Histamine

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At a Glance
Why Get Tested?
To help confirm a diagnosis of anaphylaxis, mastocytosis, or mast cell activation
When To Get Tested?
When you have symptoms such as flushing, nausea, throat swelling or low blood pressure that may be due to a life-threatening allergic reaction; sometimes when your healthcare practitioner suspects that you have mastocytosis or mast cell activation
Sample Required?
A blood sample drawn from a vein in your arm or a 24-hour urine collection
Test Preparation Needed?
None for anaphylaxis, but timing of the sample very soon after the beginning of symptoms is important. If testing is done for other conditions, you may be instructed to refrain from taking antihistamine and other medications. This should be discussed with your health care practitioner.
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The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.
If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.
Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called “normal” values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.
While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are “within normal limits.”
For more information, please read the article Reference Ranges and What They Mean.
What is being tested?
Histamine is a substance that is released from specialized cells called mast cells when they are activated, often as part of an allergic immune response. This test measures the amount of histamine in the blood or urine.
Mast cells are large tissue cells found throughout the body. They are present mainly in the skin, the lining of the intestine and air passages, and the bone marrow. Mast cells are part of the body’s normal response to injury as well as allergic (hypersensitivity) responses. They contain granules that store a number of chemicals, including histamine and tryptase, which are released when mast cells become activated. Histamine is responsible for many of the symptoms in persons with allergies.
Concentrations of histamine in the blood and urine are normally very low. Significant increases can be seen in people with a severe allergic reaction and in those with a disorder in which the number of mast cells increase (proliferate) and/or activate without apparent allergies.
The activation of many mast cells is associated with a severe form of acute allergic reaction termed anaphylaxis, which can cause hives (blisters on the skin), reddening of the skin (flushing), low blood pressure, severe narrowing of the air passages, and even death. With anaphylaxis, histamine concentrations in the blood increase rapidly, rising within 10 minutes of the start of symptoms and returning to normal within about 30 to 60 minutes. This increased production is also reflected a short time later in the urine as histamine and its primary metabolite, N-methylhistamine, are excreted.
Histamine and tryptase levels may be persistently increased in people with mastocytosis. This rare condition is associated with abnormal proliferation of mast cells and their infiltration and accumulation in the skin (cutaneous mastocytosis) and/or in organs throughout the body (systemic mastocytosis).
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm. For a 24-hour urine collection, all of the urine should be saved for a 24-hour period. It is best to keep the sample in a cool, dark place such as a refrigerator.
Is any test preparation needed to ensure the quality of the sample?
If anaphylaxis is suspected, it is important to collect the sample very soon after the beginning of symptoms. If testing is done for other conditions, you may be instructed to refrain from taking antihistamine and other medications. This should be discussed with your health care practitioner.
Common Questions
View Sources
Sources Used in Current Review
Mustafa, S. (2016 May 31, Updated). Anaphylaxis. Medscape Drugs and Diseases. Available online at http://emedicine.medscape.com/article/135065-overview. Accessed on 02/18/17.
Hogan, D. and Mastrodomenico, C. (2016 August 8, Updated). Mastocytosis. Medscape Drugs and Diseases. Available online at http://emedicine.medscape.com/article/1057932-overview. Accessed on 02/18/17.
Henochowicz, S. (2016 March 20, Updated). Anaphylaxis. MedlinePlus Medical Encyclopedia. Available online at https://medlineplus.gov/ency/article/000844.htm. Accessed on 02/18/17.
Onnes, M. et.al. (2016 November 8). Mast Cell Clonal Disorders: Classification, Diagnosis and Management. Curr Treat Options Allergy. 2016; 3(4): 453–464. Available online at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5121168/. Accessed on 02/18/17.
Delgado, J. et. al. (2016 December, Updated). Mast Cell Disorders. ARUP Consult. Available online at https://arupconsult.com/content/mast-cell-disorders Accessed on 02/18/17.
Delgado, J. (2016 August, Updated). Anaphylaxis. ARUP Consult. Available online at https://arupconsult.com/content/anaphylaxis. Accessed on 02/18/17.
Sources Used in Previous Reviews
Mustafa, S. (Updated 2012 February 14). Anaphylaxis. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/135065-overview. Accessed August 2012.
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Mayo Clinic Staff (2010 September 3). Anaphylaxis. MayoClinic.com [On-line information]. Available online at http://www.mayoclinic.com/health/anaphylaxis/DS00009. Accessed August 2012.
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