A doctor who suspects pneumonia begins by taking a thorough medical history and performing a physical examination. Bacterial pneumonias often come on suddenly; creating a cough that produces mucous that is often colored or "rusty", fever, and pain along the chest wall.
Infections caused by the Mycoplasma pneumoniae species of bacteria and viruses tend to develop more slowly, after a few days of flu-like symptoms. They can cause a hacky or barky cough, headache, and pain under the breastbone.
The Physical Examination
The most important diagnostic tool for pneumonia may be the stethoscope. In pneumonia, as air passes through mucous and fluids in the lungs, it creates sounds called rales and rhonchi. The doctor will strongly suspect pneumonia if rales are heard on one side of the chest and while the patient is lying down.
The doctor may also tap lightly on the person's chest, a diagnostic tool called "percussion". A dull thud instead of a hollow drum-like sound may indicate that the lung has become firm and inelastic from inflammation, called consolidation; or that fluid may be collecting in between the layers of the lung membrane, called pleural effusion.
Several tests may be ordered to help in the diagnosis:
Chest x-rays may show signs of infection in the lungs. Different types of pneumonia often will have different patterns on the x-ray.
Blood and sputum tests may be performed to collect a specimen if the doctor needs to determine the organism causing the pneumonia.
A lung biopsy may be performed in severe cases.
Other Diagnostic Procedures
In persons with life-threatening pneumonias more aggressive diagnostic procedures may be required.
Thoracentesis is done to remove and analyze fluid from the pleura, the thin membrane that lines the outside of the lung and the chest cavity. Any accumulation of fluid between the layers of the pleura is called a pleural effusion. Fluid in the pleura is withdrawn using a long thin needle inserted between the ribs and analyzed in the laboratory.
A bronchoscopy may be performed if the physician wants to see inside the lung. In this test, a tube is inserted through the nose or mouth. The tube acts like a telescope into the body, allowing the physician to view the wind-pipe and major airways for pus, abnormal mucous, or other problems.
The physician may ask you to breathe into an instrument called a spirometer that measures the amount of air you breathe. This test, called a spirometry, can help to determine how well the lungs are functioning.
Some of the bacteria that can cause pneumonia, such as Legionella, Mycoplasma, and Chlamydia, cannot be seen with an ordinary microscope. They are found using special culture techniques or by performing blood tests that detect antibodies to the organisms.
Aspiration pneumonias cause changes in the chest x-ray that can be seen six to 24 hours after inhalation. Symptoms include respiratory distress indicated by grunting, cough, and fever after the aspiration of hydrocarbons, foreign substances, or bodily fluids. Symptoms may develop in minutes or hours depending on the volume and nature of the aspirated substance.