I always cough up stuck phlegm from throat...sometime the colour are changed and today I see small red dot.I am really scare.I already went to two doctors,one was General medicine doctor who says it was due to pollution and one was Ent doctor who think it might be post nasal drip.I take their prescription medication but the my problem was not solved.So,i want to know is there internal infection.I also want to test my sputum. As there are many type of sputum test I want to know which type of sputum test should I do.there are some types of sputum test in picture attached to this.Please reply me which test should I pick