry:

• RUMINT (Collection Interval): <Enter the collection interval in hr.>
• RUMTV (Total Volume): <Enter the total volume in mL.>

Sendouts:

• Order Mayo Test: NMH24.
• Interfaced: Yes.

Stability: Refrigerated (preferred): 28 days; Frozen: 28 days; Ambient: 14 days.