Middle-aged smokers should have phlegm tests to increase their chances of detecting lung disease early, the University of Hong Kong warned yesterday. The warning for smokers aged 40 to 60 to take a sputum cytology test, where two samples of phlegm are taken, follows a landmark study by HKU doctors into the testing. If the test turns up abnormal cells, patients need to undergo a bronchoscopy, after which nearly all cases of central airway lung cancer can be detected. Lam Bing, honorary clinical assistant professor at HKU's department of medicine, said middle-aged smokers should take the tests because they were the group most commonly found with the disease. Central airway cancer is a common cancer among smokers, and accounts for about 20 per cent of all lung cancer cases in Hong Kong. 'Most lung cancer patients do not have any symptoms and only discover their disease in the final stage,' Dr Lam said. 'The sputum cytology test is useful to detect lung cancer in an earlier stage, thus lowering the mortality rate.' Screening can increase the number of lung cancer cases detected in early stages from about 20 per cent to 46.2 per cent, Dr Lam said. The university began its study in 2002, inviting 181 smokers over 40 for sputum tests. Of those, 110 were found to have abnormal cells and 85 underwent bronchoscopies, with lung cancer confirmed in seven cases. Of the 25 who did not have bronchoscopy tests, one was diagnosed with the final stage of lung cancer 26 months after the screening. Of the 21 cases whose sputum was normal, four were discovered to have another form of lung cancer, adenocarcinoma, after being followed up for 3? years. Dr Lam said the sputum test could miss 95 per cent of the second form of cancer, which was much more easily detected with a CT scan. A sputum test is cheaper and less intrusive than a bronchoscopy, and a bronchoscopy may not detect some smaller cancerous lesions. Lung cancer is the world's top cancer killer and kills more than 4,000 people in Hong Kong each year. One patient, Mr Kwan, 73, who was diagnosed with lung cancer in 2002 after going through the screening, beat the disease but still needs to go for annual check-ups. He started smoking when he was 11 and smoked as many as three packets a day. 'I don't dare smoke now because my doctors and family have been scolding me too much.'