Serum Tryptase
No Results
No Results
processing….
The reference range is < 11.4 ng/mL.
There is only one commercially available method for measuring human serum tryptase levels (ImmunoCap Tryptase, Phadia Laboratory Systems, Uppsala, Sweden). According to a study cited by the manufacturers, the 95th percentile value for serum tryptase measured in 126 healthy individuals aged 12-61 years, was 11.4 ng/mL. The geometric mean is 3.8 ng/mL and the lower limit of detection is 1 ng/mL. [1]
The reference values for children aged 6 months to 18 years appear to be similar to adult values with a median range of 3.5 ng/mL as determined by a study on 197 children. [2] Infants younger than 6 months, however, have a higher median value of 6.1 ng/mL. [3]
Tryptase levels of 11.5 ng/mL or greater are indicative of either mast cell activation (as in anaphylaxis) or increased total mast cell levels (as in mastocytosis). The assay does not distinguish between α or β tryptase (both inactive monomeric and active tetrameric form). As such, determinations of tryptase levels are contingent on both the size and activation status of an individual’s mast cell population but is not informative of the specific contribution of either of these factors. [4]
False-positive results may arise from the presence of heterophilic antibodies in the patient’s serum. Heterophilic antibodies, such as rheumatoid factor (RF) and human anti-mouse antibodies (HAMA), can bind to immune globulins of other species and thus interfere with the immunoassay since the tryptase immunoassay employs mouse-derived anti-tryptase. The presence of these heterophilic antibodies can thus lead to spurious elevations, especially in individuals who have received chimeric antibodies (such as Infliximab). [5] Most laboratories that use the serum tryptase immunoassay use a reagent with a suppressor for these heterophilic antibodies.
False-negative results typically result from sample collection later than 12 hours following onset of symptoms.
The currently available serum tryptase assay (ImmunoCap Tryptase, Phadia Laboratory Systems, Uppsala, Sweden) uses quantitative fluorescence to determine serum tryptase levels. [1] The assay does not distinguish between α or β tryptase (both inactive monomeric and active tetrameric form).
Venipuncture is used for specimen collection, and a red-top tube (preferable) or a serum gel separator tube is used. If anaphylaxis is suspected, sample collection should take place 15 minutes to 3 hours after onset of allergic signs and symptoms. Elevated levels can be detected 3-6 hours after the reaction and normalize in 12-14 hours. [6]
The serum or plasma (results are compatible with each other) is then separated with centrifugation or via clotting in a gel separator tube. At least 0.2-0.5 mL of serum is required, meaning that at least 0.5-1 mL of blood needs to be collected. Mild hemolysis, lipemia, and icterus in the sample are acceptable.
If blood collection is not possible, nasal lavage/wash sample is an alternative. [7] In this case, the sample needs to be diluted with the diluents included in the testing kit.
For shipping, the specimen may be kept at room temperature up to 2 days. The specimen can be stored at 2-8°C if it is to undergo assay within 5 days following collection. If longer periods are expected, the sample should be stored at -20 to -70°C. Analysis requires one day.
Tryptase is a trypsin-like proteinase that is found most abundantly in mast cells and basophils, with the former containing almost 300 times more tryptase. [8] As such, tryptase is specific to mast cell granules and can provide information about mast cell number, distribution, and activation depending on the clinical context. [9] Tryptase exerts sequential actions similar to histamine, namely as a vasoactive, pro-inflammatory, and chemotactic substance. [10]
The human tryptase gene is encoded on chromosome 16 and codes for four isoenzymes: alpha, beta, gamma, delta, and epsilon (Table 1). Of the four isoenzymes, beta tryptase is the predominant form stored in the mast cell granule where it is complexed as a tetramer stabilized by proteoglycans namely heparin. [11]
Table 1: Tryptase Types and Characteristics (Open Table in a new window)
Type
Characteristics
α-tryptase
Monomer:
Little biologic activity.
