When you have symptoms such as flushing, nausea, throat swelling, or low blood pressure that may be due to a life-threatening allergic reaction; when your healthcare professional suspects that you have mastocytosis or mast cell activation syndrome.
A blood sample taken from a vein in your arm
None, but timing of the sample soon after the beginning of symptoms can be important.
Tryptase is an enzyme that is released, along with histamine and other chemicals, from mast cells when they are activated as part of a normal immune response as well as in allergic (hypersensitivity) responses. This test measures the amount of tryptase in the blood.
Mast cells are immune cells resident in tissues throughout the body. They are present in highest amounts in the skin, the lining of the intestine and air passages, and the bone marrow. They contain granules that store a number of chemicals, including tryptase and histamine. When mast cells are activated, they release their contents. If a person has clumps of abnormal mast cells (mastocytosis) and/or the cells are activated inappropriately, the chemicals that are released (especially histamine) may cause symptoms that range from moderate to life-threatening.
Normally, the level of tryptase in the blood is very low. When mast cells are activated, the level increases rapidly, rising within 15 to 30 minutes, peaking at 1 to 2 hours, and returning to normal after several hours to a couple of days. In people with severe allergies, activation of many mast cells can cause an extreme form of allergic reaction known as anaphylaxis, which can cause low blood pressure, hives (nettle rash or blisters on the skin), severe narrowing of the air passages, and even death. Tryptase levels will be very high in people with anaphylaxis.
In some cases, tryptase levels will be high in persons with mast cell activation disorders, in which mast cells become activated without apparent allergies or other reasons.
Tryptase levels can also be significantly and persistently increased with mastocytosis, a rare group of disorders associated with an abnormal increase in the number of mast cells. These cells may accumulate in the skin (cutaneous mastocytosis) or in organs throughout the body (systemic mastocytosis).
While cutaneous mastocytosis typically only causes skin problems (particularly hives), people with systemic mastocytosis may experience anaphylaxis and its associated symptoms and are at especially high risk of anaphylaxis with venoms (e.g. Bee or Wasp). These symptoms may be persistent and are related to the organs affected by mast cell accumulation. Systemic mastocytosis may progress slowly or may be aggressive, causing organ dysfunction and, in rare cases, causing a form of leukaemia.
How is it used?
The tryptase test is a useful indicator of mast cell activation and number. Mast cells are immune cells present in highest amounts in the skin, the lining of the intestine and air passages, and the bone marrow. They release tryptase and other substances as part of the body's normal response to injury or parasite infection but also may release them as part of an allergic response. The tryptase test may be used:
- To confirm a diagnosis of anaphylaxis. Anaphylaxis is primarily diagnosed clinically, but a total tryptase should be requested, to help confirm anaphylaxis as the cause of someone's acute symptoms. This is especially true if the person has recurrent episodes and/or if the diagnosis is uncertain.
- To help diagnose mastocytosis (too many mast cells) or a mast cell activation disorder. Mastocytosis is a rare group of disorders associated with an abnormal increase in the number of mast cells, which may accumulate in the skin (cutaneous mastocytosis) or in organs throughout the body (systemic mastocytosis).
Other tests may be used to evaluate a person's health status and to help rule out other conditions that can cause similar symptoms. These may include:
- Allergen-specific IgE blood tests to help determine the cause of an allergic reaction
- Full Blood Count (FBC) to evaluate red and white blood cells
- Renal, liver and thyroid function tests, plus bone profile to evaluate organ function
- 5-hydroxyindoleacetic acid (5-HIAA) urine test to rule out a carcinoid tumour that may cause similar symptoms, such as flushing, diarrhoea, and/or wheezing
- Gastrin test to look for increased secretion of this hormone, which may cause stomach or intestinal ulcers
Occasionally, a tryptase test may be performed postmortem to help determine if anaphylaxis was the cause of a person's death.
When is it requested?
Tryptase is not a frequently requested test. The NICE guidelines for the management of suspected anaphylaxis state that a tryptase series of blood tests should be sent to the laboratory for testing in all cases . Mastocytosis is rare. Symptoms of anaphylaxis may include:
- Swelling of the throat, face, tongue, and/or eyes
- Low blood pressure
- Nausea, vomiting, diarrhoea, abdominal pain
- Cardiac arrhythmias
- Light-headedness or dizziness
- Difficulty breathing, wheezing
- Itching, often with visible hives
- Confusion and/or loss of consciousness
Many of these symptoms are also seen with other conditions.
This test may also be requested when a healthcare professional suspects that a person may have cutaneous or systemic mastocytosis or a mast cell activation disorder. People with such conditions may have many of the same symptoms and signs as people with severe allergies but often without any specific trigger, such as exposure to a specific food (such as peanuts) or a bee sting. People with systemic mastocytosis may have symptoms that indicate organ involvement, such as peptic ulcers, chronic diarrhoea, and joint pain. There may be enlargement of organs such as the liver, spleen, or lymph nodes. There may be skin involvement with rashes or characteristic red, blistering lesions.
A tryptase test may be requested after a person's death to help determine if anaphylaxis was the cause of death.
What does the test result mean?
Normal tryptase results may indicate that a person's symptoms are not due to mast cell activation, or there could be a problem with sample timing. With anaphylaxis, tryptase concentrations typically peak about 1 to 2 hours after symptoms begin. If a sample is drawn too early or late, results may be normal. If a histamine test is also performed, it can be compared to the tryptase levels. Histamine concentrations peak within several minutes of the onset of anaphylaxis and fall within about an hour. If the timing of sample collection was appropriate and neither the histamine or tryptase concentrations are elevated, it is unlikely that a person had anaphylaxis, but it cannot be ruled out.
Acutely elevated tryptase concentrations in a person with symptoms of anaphylaxis indicate it as the likely diagnosis. A baseline sample for comparison is always required.
Persistently elevated tryptase concentrations in a person with symptoms of mast cell activation suggest that the person may have mastocytosis. Additional testing is required to confirm this diagnosis. Tryptase concentrations are thought to correlate with mast cell "burden" (quantity) in those with systemic mastocytosis.
Is there anything else I should know?
If systemic mastocytosis is suspected, an elevated tryptase test result may be followed by a bone marrow aspiration and biopsy to determine if systemic mastocytosis is present. Typically, there are clusters of increased numbers of mast cells in the bone marrow in this disease.
The release of tryptase from mast cells may be triggered by a wide variety of substances, but reaction to a food is thought to be the most common cause of anaphylaxis.
Anyone can have mastocytosis, but children are more frequently affected with cutaneous mastocytosis. In children, mastocytosis is more likely to be self-limited and may be transient.
Studies have linked genetic mutations with some cases of systemic mastocytosis. One of the common mutations identified is a codon-816 C-KIT mutation (CD117). Testing for this mutation is not routine but may occasionally be performed.
Can tryptase testing be done in my doctor's surgery?
If I think I have an allergy, should I have a tryptase test done?
How is anaphylaxis treated?
Anaphylaxis can be rapidly fatal and requires immediate medical treatment with injections of epinephrine and other medications. This is followed by careful monitoring as it is not uncommon for anaphylaxis to recur within hours or days of the initial episode. Those who are known to have severe allergic reactions are encouraged to carry a kit that contains an emergency injection of epinephrine with them at all times.
If I have an elevated tryptase, does this mean I have mastocytosis?
Not necessarily. Tryptase is just one of the criteria that your healthcare professional will consider before making a diagnosis of mastocytosis, which is a rare disorder. Patients who are rheumatoid factor positive can have a falsely elevated tryptase result. Not all tests are affected by this, so discuss with your healthcare professional.