A Review of Similarities and Differences Between 2 Different Cough Tests

Researchers found the combination of the cough suppression test and the cough challenge test may help physicians detect chronic refractory cough (CRC) in patients, according to a review published in Therapeutic Advances in Respiratory Disease.

The cough challenge test is the most widely used test for CRC and is based on identifying sensitization of a patient’s peripheral cough-related receptors. It requires the patient to inhale aerosol participles, such as capsaicin, which causes an atomization of cough. The patient is then instructed to cough freely without any attempt to suppress their cough.

Cough sensitivity is then measured by the minimum concentration of tussive agent needed to cause 2 coughs (C2) or 5 coughs (C5). The decrease of C5 indicates an enhanced cough sensitivity.

The cough suppressant test is based on the standard cough challenge test but instructs the patient to try to suppress their cough during testing, and then records the concentrations of tussive agent causing 1 cough (CS1), 2 coughs (CS2), and 5 coughs (CS5). Furthermore, a decrease of CS5 suggests a decrease in cough suppression function, which may be due to central nervous system circuit disorders.

To compare these 2 tests, the researchers evaluated each test’s repeatability, association with the subjective quality of life scale, follow-up value, interference factors, and the value or CRC identification.

As a result, the researchers found the cough challenge test had good reproducibility and sensitivity, but the diagnostic value was limited, which affects its clinical application. On the other hand, the cough suppression test showed higher sensitivity, higher specificity, and better repeatability than the cough challenge test in identifying patients with chronic cough, especially patients with CRC.

Th researchers believe that the combination of both tests may show the greatest ability in identifying and detecting chronic cough, as the cough challenge test is the most widely accepted test and has good sensitivity, while the cough suppressant test furthers that sensitivity.

Lastly, the researchers believe that further studies should examine the combination of these 2 tests to further physician understanding in identifying and treating chronic cough.

“The cough challenge test and the cough suppression test have many similarities in methodology and complement each other in mechanism and application,” concluded the researchers. “The combination of these 2 tests can play an important role in the chronic cough research.”

Reference

Zhao K, Bai X, Wen S, Wang S, Xu X, Yu L. Similarities and differences between the cough suppression test and the Cough Challenge Test. Therapeutic Advances in Respiratory Disease. 2023;17:175346662311622. doi:10.1177/17534666231162246