Constitutively secreted by mast cells in low concentrations even in the absence of degranulation
β-tryptase
Monomer:
Constitutively secreted with α-tryptase monomers
Tetramer:
Main storage form found in mast cell granules. Released during mast cell activation and degranulation
ϒ-tryptase
Monomer: membrane bound, unknown function
δ-tryptase
Monomer: short chain, unknown function
The enzymatically active mature tetramer is secreted with mast cell activation. In contrast, the immature monomeric form of beta tryptase is continuously secreted from the unstimulated mast cell and constitutes an individual’s baseline serum level. [12]
Upon stimulation from immunoglobulin E (IgE) released by plasma cells in response to allergens, mast cells release contents of their secretory granules to elicit tissue specific responses. Histamine and tryptase are the predominant mediators of these responses and are detectable in serum in as little as 15 minutes in experimental models of anaphylaxis.
Tryptase, however, diffuses at a slower rate into tissues than histamine, presumably because of its association with a large proteoglycan complex. Serum levels of tryptase peek in 1-2 hours after allergen provocation and can remain elevated for up to 12-24 hours. [6] In contrast, histamine levels return to baseline in 15-30 minutes. [13] As such, the longer biological half-life of tryptase (2 hours) makes it an attractive biological marker for episodes of mast cell activation.
Anaphylaxis
Anaphylaxis is a severe and potentially fatal systemic allergic reaction that occurs acutely after contact with an allergen. [14] It is classified under the Gell and Coombs hypersensitivity classification as a Type 1 immediate hypersensitivity reaction mediated by IgE release of histamine and other mediators, such as tryptase, through activated mast cells and basophils.
There is currently no laboratory test that can diagnose anaphylaxis in real time. However, measurement of mediators of the anaphylactic response can be measured to support the clinical diagnosis. Measurement of serum tryptase provides an ideal diagnostic tool as it can be detected within 15 minutes of the reaction and up to 3 hours thereafter. This is then compared to the patient’s baseline, which may be determined either prior to or at least 24 hours after the anaphylactic reaction. [6]
The utility of the test thus also extends to distinguish anaphylaxis from other forms of systemic shock, which are not mast cell mediated, such as cardiogenic shock, septic shock, neurogenic shock or obstructive shock.
Mastocytosis
Mastocytosis is a hematologic group of disorders characterized by accumulation of pathologic mast cells in different tissues such as the skin (urticarial pigmentosa), bone marrow, gastrointestinal tract, liver, spleen and lymph nodes. [15] The skin is the most common presenting organ involved and when mastocytosis is diffusely present in any extracutaneous tissue, it is called systemic mastocytosis. A set of diagnostic criteria was established by the World Health Organization (WHO) and includes determination of serum baseline tryptase as a criterion (Table 2). Baseline levels of serum tryptase reflect a patient’s mast cell burden as they detect the constitutively secreted inactive and monomeric forms of α and β tryptase.
Table 2: WHO Diagnostic Criteria for Systemic Mastocytosis (Open Table in a new window)
Major
Multifocal dense aggregates of mast cells with more than 15 cells per aggregate in an extracutaneous tissue.
Minor
Greater than 25% of mast cells have morphologic abnormalities such as spindle shapes, cytoplasmic projections, hypogranulation (see text)
Expression of CD25 with or without CD2 by mast cells
Detection of a codon 816 c-kit mutation by a sensitive technique in lesional tissue or peripheral blood
Serum baseline tryptase greater than 20 ng/mL*
The presence of either 1 major and at least 1 minor or 3 minor criteria provides a definitive diagnosis of systemic mastocytosis.
