ImmunoCAP Tryptase

Quantifying total tryptase levels with ImmunoCAP Tryptase results in evaluation of risk for severe reactions in venom allergic patients and is also used as one WHO diagnostic criterion for mastocytosis and a marker in haematological neoplasms. Here you can learn more about the clinical value, expected test values and the test principle of ImmunoCAP Tryptase.

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.

Clinical value

Assessing risk for anaphylactic reactions
Elevated baseline tryptase levels serve as a risk marker for certain patients to get severe anaphylactic reactions. Mature tryptase is stored in the granula of resting mast cells. It is released into the bloodstream during mast cell activation, either by 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
In average the 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 as they are predisposed for severe anaphylactic reactions. Increased levels may be, but need 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 which the patients are exposed to during surgery) is another risk factor. To confirm an anaphylactic reaction, the importance of measuring the transient increase of tryptase during the perioperative phase is well established.

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 survival and autonomous growth of the mast cells.

A diagnostic and prognostic significance of tryptase is also seen in haematological abnormalities and malignancies (neoplasms) irrespective if 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 the tryptase baseline levels have been reported to range approximately between 1–15 μg/l. Each individual has its own unique baseline level, which usually is stable over time. Some individuals with elevated baseline levels of tryptase, approximately >10 μg/l, are considered to be at increased risk for severe anaphylactic reaction.

Elevated levels of tryptase can usually be detected for up to 3 to 6 hours after the anaphylactic reaction. They return to normal within 12-14 hours after release.

Samples should preferably 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), showed a geometric mean of 3.8 µg/l and a 95th percentile of 11.4 µg/l.

 

Specimen collection and preparation

Blood collection
Blood should be collected by venipuncture, allowed to clot, and the serum separated by centrifugation. Samples should preferably 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 to 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
Plasma samples have been assayed and found to give comparable results to serum samples.

Nasal lavage
Diluted and undiluted nasal lavage samples can be used in ImmunoCAP Tryptase. For dilution use ImmunoCAP IgE/ECP/Tryptase Diluent. There are several methods for collection of nasal lavage described in the literature. Analyse the collected sample in ImmunoCAP Tryptase according to the Directions for Use.

Important note

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 physician after evaluation of all clinical and laboratory findings.

References

  • 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.

As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.