What is the role of blood tests in the workup of asthma?

Updated: Oct 07, 2019
  • Author: John J Oppenheimer, MD; Chief Editor: Michael A Kaliner, MD  more...
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Blood tests (in vitro) for allergen-specific IgE, such as ImmunoCAP, may be used in place of skin testing if dermatologic disease is generalized, if antihistamine or TCA use cannot be suspended (which affects skin testing but not in vitro testing), or if skin testing is relatively contraindicated. However, skin testing is more specific, more sensitive, and usually less expensive than in vitro testing.

The serum IgE level is elevated only approximately half the time in patients with allergic disease. Obtaining an IgE level is not indicated in most patients with asthma, although levels greater than 1000 ng/mL (1 IU= 2.4 ng) may suggest an alternate diagnosis, such as allergic bronchopulmonary aspergillosis. Confounding illness, such as atopic dermatitis, may also result in high IgE levels. IgE levels are also important in tandem with proof of perennial allergic sensitization when considering the addition of omalizumab (anti-IgE).

Serum eosinophil counts may be useful if considering using anti-IL5 biologic agents (mepolizumab, reslizumab, and benralizumab). Other tests, which are not commercially available, have been looked at, such as serum periostin and enterotoxin-specific IgE. A study that explored immunological determinants associated with severe refractory asthma found that the mean level of enterotoxin-specific IgE was 3-fold higher in patients with severe asthma compared with patients with nonsevere asthma (P = 0.01). [19] It was also significantly associated with low respiratory function parameters (FEV1, FEV1/FVC, and MEF 25/75) and increased airway reversibility in response to albuterol. This suggests a role for staphylococcal enterotoxins in the asthma pathogenesis

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