* does not apply to patients with an associated hematologic clonal non–mast-cell lineage disease
Of note, a basal tryptase level less than 20 ng/mL does not rule out the presence of mastocytosis. A recent study revealed that in indolent systemic mastocytosis, a subgroup of systemic mastocytosis in which bone marrow demonstrates abnormal collections of mast cells but not other end evidence of end organ damage, 5-7% of these patients will have serum tryptase less than 11.4 ng/mL. [16] Conversely, baseline levels slightly more than 20 ng/mL can be seen in other disease states, such as myeloid neoplasms and renal disease. As such, although elevated baseline serum tryptase more than 20 ng/mL strongly suggests the presence of mastocytosis, it should not be used as the sole criterion to diagnose mastocytosis. [15]
Baseline serum tryptase levels can give prognostic information in patients with systemic mastocytosis, in whom stable levels over time convey a good prognosis and rising levels indicate disease progression and poor prognosis. [17]
A progressive increase in serum tryptase in patients with systemic mastocytosis can also herald the transition to more aggressive forms such as mast cell leukemia. In these patients, serum tryptase levels are markedly elevated (often >500 ng/mL) and may increase rapidly (>100 ng/mL in a few weeks). [18]
Hypereosinophilic syndrome
Hypereosinophilic syndrome (HES) is a heterogeneous group of hematologic disorders classically defined by Chusid et al with the following criteria: 1) persistent eosinophilia (>1500 eosinophils/mm3 for at least 6 months) that is otherwise unexplained by a comprehensive evaluation 2) evidence of eosinophil related organ damage. [19]
Recent advances and expert consensus opinion have attempted to address limitations of these rigid definitions and recognize that tissue eosinophilia can exist in the absence of blood eosinophilia. Moreover, eosinophilia can be broadly defined as >1500 eosinophils/mm3 on two occasions at least one month apart. (Table 3). [20]
Table 3 (Open Table in a new window)
1. Hypereosinophilia—absolute eosinophil count >1,500 cells/μL for ≥1 mo, checked on ≥2 occasions.
Alternatively, tissue hypereosinophilia can be identified in addition to an elevated absolute eosinophil count with tissue hypereosinophilia, defined as:
i. Eosinophils >20% of nucleated cells in bone marrow
ii. Extensive tissue infiltration of target organ by histologic analysis
iii. Histologic evidence of eosinophil degranulation in a target tissue in the absence of eosinophils in that target tissue
2. Evidence of eosinophil-mediated target organ damage
3. Exclusion of all other potential causes of hypereosinophilia
Central to the evolving understanding of HES is the recent identification of subgroups with clonal populations of eosinophils or lymphocytes suggesting that HES can be divided into 2 major groups: those with a primary disorder of myelopoiesis and those with secondary cytokine mediated eosinophilia from a clonal population of lymphocytes. [21, 22]
In the myeloproliferative form of HES, the clonal molecular defect implicated is a deletion on chromosome 4q12 resulting in a fusion gene between Fip1-like (FIP1L1) and platelet-derived growth factor receptor-α (PDGFRA), leading to the production of a FIP1L1-PDGFRA fusion kinase. [23]
Since serum tryptase has been found to be elevated in some myeloproliferative disorders, primarily because of increased mast cell volume, the myeloproliferative variant of HES has also been shown to manifest elevated serum tryptase levels. [24]
However, there is considerable overlap between tryptase levels in myeloproliferative HES and systemic mastocytosis, and, as such, serum tryptase is not sensitive or specific enough to replace invasive molecular or flow procedures in the diagnosis of myeloproliferative HES.
Determination of serum tryptase level, in conjunction with other tests may provide additional information on HES. Specifically, a group of researchers found elevated tryptase levels were more common in HES patients with the FIP1L1-PDGFRA fusion gene, than those who did not. [25]
Serum tryptase may provide prognostic and predictive information in patients with HES. A study on a cohort of HES patients showed that patients with elevated serum tryptase had worse prognosis as they were more likely to develop fibroproliferative end organ damage and accelerated rates of death within 5 years. In contrast, all patients with normal serum tryptase levels were alive at 5 years. Moreover, the study also demonstrated that all patients with HES and elevated serum tryptase levels had a clinical and hematologic response when treated with Imatinib. This suggests that serum tryptase can be a marker for Imatinib responsiveness in HES patients. [26]
Other conditions
Several conditions have also been associated with increased baseline serum tryptase levels.
