ImmunoCAP Tryptase

Quantifying total tryptase levels with ImmunoCAP Tryptase results in evaluation of risk for severe allergic reaction

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.

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

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.

Test principle

The technology is based on an extremely high total binding capacity, achieved through a high binding capacity per mg cellulose in combination with an optimal amount of cellulose in each solid phase. This ensures binding of all relevant antibodies, regardless of antibody affinity, still giving low non-specific binding.

The ImmunoCAP solid phase consists of a cellulose derivative enclosed in a capsule. The hydrophilic, highly branched polymer provides an ideal microenvironment for allergens, binding them irreversibly while maintaining their native structure.

The test is designed as a sandwich immunoassay. 

Anti-tryptase, covalently coupled to the solid phase, reacts with the tryptase in the patient serum sample.
After washing, enzyme-labelled antibodies against tryptase are added to form a complex.
After incubation, unbound enzyme-anti-tryptase is washed away, and the bound complex is then incubated with a developing agent.
After stopping the reaction, the fluorescence of the eluate is measured. The fluorescence is directly proportional to the concentration of tryptase in the serum sample.

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.