The methacholine test (synonym: methacholine provocation test; English : methacholine challenge test) is a nonspecific, inhalation (for inhalation) provocation test used in pneumology (pulmonary medicine) and allergology for the diagnosis of bronchial asthma. With the help of the method it is possible to assess bronchial hyperreactivity (excessive readiness of the airways to react to an exogenous stimulus (e.g. cold air, inhalation toxins), which leads to pathological narrowing of the airways (bronchoobstruction)) in the context of asthma. The increased sensitivity of the bronchial mucosa is a contributing factor to the symptomatology of asthma. As a result of this hyperresponsiveness, stimuli that would not elicit a response in a physiologic (healthy) bronchial system can cause asthma symptoms such as dry cough, dyspnea (shortness of breath), and wheezing (breath sounds). Methacholine itself is a drug in the parasympathomimetic group (increasing the parasympathetic nervous system) that can cause irritation of the bronchial system in a dose-dependent manner.
Indications (areas of application)
- Bronchial asthma – determination of the degree of bronchial hyperresponsiveness is part of asthma diagnosis and can be used to assess asthma.
Contraindications
Absolute contraindications
- Allergy to methacholine – In the presence of allergy to methacholine, the procedure should not be performed. As a rule, other parasympathomimetics are not used because of possible cross-reactivity.
- Concomitant cardiovascular disease – A cardiovascular disease that is an absolute contraindication is bradycardic arrhythmia (slowing of the heart rate).
- Exacerbation of asthma – in the case of acute worsening of symptoms, the test should be abandoned.
- Pregnancy (gravidity) – the use of methacholine may affect the development of the fetus, so the procedure can not be used in pregnant patients under any circumstances.
Relative contraindications
- Airway obstruction – in the case of airway obstruction (narrowing or obstruction of the airway), depending on the severity, the methacholine test is not performed. From a moderate degree of severity, the procedure is usually not used.
- Children – in children under five years of age, the procedure should usually be omitted.
Before the examination
- Caffeine – until 2011, it was recommended to avoid caffeine intake and thus coffee consumption before the examination because caffeine, as a theophylline analog (similar effect to the asthma drug theophylline), can attenuate the bronchial response. However, one study demonstrated that caffeine intake prior to the study had no effect on bronchial hyperresponsiveness. In the study, a defined level of caffeine was achieved, but it had no effect on the main target parameter “forced one-second capacity (FEV1)”.
- Refraining from asthma medications – when performing the methacholine test, in consultation with the treating pulmonologist (lung specialist), it is necessary to refrain from taking medications that could result in an influence on the test results. Example substances that should not be used are short-acting beta-sympathomimetics (among other things, improving the widening of the airways) such as salbutamol and fenoterol and anticholinergic substances such as ipratroprium bromide and tiotropium bromide. Anti-allergic substances such as the histamine H1 receptor antagonist loratadine, various beta-blockers such as metoprolol and inhaled glucocorticoids (cortisone and other preparations) should also be discontinued before the test.
The procedure
Various methods are possible to carry out the procedure:
- 5-step test-This method of assessing bronchial hyperresponsiveness is the American Thoracic Society recommended performance of the methacholine test. Prior to the methacholine test, spirometry (a medical procedure to determine the volume of breath and lungs) is also performed. Five different concentrations of methacholine (0.0625; 0.25; 1.0; 4.0; 16 mg/ml) are prepared and administered to the patient via a nebulizer.Spirometry is used to determine FEV1 (forced one-second capacity) 90 seconds after administration of methacholine. The step test is relatively complex in the implementation.
- 4-step test – Considered a further development of the 5-step test, the 4-step test requires only one concentration of methacholine to be prepared and administered. This concentration is administered four times and FEV1 is then determined.
After the examination
Due to the irritation of the bronchial system, moderate to severe stress should be avoided initially following the examination. However, there are no special measures to be taken after the methacholine test.
Possible complications
- Asthma attack – During the methacholine test, a strong reaction of the bronchial system is possible, so dyspnea and wheezing up to asthma attack may occur. Due to this, it is essential to perform the procedure under medical supervision.
- Allergic reactions – an allergic reaction as a result of ingestion of methacholine is possible.
- Cardiovascular complications – after inhaled application (administration) of methacholine, there is a possibility of a drop in diastolic blood pressure and the patient becoming tachycardic (increased heart rate).
- Vegetative side effects – nausea and vomiting as consequences of the procedure may occur.
- Pneumothorax – in rare cases, an air gap may form in the pleural space that requires immediate medical evaluation and treatment.