Thermo Scientific. ImmunoCAP Tryptase. Accessed May, 2014. [Full Text].
Komarow HD, Hu Z, Brittain E, Uzzaman A, Gaskins D, Metcalfe DD. Serum tryptase levels in atopic and nonatopic children. J Allergy Clin Immunol. 2009 Oct. 124(4):845-8. [Medline].
Belhocine W, Ibrahim Z, Grandne V, Buffat C, Robert P, Gras D. Total serum tryptase levels are higher in young infants. Pediatr Allergy Immunol. 2011 Sep. 22(6):600-7. [Medline].
Vitte J. Human mast cell tryptase in biology and medicine. Mol Immunol. 2014 May 2. [Medline].
Sargur R, Cowley D, Murng S, Wild G, Green K, Shrimpton A. Raised tryptase without anaphylaxis or mastocytosis: heterophilic antibody interference in the serum tryptase assay. Clin Exp Immunol. 2011 Mar. 163(3):339-45. [Medline].
Schwartz LB, Yunginger JW, Miller J, Bokhari R, Dull D. Time course of appearance and disappearance of human mast cell tryptase in the circulation after anaphylaxis. J Clin Invest. 1989 May. 83(5):1551-5. [Medline].
Rasp G, Hochstrasser K. Tryptase in nasal fluid is a useful marker of allergic rhinitis. Allergy. 1993 Feb. 48(2):72-4. [Medline].
Castells MC, Irani AM, Schwartz LB. Evaluation of human peripheral blood leukocytes for mast cell tryptase. J Immunol. 1987 Apr 1. 138(7):2184-9. [Medline].
Valent P. Mast cell activation syndromes: definition and classification. Allergy. 2013 Apr. 68(4):417-24. [Medline].
Miller HR, Pemberton AD. Tissue-specific expression of mast cell granule serine proteinases and their role in inflammation in the lung and gut. Immunology. 2002 Apr. 105(4):375-90. [Medline].
Dvorak AM. Ultrastructural analysis of human mast cells and basophils. Chem Immunol. 1995. 61:1-33. [Medline].
Caughey GH. Tryptase genetics and anaphylaxis. J Allergy Clin Immunol. 2006 Jun. 117(6):1411-4. [Medline].
van der Linden PW, Hack CE, Poortman J, Vivié-Kipp YC, Struyvenberg A, van der Zwan JK. Insect-sting challenge in 138 patients: relation between clinical severity of anaphylaxis and mast cell activation. J Allergy Clin Immunol. 1992 Jul. 90(1):110-8. [Medline].
Sampson HA, Muñoz-Furlong A, Campbell RL. Second symposium on the definition and management of anaphylaxis: summary report–Second National Institute of Allergy and Infectious Disease/Food Allergy and Anaphylaxis Network symposium. J Allergy Clin Immunol. 2006. 117(2):391-397.
Akin C, Valent P. Diagnostic criteria and classification of mastocytosis in 2014. Immunol Allergy Clin North Am. 2014 May. 34(2):207-18. [Medline].
Alvarez-Twose I, Zanotti R, González-de-Olano D, Bonadonna P, Vega A, Matito A. Nonaggressive systemic mastocytosis (SM) without skin lesions associated with insect-induced anaphylaxis shows unique features versus other indolent SM. J Allergy Clin Immunol. 2014 Feb. 133(2):520-8. [Medline].
Matito A, Morgado JM, Álvarez-Twose I, Sánchez-Muñoz L, Pedreira CE, Jara-Acevedo M, et al. Serum tryptase monitoring in indolent systemic mastocytosis: association with disease features and patient outcome. PLoS One. 2013. 8(10):e76116. [Medline]. [Full Text].
