Depends. Depends on the cause.. Chronic coughs are often caused by post-nasal drip, asthma, or even reflux (gerd). Of course infection is always a possibility, so blood work and an x-ray may need to be done. Sometimes medications (ace-inhibitors for example) can cause a dry, nagging cough. For any blood, you may need a ct or even a bronchoscopy - a lighted camera - ma need to be used.