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While the anaphylactic and systemic symptoms experienced by patients with mast cell disorders are initial indicators of the condition, Mast Cell Tryptase (MCT) is the most affirmative way to make a diagnosis.1 Tryptase measurement should be considered, together with a thorough case history and relevant specific IgE antibody testing, as a diagnostic tool in suspected mast cell activation.
It can also aid in the diagnosis of anaphylaxis. The World Health Organization (WHO) has a consensus on definitions of various forms of mastocytosis and on diagnostic criteria.1
| A. Major criteria |
| 1. Histological/immunohistochemical alterations: mast cell aggregates containing more than 15 mast cells in bone marrow sections |
| B. Minor criteria |
| 1. Cytological alterations: >25% of morphologically abnormal mast cells 2. Detection of c-kit mutations on codon 816 3. Immunophenotypic alterations: expression of CD25 (± CD2) in mast cells from bone marrow, peripheral blood or other organs 4. Total serum tryptase levels persistently >20ng/mL (not applicable if there is a related blood disorder or evidence of acute mast cell release) |
| C. Diagnosis of systemic mastocytosis |
a. at least 1 major criterion + 1 minor criterion b. at least 3 minor criterion |
This robustness of tryptase makes it a useful tool for confirming mast cell involvement in severe reactions like anaphylaxis. Because the individual serum baseline tryptase level is stable over time, you can easily make comparisons between peak and baseline values.1-4 Together with clinical findings, tryptase test results can help you rule in systemic mastocytosis and help you follow your patient’s disease.
Patients with suspected mastocytosis, who may also have had an anaphylactic reaction, or who are being considered for venom-specific immunotherapy (VIT) after previous reactions to bee and/or wasp stings can benefit from tryptase measurement as tryptase baseline levels reflect the mast cell burden in the body. Together with clinical findings, ImmunoCAPTM Tryptase results can help to:
Rule in systemic mastocytosis
Follow up mastocytosis development
A tryptase test is often used as an initial test for mast cell activation. A persistently elevated baseline level of tryptase above 20 μg/l is an indication of possible mast cell disorders and is recognized by the WHO as one minor diagnostic criterion of systemic mastocytosis.1
ImmunoCAP Tryptase measures the total level of tryptase released by mast cells into the circulation. This enables the measurement of transient increases in the level of tryptase after an anaphylactic reaction, as well as establishment of the person’s baseline tryptase level. ImmunoCAP Tryptase measures both alfa- and beta forms of tryptase.
Collecting a sample
The measuring range is 1–200 μg/l and the amount of serum or plasma needed per test is 40 μl. Both serum and plasma samples from venous blood can be used. There is no need for special procedures when collecting blood or preparing the samples.
Sample 1 (peak level): as soon as possible after the reaction (15 minutes to 3 hours).4-6
Sample 2 (baseline level): after complete resolution of all clinical symptoms (approx. 24 to 48 hours, or later).7-10
Timing
Tryptase levels peak between 15 and 120 minutes after an anaphylactic reaction. Usually the elevated levels of tryptase can be detected for up to 3 to 6 hours after the anaphylactic reaction, and it returns to baseline normal level within 12-14 hours. If levels are still above normal range after 24 hours, another sample should be taken after 1-2 weeks to establish baseline levels. Sequential measurement during anaphylaxis and comparison to individual baseline levels has also been suggested.
To measure baseline level:
Blood samples can be collected any time (before or after) outside the period of an acute reaction.7-10
To confirm mast cell activation:
Blood samples should be collected as close to the reaction as possible, between 15 minutes and 3 hours after the onset of anaphylactic symptoms. Elevated tryptase levels can usually be detected up to 6 hours following an anaphylactic reaction and return to baseline levels approximately 24–48 hours after complete resolution of all clinical symptoms.4-6
Mast cell activation is confirmed if: ∆-tryptase (peak – baseline) is ≥ 20 % of the individual’s own baseline tryptase + 2 μg/l.11
Tryptase is an enzyme and is the most abundant protein in mast cells. Within the mast cell mature tryptase is stored in granules as a heparin-stabilized active tetramer.
Proforms of α-tryptase and ß-tryptase are continuously released into the circulation and constitute the individual baseline tryptase level in serum or plasma. Each individual has his/her own unique baseline level of total tryptase which is normally stable over time.2,6,12
Measurement of mast cell tryptase concentrations is used to distinguish mast cell-dependent reactions such as anaphylactic reactions from other systemic disturbances which may present with similar clinical manifestations.
A tryptase test can also help:
Confirm mast cell activation in anaphylaxis
Rule in systemic mastocytosis
Guide VIT treatment
Follow-up development of mastocytosis
If a person's baseline tryptase level is not raised and the dermatology specialist after the clinical evaluation makes the diagnosis of cutaneous mastocytosis (CM), the patient needs to be followed up regularly since the CM may develop into more severe systemic and aggressive forms.1,13,14