Valent P, Sotlar K, Sperr WR, Escribano L, Yavuz S, Reiter A. Refined diagnostic criteria and classification of mast cell leukemia (MCL) and myelomastocytic leukemia (MML): a consensus proposal. Ann Oncol. 2014 Mar 27. [Medline].
Chusid MJ, Dale DC, West BC, Wolff SM. The hypereosinophilic syndrome: analysis of fourteen cases with review of the literature. Medicine (Baltimore). 1975 Jan. 54(1):1-27. [Medline].
Valent P, Klion AD, Horny HP, Roufosse F, Gotlib J, Weller PF. Contemporary consensus proposal on criteria and classification of eosinophilic disorders and related syndromes. J Allergy Clin Immunol. 2012 Sep. 130(3):607-612.e9. [Medline].
Chang HW, Leong KH, Koh DR, Lee SH. Clonality of isolated eosinophils in the hypereosinophilic syndrome. Blood. 1999 Mar 1. 93(5):1651-7. [Medline].
Simon HU, Plötz SG, Dummer R, Blaser K. Abnormal clones of T cells producing interleukin-5 in idiopathic eosinophilia. N Engl J Med. 1999 Oct 7. 341(15):1112-20. [Medline].
Cools J, DeAngelo DJ, Gotlib J, Stover EH, Legare RD, Cortes J. A tyrosine kinase created by fusion of the PDGFRA and FIP1L1 genes as a therapeutic target of imatinib in idiopathic hypereosinophilic syndrome. N Engl J Med. 2003 Mar 27. 348(13):1201-14. [Medline].
Sperr WR, El-Samahi A, Kundi M, Girschikofsky M, Winkler S, Lutz D. Elevated tryptase levels selectively cluster in myeloid neoplasms: a novel diagnostic approach and screen marker in clinical haematology. Eur J Clin Invest. 2009 Oct. 39(10):914-23. [Medline].
Ogbogu PU, Bochner BS, Butterfield JH, Gleich GJ, Huss-Marp J, Kahn JE. Hypereosinophilic syndrome: a multicenter, retrospective analysis of clinical characteristics and response to therapy. J Allergy Clin Immunol. 2009 Dec. 124(6):1319-25.e3. [Medline].
Klion AD, Noel P, Akin C, Law MA, Gilliland DG, Cools J. Elevated serum tryptase levels identify a subset of patients with a myeloproliferative variant of idiopathic hypereosinophilic syndrome associated with tissue fibrosis, poor prognosis, and imatinib responsiveness. Blood. 2003 Jun 15. 101(12):4660-6. [Medline].
Chaldakov GN, Fiore M, Stankulov IS, Hristova M, Antonelli A, Manni L. NGF, BDNF, leptin, and mast cells in human coronary atherosclerosis and metabolic syndrome. Arch Physiol Biochem. 2001 Oct. 109(4):357-60. [Medline].
Cooper PJ, Schwartz LB, Irani AM, Awadzi K, Guderian RH, Nutman TB. Association of transient dermal mastocytosis and elevated plasma tryptase levels with development of adverse reactions after treatment of onchocerciasis with ivermectin. J Infect Dis. 2002 Nov 1. 186(9):1307-13. [Medline].
Costa JJ, Demetri GD, Harrist TJ, Dvorak AM, Hayes DF, Merica EA. Recombinant human stem cell factor (kit ligand) promotes human mast cell and melanocyte hyperplasia and functional activation in vivo. J Exp Med. 1996 Jun 1. 183(6):2681-6. [Medline].
Dugas-Breit S, Schöpf P, Dugas M, Schiffl H, Ruëff F, Przybilla B. Baseline serum levels of mast cell tryptase are raised in hemodialysis patients and associated with severity of pruritus. J Dtsch Dermatol Ges. 2005 May. 3(5):343-7. [Medline].
