About the Test
Purpose of the test
Blood levels of tryptase may be measured for several different purposes. For example, testing tryptase may be helpful:
- To determine if a severe allergic reaction, called anaphylaxis or anaphylactic shock, has recently occurred
- To diagnose mast cell disorders, rare conditions in which there are either too many mast cells in the body or the mast cells are abnormally reactive
- To monitor patients with mast cell disorders to see whether their condition is stable or worsening
What does the test measure?
Tryptase is a type of protein, called an enzyme, that is stored in mast cells. Mast cells are white blood cells that are involved in normal immune responses but also become activated during allergic reactions.
Mast cells are found throughout the body. They are most numerous in the places where your body meets external environments and objects such as in your skin and the surfaces of your airway and digestive system. Mast cells in these places can act quickly to guard your body from foreign organisms and toxins.
When mast cells are activated, they rapidly release stored chemicals, including tryptase and histamine. These chemicals cause many of the symptoms associated with allergies like flushing, itching, and difficulty breathing. When people have a severe allergic reaction, blood levels of tryptase typically become elevated very quickly and then return to normal after 12 to 24 hours.
The specific role of tryptase in the body is not completely understood. However, sudden high levels of tryptase in the blood show that mast cells are involved in medical events such as severe allergic reactions. Because of its association with mast cell activation, tryptase serves as a marker of mast cell activity.
When should I get tryptase testing?
The most common reasons for getting tryptase testing are because your doctor seeks to confirm a diagnosis of a severe allergic reaction, called anaphylaxis, or to diagnose or monitor a blood disorder such as a mast cell disorder.
Confirming a diagnosis of anaphylaxis
Tryptase testing may be ordered if a doctor suspects that you have suffered a severe allergic reaction, also called anaphylaxis or anaphylactic shock. Anaphylactic shock is a very serious, potentially fatal condition that comes on rapidly.
Many of the symptoms caused by anaphylaxis may also be associated with other medical emergencies. They can include:
- Difficulty breathing
- Swelling of the face or tongue
- Difficulty swallowing
- Anxiety
- Abdominal pain
- Lightheadedness or dizziness
- Skin reactions, such as redness, itching, or hives
- Chest tightness
- Nausea and vomiting
- Loss of consciousness
Any substance to which a person is allergic can cause anaphylaxis. However, these severe allergic responses are most commonly caused by:
- Drug allergies
- Food allergies
- Insect stings or bites
Severe allergic reactions must be treated very swiftly to prevent life-threatening complications. As a result, the immediate diagnosis of anaphylaxis is usually made based on the patient’s symptoms and medical history. However, because the symptoms of anaphylaxis are similar to other medical emergencies, such as asthma attacks and heart attacks, tryptase testing may be done after treating the allergic reaction in order to confirm the diagnosis.
Testing for high blood levels of tryptase may also be performed during an autopsy to determine if death was caused by a severe allergic reaction.
Diagnosing and monitoring mast cell disorders
Tryptase is found in high concentrations in mast cells, which allows tryptase testing to help diagnose mast cell disorders. Mast cell disorders are uncommon conditions in which patients have too many mast cells in their body or their mast cells are too reactive. These disorders include:
- Systemic mastocytosis (SM): Systemic mastocytosis is a disorder in which abnormal mast cells infiltrate multiple types of tissue such as the skin, bone marrow, and other organs.
- Cutaneous mastocytosis (CM): Cutaneous mastocytosis is a disorder in which clusters of mast cells are present in the skin, which may cause red or brown patches, swelling, itching, or blistering.
- Mast cell activation syndrome This disorder causes recurrent episodes of mast cell activation, leading to allergic symptoms, low blood pressure, flushing, and digestive upset. When this syndrome is caused by a genetic change that results in a mast cell defect, it is called monoclonal mast cell activation syndrome. Sometimes the cause is unknown.
