Laboratory parameters of the 1st order – obligatory laboratory tests.
- Small blood count (due toleukocytes/white blood cells) or CRP (C-reactive protein) – for inflammation diagnosis.
- Differential blood count: determination of absolute eosinophil count [eosinophilia// eosinophilic and non-eosinophilic asthma: supports the diagnosis of bronchial asthma; COPD: usually low, eosinophilia may be present in the exacerbation phase] (see “Further notes” below).
- Allergen diagnostics (to detect allergic asthma/extrinsic asthma).
- Prick test (skin test; method of choice): in this procedure, the allergens in question are applied in droplet form to the forearms. A thin needle is then used to slightly nick the skin at these sites, allowing the test solution to enter the skin. This is only slightly painful – only the top layer of skin is scratched. If erythema (reddening of the skin over a large area) or wheals appear after about 15 to 30 minutes, the test is positive. However, a positive test result only indicates that sensitization to the substance has occurred. However, the substance does not have to be the triggering allergen. Therefore, other investigations such as the provocation test usually follow to confirm the result.
- Antibody detection (useful supplement to the prick test if skin test is not possible (eczema, hypersensitive skin with positive reaction to the solvent, lack of reaction of the skin to histamine, lack of test substance), or the result is not clearly readable (eg, dermographism)):
- Ig-E detection (= total IgE or allergen-specific IgE in serum) – if allergy of the immediate type (type I) is suspected; especially if a skin test (see above) is difficult to perform or would put the patient at risk.
- Precipitating IgG antibodies (allergy type III).
- If necessary nasal provocation test (NPT) (indication: prick test and specific Ig E is negative)Here, for example, nasal sprays, which contain pollen suspected of allergy, are sprayed on the nasal mucosa. Since hay fever is an allergy of the immediate type, the typical hay fever symptoms occur immediately if the allergy is present. After the allergen has been applied in the NPT, the altered nasal air passage (“through the nose“) is measured using anterior rhinomanometry (measurement and analysis of the volume flow passing through the nasal cavity during breathing) – to detect local allergic rhinitis (LAR)Another provocation test exploits the reaction of the conjunctiva (conjunctivae) to allergen exposure. This test is suitable as a predictor of symptoms of allergic rhinoconjunctivitis during a pollen season.Insofar as inhaled allergens are a possible cause of bronchial asthma, inhaled provocation tests (bronchial provocation) are indicated in individual cases.
Note: Diagnostic exposure scarcity may provide evidence of an allergen (eg, animals in the household; occupational environment). Laboratory parameters 2nd order – depending on the results of the history, physical examination, etc. – for differential diagnostic clarification.
- Blood gas analysis (ABG) – to investigate pulmonary function [art. Blood gases – asthma: normal between exacerbations; COPD: abnormal between exacerbations of severe COPD]
- IgG subclasses (humoral immunity) IgG subclass deficiency: regulatory defects, primary synsthesis disorder (indication: refractory bronchial asthma).
- Vitamin D, copper, zinc – biomarkers for determining the risk of asthma in patients with recurrent wheezing.
- In infection exacerbation:
- Bacteriology (cultural) sputum, tracheal secretions, bronchial secretions for pathogens and resistance.
- Antigen detection: influenza, respiratory syncytial virus (RSV), mycoplasma, Legionella if necessary.
- Direct detection (PCR): Legionella pneumophila, Chlamydophila pneumoniae, Mycoplasma pneumoniae, Bordetella pertussis/parapertussis, Bocaparvovirus (until 2015 Bocavirus), Adenovirus, Rhinovirus, Influenza typeA/typeB, parainfluenza type 1,2,3, respiratory syncytial virus (RSV), human metapneumovirus, human coronaviruses, enteroviruses (coxsackie, polio, picorna, ECHO).
- Serology: detection of antibodies against chlamydia, adenoviruses, coxsackie viruses, ECHO viruses, influenza A/B viruses, parainfluenza viruses, respiratory syncytial virus (RSV).
- Periostin determination in sputum – Periostin is considered a biomarker for phenotypes of severe asthma.
- Blood gas analysis (BGA) – to investigate lung function in severe courses.
- Alpha-1 antitrypsin – to exclude alpha-1 antitrypsin deficiency in bronchial asthma with not fully reversible airway narrowing.
Further notes
- According to the S2k guideline: diagnosis and therapy of patients with asthma, “detection of more than 300 eosinophils/μl of blood at least twice should be aimed for to verify the presence of eosinophilic asthma.” Note: Thresholds for eosinophilia differ by antibody-based therapy, depending on criteria in pivotal trials (mepolizumab ≥ 150, benralizumab ≥ 300, reslizumab ≥ 400 eosinophils/μl blood).
- Note: Oral cortisol therapy, as well as high doses of inhaled corticosteroids (ICS), may result in undetectable eosinophilia in blood and tissue.