Liu J, Divoux A, Sun J, Zhang J, Clément K, Glickman JN. Genetic deficiency and pharmacological stabilization of mast cells reduce diet-induced obesity and diabetes in mice. Nat Med. 2009 Aug. 15(8):940-5. [Medline].
Moreno M, Puig J, Serrano M, Moreno-Navarrete JM, Ortega F, Ricart W, et al. Circulating tryptase as a marker for subclinical atherosclerosis in obese subjects. PLoS One. 2014. 9(5):e97014. [Medline]. [Full Text].
Sperr WR, Hauswirth AW, Valent P. Tryptase a novel biochemical marker of acute myeloid leukemia. Leuk Lymphoma. 2002 Dec. 43(12):2257-61. [Medline].
Sperr WR, Stehberger B, Wimazal F, Baghestanian M, Schwartz LB, Kundi M. Serum tryptase measurements in patients with myelodysplastic syndromes. Leuk Lymphoma. 2002 May. 43(5):1097-105. [Medline].
Type
Characteristics
α-tryptase
Monomer:
Little biologic activity.
Constitutively secreted by mast cells in low concentrations even in the absence of degranulation
β-tryptase
Monomer:
Constitutively secreted with α-tryptase monomers
Tetramer:
Main storage form found in mast cell granules. Released during mast cell activation and degranulation
ϒ-tryptase
Monomer: membrane bound, unknown function
δ-tryptase
Monomer: short chain, unknown function
Major
Multifocal dense aggregates of mast cells with more than 15 cells per aggregate in an extracutaneous tissue.
Minor
Greater than 25% of mast cells have morphologic abnormalities such as spindle shapes, cytoplasmic projections, hypogranulation (see text)
Expression of CD25 with or without CD2 by mast cells
Detection of a codon 816 c-kit mutation by a sensitive technique in lesional tissue or peripheral blood
Serum baseline tryptase greater than 20 ng/mL*
1. Hypereosinophilia—absolute eosinophil count >1,500 cells/μL for ≥1 mo, checked on ≥2 occasions.
Alternatively, tissue hypereosinophilia can be identified in addition to an elevated absolute eosinophil count with tissue hypereosinophilia, defined as:
i. Eosinophils >20% of nucleated cells in bone marrow
ii. Extensive tissue infiltration of target organ by histologic analysis
iii. Histologic evidence of eosinophil degranulation in a target tissue in the absence of eosinophils in that target tissue
2. Evidence of eosinophil-mediated target organ damage
3. Exclusion of all other potential causes of hypereosinophilia
Gentry George T King, MD Chief Resident, Department of Internal Medicine, Albert Einstein Medical Center
Gentry George T King, MD is a member of the following medical societies: Pennsylvania Medical Society, American Society of Clinical Oncology, Philippine Medical Association
Disclosure: Nothing to disclose.
Eric B Staros, MD Associate Professor of Pathology, St Louis University School of Medicine; Director of Clinical Laboratories, Director of Cytopathology, Department of Pathology, St Louis University Hospital
Eric B Staros, MD is a member of the following medical societies: American Medical Association, American Society for Clinical Pathology, College of American Pathologists, Association for Molecular Pathology
Disclosure: Nothing to disclose.
Anabella Lucca-Bianchi, MD Chief Resident, Department of Medicine, Albert Einstein Medical Center
Anabella Lucca-Bianchi, MD is a member of the following medical societies: Alliance for Academic Internal Medicine and American College of Physicians
Disclosure: Nothing to disclose.
Deepika Singh, MD Resident Physician, Department of Pediatrics, Albert Einstein Medical Center
Deepika Singh, MD is a member of the following medical societies: American Academy of Pediatrics
Disclosure: Nothing to disclose.
Serum Tryptase
Research & References of Serum Tryptase |A&C Accounting And Tax Services
Source