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Table 3 Role of Laboratory Tests in the Diagnosis of Anaphylaxis

From: World Allergy Organization Guidelines for the Assessment and Management of Anaphylaxis

Total tryptase (pro, pro', and mature forms of alpha/beta tryptases)
   Obtain blood sample within 15 minutes to 3 hours of symptom onseta, b
   Consider measuring levels in accurately timed serial blood samples during the anaphylactic episode
   Consider comparing levels measured during the episode with a baseline levelc, d
   Obtain blood sample within 15 minutes to 1 hour of symptom onseta
   Special handling of the blood sample is required (use wide-bore needle, keep sample at 4°C and centrifuge it promptly, freeze plasma promptly)
   Measure histamine and its metabolite N-methylhistamine in a 24-hour urine sample
  1. aTryptase levels can also be elevated acutely in myocardial infarction, trauma, amniotic fluid embolus, sudden infant death syndrome and other diseases; histamine levels can also be elevated in scombroid poisoning (usually affects more than 1 person eating the same fish).
  2. bTryptase levels can be measured in postmortem serum, preferably in blood samples obtained from femoral vessels rather than the heart. The levels need to be correlated with the clinical history because increased levels are also found in patients who die from other conditions such as myocardial infarction unrelated to anaphylaxis, trauma, amniotic fluid embolism, and sudden infant death syndrome. Conversely, levels can be within normal limits in patients with clinically documented anaphylaxis.
  3. cObtained either 24 hours after resolution of the acute episode or on frozen serum, if available; tryptase levels are stable for at least 1 year in sera stored at -20°C.
  4. dIf tryptase level is > 11.4 ng/mL in baseline serum, the diagnosis of mastocytosis or clonal mast cell disorder should be considered; if tryptase level is higher during the acute anaphylactic episode than in baseline serum, the diagnosis of anaphylaxis is confirmed; if tryptase level is within normal limits during a clinically diagnosed acute anaphylactic episode, the normal tryptase level cannot be used to rule out the diagnosis.
  5. eAlthough not universally available, other specific laboratory tests might be needed to rule out carcinoid syndrome, paradoxical response to a pheochromocytoma, and other uncommon entities in the differential diagnosis of anaphylaxis.
  6. Adapted from references [3, 24, 4244, 50, 51, 90].