Common signs and symptoms of mast cell disorders that may prompt tryptase testing include:
- Skin symptoms, including flushing, itching, and red or brown patches
- Digestive system symptoms, including heartburn, nausea, and abdominal cramping
- Respiratory and nasal symptoms, including wheezing, nasal congestion, and runny nose
Blood levels of tryptase are tested to diagnose patients who are suspected of having a mast cell disorder. Repeat blood tests of tryptase levels are often performed, and how the patient’s tryptase levels change over time can be considered in making a diagnosis.
People who have been diagnosed with mast cell disorders like mastocytosis are sometimes monitored with tryptase testing. This testing enables doctors to see if their disease is stable or worsening.
Finding a Tryptase Test
How to get tested
Tryptase testing requires a blood sample. In emergency settings, tryptase may be tested soon after the onset of allergic symptoms to detect a severe allergic reaction.
People who are tested immediately following a possible severe allergic reaction are typically tested again approximately 24 hours after allergic symptoms resolve. This second test is done to establish a “baseline,” meaning the normal level of tryptase for the patient. Blood samples given before the allergic reaction, if available, may also be tested to establish a baseline.
If you are being evaluated or monitored for a mast cell disorder or other blood condition, your doctor typically orders a tryptase test, and a blood sample for analysis is drawn in a medical setting.
Can I take the test at home?
At this time, no commercial tests for the tryptase enzyme are available for home use.
How much does the test cost?
The cost of tryptase testing depends on where the test is administered, the laboratory used, whether other tests are performed at the same time, and whether you have medical insurance.
The costs of testing may include an office or hospital visit, a fee for the blood draw, and a laboratory fee for analyzing your blood or plasma sample. These costs are usually covered by insurance when the test is ordered by a doctor. However, you can check with your health care provider to learn if a deductible or copay may be your responsibility.
Taking a Tryptase Test
Tryptase testing requires a small sample of blood. Typically, a blood sample is taken in an emergency room, doctor’s office, lab, or other medical setting.
Before the test
If tryptase testing is ordered to see if you experienced a severe allergic reaction, the doctor ordering the test carefully times the sample collection between 15 minutes to 2-3 hours after signs and symptoms of an allergy began. However, no special preparation is required on your part.
Your health care team may ask you to schedule a blood draw at a time when you don’t have any symptoms of allergy or mast cell activation. This is done to establish your normal, or baseline, tryptase level that can be compared to your tryptase level that was measured when you had symptoms.
During the test
During a tryptase test, a health care provider will extract a small sample of blood. In a hospital setting, a blood sample may be taken from an intravenous catheter, if available.
A blood sample may also be taken from a vein in your arm. For this type of blood draw, an elastic band is tied around your upper arm to increase blood in the veins and make them easier to identify. The puncture site is wiped with an antiseptic. A small sample of blood is then withdrawn using a needle attached to a collection tube.
You may feel a brief sting when the needle pierces your skin. It usually takes less than a minute to obtain a blood sample.
After the test
A bandage or cotton swab is used to prevent further bleeding after your blood sample has been taken. This usually needs to be kept in place for about an hour.
As long as you are otherwise feeling well, you may return to your normal activities, including driving, after the test. If you notice any lasting pain, bleeding, or signs of infection at the site where the blood was drawn, you should contact your doctor.
Tryptase Test Results
Receiving test results
Tryptase testing on a blood sample takes several hours, so test results are not immediately available after a blood draw.
If your blood level of tryptase was performed to confirm a severe allergic reaction, a second test will be performed after symptoms resolve to establish a baseline. The baseline reveals what your body’s normal blood level of tryptase is.
Tryptase test results are generally available within one or two business days. Your doctor may call or schedule an appointment to discuss the results with you, or you may access the results through an online portal.
Interpreting test results
On average, most people have a blood level of tryptase from 3 to 5 nanograms per milliliter (ng/mL). For medical tryptase testing, the American Board of Internal Medicine considers a level under 11.5 ng/mL to be within the normal range.
In many medical situations, a second tryptase level is obtained to compare to an abnormal initial test. A test that is obtained after symptoms have disappeared is called a baseline test.
Determining your baseline allows the doctor to most appropriately interpret tryptase test results in your specific situation. For example, even a tryptase level below the normal limit of 11.5 ng/mL may cause concern if it represents a significant rise above your baseline level. The doctor who ordered your tryptase test can tell you the meaning of your different tryptase levels.
