Which test is recommended for diagnosing asthma in a patient with recurrent nighttime coughing and wheezing?

Spirometry testing is the recommended method for diagnosing asthma, particularly in a patient presenting with symptoms such as recurrent nighttime coughing and wheezing. This test measures the volume of air a person can forcefully exhale after taking a deep breath, providing critical information about lung function.

In individuals with asthma, spirometry typically shows reversible airflow obstruction; this means that after the administration of a bronchodilator (a medication that relaxes and opens the airways), the patient should demonstrate an improvement in their lung function measurements. This characteristic response is a hallmark of asthma. Additionally, spirometry can help determine the severity of the asthma, which is important for treatment planning.

Peak expiratory flow meter monitoring, while useful for ongoing management and monitoring of asthma, does not provide the comprehensive assessment needed for a definitive diagnosis. Bronchoprovocation with methacholine is a specialized test used in certain cases, especially when the diagnosis is uncertain, but it is not the first-line test for typical asthma diagnosis. Chest x-rays can be used to rule out other conditions contributing to respiratory symptoms but do not provide direct information about asthma itself or its severity.