ImmunoCAP Tryptase measures the level of tryptase released by mast cells into serum. Mast cells play a key role in allergic reactions, and increase in numbers under inflammatory conditions. When activated, they release a variety of mediators that lead to the signs and symptoms of allergic reactions, such as anaphylaxis. These mediators include tryptase and histamine.
A transient increase in the level of tryptase in circulation after a patient suffers an anaphylactic reaction helps to identify and assess the extent of the reaction. A persistent elevated baseline level of tryptase is an indication of possible mastocytosis.
Assessing risk of anaphylactic reactions
Elevated baseline tryptase levels serve as a risk marker for particular patients having severe anaphylactic reactions. Mature tryptase is stored in the granula of resting mast cells. It is released into the bloodstream during mast cell activation, by either IgE- or non-IgE mediated mechanisms. The transiently increased levels of mature tryptase serve as a clinical marker confirming severe reactions as anaphylaxis.
Clinical marker in severe insect venom reaction
The average prevalence of systemic anaphylactic sting reactions is around 3%. Up to 25% of patients with severe venom reactions have an elevated baseline tryptase level. The importance of identifying these patients has been emphasized because they are predisposed to severe anaphylactic reactions. Increased levels may, though not necessarily, be due to an underlying mastocytosis.
Clinical marker in perioperative severe reactions
Elevated baseline tryptase levels indicate an increased mast cell burden, and may serve as a risk factor for severe reactions during surgery. Sensitization (i.e. presence of specific IgE antibodies to substances that patients are exposed to during surgery) is another risk factor. The importance of measuring the transient increase of tryptase during the perioperative phase is well established in confirming an anaphylactic reaction.
Tryptase in mastocytosis and haematological neoplasms
Persistently elevated levels of tryptase proforms in blood reflect the increased abnormal mast cell burden in mastocytosis. These heterogeneous diseases are commonly associated with a mutation in the receptor for the stem cell factor (SCF), a cytokine enhancing the survival and autonomous growth of the mast cells.
The diagnostic and prognostic significance of tryptase is also seen in haematological abnormalities and malignancies (neoplasms) whether systemic mastocytosis is established or not.
Click to view a case study on anaesthetic reactions (pdf)
Tryptase levels (or concentrations) also increase in nasal fluid in:
- Active allergic rhinitis
- Allergen challenge in patients with allergic rhinitis
Expected test values
In healthy individuals, tryptase baseline levels have been reported as approximately 1-15 μg/l. Individuals have their own unique baseline level, which is usually stable over time. Some individuals with elevated baseline levels of tryptase, approximately >10 μg/l, are considered to be at increased risk of severe anaphylactic reaction.
Elevated levels of tryptase can usually be detected for up to 3-6 hours after the anaphylactic reaction. They return to normal within 12-14 hours after release.
Preferably, samples should be collected between 15 minutes and 3 hours after the suspected event causing mast cell activation.
A study with 126 apparently healthy individuals (61 males and 65 females, aged 12-61 years) reported a geometric mean of 3.8 µg/l and a 95th percentile of 11.4 µg/l.
Specimen collection and preparation
Blood should be collected by venipuncture and allowed to clot, and the serum separated by centrifugation. Preferably, samples should be taken between 15 minutes and 3 hours after the event suspected of causing mast cell activation.
Increased levels of tryptase can usually be detected for up to 3-6 hours after the reaction. They return to normal within 12-14 hours after release.
Serum sample storage
Specimens may be kept at room temperature (RT) for shipping purposes for 2 days. Store at 2-8 °C if assayed within 5 days after collection. For longer periods, store samples at -20 °C or -70 °C.
Plasma samples have been assayed and found to give results comparable with those for serum samples.
Diluted and undiluted nasal lavage samples can be used in ImmunoCAP Tryptase. For dilution, use ImmunoCAP IgE/ECP/Tryptase Diluent. Several methods for collecting nasal lavage are described in the literature. Analyze the collected sample in ImmunoCAP Tryptase in accordance with the Directions for Use.
As in all diagnostic testing, a definitive clinical diagnosis should not be based solely on the results of a single test method. A diagnosis should be made by the doctor after the evaluation of all clinical and laboratory findings.
- Hogan AD, Schwartz LB. Markers of mast cell degranulation. Methods 1997; 13: 43-52.
- Rasp G, Hochstrasser K. Tryptase in nasal fluid is a useful marker of allergic rhinitis. Allergy 1993; 48: 72-74.
- Rasp G, Enander I. Mast cell activation in vivo measured by nasal fluid tryptase. XVI Eur Congr Allergology Clin Immunol, ECACI 95.
- Schwartz LB, Bradford TR, Rouse C, Irani A- M, Van der Zwan JK, Van der Linden P-W G. Development of a new, more sensitive immunoassay for human tryptase: use in systematic anaphylaxis. J Allergy Clin Immunol 1994;14(3):190-204.