Comparing a test result from a time when symptoms were present to a repeat or baseline test can assist in narrowing down a potential diagnosis. The table below provides examples of how initial and repeat tryptase tests may be interpreted:
| Test Result When Symptoms Are Present | Repeat Test/Baseline Test | Possible Diagnoses |
|---|---|---|
| High | Normal | Anaphylactic shock or mast cell activation syndrome |
| High | High | Systemic mastocytosis, certain genetic syndromes, or some blood or kidney disorders |
| Normal | Normal | Mastocytosis affecting the skin only, or another condition that does not involve mast cell activation |
Persistent high tryptase levels in the blood may also be detected in other diseases, including leukemia, chronic kidney failure, chronic liver failure, and other rare blood diseases.
When tryptase is measured as a way of monitoring systemic mastocytosis, stable tryptase levels over time suggest a favorable outcome, while rising levels can mean the disease may be more likely to get worse.
Elevated tryptase and hereditary alpha tryptasemia
High levels of tryptase in the blood may also be due to an inherited condition called hereditary alpha tryptasemia, which causes elevated baseline tryptase levels.
It is estimated that up to 6 percent of the population has hereditary alpha tryptasemia, and it is believed to be the most common reason for higher than normal baseline tryptase.
Hereditary alpha tryptasemia is inherited, meaning affected people have a genetic change that was passed down to them from one of their parents. Specifically, people with hereditary alpha tryptasemia have extra copies of the TPSAB1 gene.
Sometimes people with hereditary alpha tryptasemia do not have any symptoms. In other cases, they may have allergic, gastrointestinal, cardiac, and other symptoms similar to those experienced by people with mast cell activation disorders.
Although tryptase testing is not usually done specifically to look for hereditary alpha tryptasemia, knowledge of this condition may influence how a doctor interprets high tryptase levels found on a blood test.
Are test results accurate?
Tryptase test results are generally regarded as accurate, although there are potential sources of error in the processing and analysis of any blood sample.
When tryptase is used to determine whether a severe allergic reaction occurred, the timing of obtaining a blood sample is crucial. Tryptase typically peaks 30 minutes to 2 hours after the onset of an allergic episode and then declines rapidly. If the blood sample is drawn too early or late, results may be misleading.
Do I need follow-up tests?
Whether follow-up testing is necessary depends on the reason for tryptase testing and the test result.
Patients whose tryptase test results indicate a severe allergic reaction will often have additional testing to determine the substance that triggered the reaction.
Patients being evaluated for mast cell disorders will have their tryptase level repeated if it is found to be abnormally high. Additional tests to evaluate for other abnormalities and problems with vital organs caused by mast cells may include:
- Skin biopsy
- Complete blood count (CBC) with differential
- Liver function tests
- Testing for genetic mutations
- Bone marrow biopsy
Questions for your doctor about test results
After your tryptase test results are available, it may be helpful to ask your doctor some of the following questions.
- Were my tryptase test results normal?
- Were you able to determine my normal, or baseline, level of tryptase?
- Do my tryptase test results indicate that I had a severe allergic reaction?
- If I had an allergic reaction, will additional tests be needed to determine what I’m allergic to?
- Do my tryptase test results show that I may have a mast cell disorder?
- Do you recommend any follow-up tests related to my tryptase test result?
Comparing and contrasting tryptase testing and allergy blood testing
The purpose of tryptase testing when a severe allergic reaction may have occurred is to confirm that the patient’s symptoms were caused by an allergy. A test result which shows high levels of tryptase can confirm that an allergic reaction occurred, but it does not tell the doctor what specific substance triggered the allergic reaction.
Allergy blood testing is also used to determine if a person suffers from allergies. A particular type of allergy blood testing, called specific IgE testing, is used to determine what substance or substances cause a person’s allergy symptoms. Allergy blood testing may also be performed to see if a child has outgrown an allergy.
Often, an elevated tryptase level after a severe allergic reaction will prompt allergy blood testing to determine what may have provoked the severe reaction.
