The onset of a chronic cough at age 70 is worrisome. Your father should have a chest X-ray and a culture of his phlegm. He should also have sputum cytology, and a blood count, to look for signs of infection. If the recommended tests do not reveal a cause of his cough he should have an evaluation of his upper airways and sinuses. If this is negative, he may require a
bronchoscopyBronchoscopy
Bronchoscopy with transbronchial biopsy. The cough you describe could originate anywhere in his respiratory system, from the sinuses (post-nasal drip) on down. It could be caused by infection, a tumor or even by
aspirationAspiration
Bone marrow aspiration
Joint aspiration
Lung needle biopsy
Meconium aspiration syndrome
Skin lesion aspiration
Synovial fluid analysis
Thoracentesis of a foreign body, such as food.
It is important for a new-onset, chronic cough that persists for months be thoroughly evaluated, especially when the person is elderly and even more so if there is a history of cigarette smoking.
JCI RRT RCP
--a good Pulmonologist (lung doc) to find out what's causing the cough & phlegm,
--a good ENT (Ear, nose & throat doc), also to find causes of the cough & phlegm,
--a good GI (Gastro-intestinal doc), in case the cough & phlegm are partially caused by gastric reflux,
--the doctor who prescribed the insulin for the diabetes,
--the doctor who prescribed the blood pressure medication,
And I encourage you to make sure that these docs talk to eachother, so each one knows what the others discovered, when they speak to and examine and test your father.
Bring your ideas and the others' suggestions to these docs & see what they think is going on.
I wish your father the best. I hope he gets correctly diagnosed and treated soon!