Comparison of Methacholine and Adenosine Inhalation Challenge in Patients with Suspected Asthma

Factors Associated with Positive Adenosine Challenge Test in Young Children with Suspected Asthma

Background: To investigate the predictive factors associated with positive adenosine monophosphate challenge using the auscultation method (AMP-PCW) test results. Methods: This is a prospective study of young children with suspected asthma who underwent AMP-PCW test. Patients with a positive AMP-PCW test were compared with those with a negative AMP-PCW. A multivariate logistic regression model was performed to identify the independent determinants of positive AMP-PCW. Results: A total of 159 patients completed the AMP-PCW test. The median age was 53 months. In total, 54.0% of patients had a positive AMP-PCW. The prevalence of atopic dermatitis and family history of asthma and allergy were significantly higher among the positive AMP-PCW group (P = 0.04, P = 0.02, and P = 0.007, respectively), as were the prevalences of elevated immunoglobulin E (IgE), peripheral blood eosinophils percentage (P = 0.003, P < 0.001, respectively), and number of emergency department (ED) visits/hospitalizations before AMP-PCW test (P = 0.006). A significant inverse correlation exists between peripheral blood eosinophils percentage and serum IgE levels with the AMP end-point concentrations (r = -0.302, P = 0.001, and r = -0.312, P = 0.001, respectively). In multivariate logistic regression model, peripheral blood eosinophils percentage, IgE levels, and the number of ED visits/hospitalizations before the AMP-PCW test were found as independent predictors for positive AMP-PCW test result. Conclusions: Our results suggest that bronchial responsiveness to AMP-PCW is related to proxy markers of airway inflammation (elevated eosinophils and IgE levels) and clinical exacerbation of asthma before the test. This may support the role of AMP-PCW in detecting inflammatory changes and monitoring their trend among young children with suspected asthma.

Comparison of bronchial hyperresponsiveness to methacholine and adenosine and airway inflammation markers in patients with suspected asthma

BACKGROUND

Bronchial hyperresponsiveness is usually measured by bronchial challenge test with direct (e.g., methacholine) and indirect (e.g., adenosine) agonists. There are few studies comparing both types of agents and they have had conflicting concordance.

OBJECTIVE

We sought to compare the results of both tests in a population with symptoms suggestive of asthma so as to determine their relationship with bronchial inflammatory markers.

METHODS

Seventy-nine patients whose age ranged from 14 to 81 years were recruited for this study. Challenge tests were performed using the tidal volume method. PC₂₀ methacholine and PC₁₅ and PC₂₀ adenosine were calculated. Induced sputum and fraction of exhaled nitric oxide measurements were also performed.

RESULTS

Atopy was found in 69% of the patients. Methacholine PC₂₀ and adenosine PC₁₅ were positive in 32 patients (40.5%), both having a sensitivity of 73%. Percentage of agreement was 45.45% and κ index was only 0.369. Adenosine PC₂₀ elicited lower sensitivity and agreement. No correlation between methacholine PC₂₀ and adenosine PC₁₅ was observed. Higher fraction of exhaled nitric oxide values and sputum eosinophil counts were seen in patients with positive adenosine challenge results. The use of adenosine PC₁₅ or PC₂₀ did not alter the association with inflammatory markers.

CONCLUSIONS

The concordance between both techniques was low. Methacholine is not a reliable predictor of hyperresponsiveness to adenosine, leading us to conclude that the two tests are complementary but not interchangeable in clinical practice. Additionally, responsiveness to the two bronchoconstrictor stimuli does not indicate presence of the same airway abnormality. Indirect stimuli provide a better reflection of bronchial inflammation.

The effect of caffeinated coffee on airway response to methacholine and exhaled nitric oxide

BACKGROUND

The bronchoprotective effect of caffeine on histamine challenge testing (HCT) has been studied with equivocal results. Current guidelines for bronchoprovocation testing recommend exclusion of caffeine the day of testing. The effects of caffeine on methacholine challenge testing (MCT), now more commonly performed than histamine challenge, are unknown.

METHODS

Sixteen well-controlled asthmatics with a forced expiratory volume in 1 s (FEV(1)) > 65% predicted and methacholine provocation concentration causing a 20% fall in FEV(1) (PC(20)) ≤ 16 mg/ml participated in a randomized single-blind crossover study. The two treatments included 16 ounces of caffeinated and decaffeinated coffee given on two separate days. The fraction of exhaled nitric oxide (eNO) and FEV(1) were measured before and 1 h after each treatment. One hour post treatment blood was drawn for serum caffeine level and the MCT was done.

RESULTS

Fourteen subjects completed the study; there were no adverse events. No significant bronchodilation was seen between the mean FEV(1) values before and after the caffeinated treatment (3.31 ± 0.75 L and 3.36 ± 0.74 L, respectively). No significant bronchoprotection was seen between the caffeinated and decaffeinated treatment's geometric mean PC(20) values (1.35 mg/ml and 1.36 mg/ml, respectively). Mean eNO values before and after caffeinated treatment were not significantly different (31.2 ± 19.6 ppb and 31.5 ± 20.4 ppb).

CONCLUSION

The amount of caffeine in a normal dietary serving of a 16 oz cup of coffee is not enough to cause significant bronchoprotection, bronchodilation, or decrease eNO values. Registered at http://clinicaltrials.gov: NCT01057875.

Usefulness of exhaled nitric oxide for diagnosing asthma

RATIONALE

A standard asthma diagnosis is made based on clinical history, reversibility of airway obstruction, and bronchial hyperresponsiveness. Fractional exhaled nitric oxide (FeNO) is a noninvasive airway inflammatory marker that has been suggested as a diagnostic tool for asthma. The aim of this study was to establish a FeNO cut-off value for asthma diagnosis.

METHODS

One hundred and fourteen consecutive adult patients (mean age 34 ± 13 years) reporting symptoms consistent with asthma, with normal spirometric parameters and a negative bronchodilator test, were included in the study. All underwent a methacholine challenge test following the five-breath dosimeter protocol. FeNO was measured with a portable device (NioxMino, Aerocrine AB, Sweden) just before the methacholine challenge. The sensitivity, specificity, and diagnostic performance of FeNO measurement were calculated.

RESULTS

Thirty-five out of the 114 patients (30.7%) were diagnosed with asthma. A positive methacholine challenge was associated with higher FeNO levels and with lower forced expiratory volume in one second (FEV(1)) at baseline. No correlation was found between methacholine provocative concentration causing a decrease of 20% in FEV(1) (PC(20)) and FeNO levels. A receiver-operating characteristic curve was constructed for FeNO levels (area under the curve [AUC]: 0.762; 95% confidence interval [CI]: 0.667-0.857; p < .001). The FeNO cut-off point with maximal specificity and sensitivity for asthma diagnosis was 40 ppb.

CONCLUSIONS

Patients with confirmed asthma showed higher FeNO levels. A cut-off value of 40 ppb was calculated as the most efficient for asthma diagnosis in our population. The use of FeNO measurement may be a helpful tool to rule out a diagnosis of asthma, especially in patients in whom a methacholine challenge is not feasible or available.