Community-acquired Pneumonia - Diagnosis

Diagnosis

Individuals with symptoms of CAP require further evaluation. Physical examination by a health provider may reveal fever, an increased respiratory rate (tachypnea), low blood pressure (hypotension), a fast heart rate (tachycardia), and/or changes in the amount of oxygen in the blood. Feeling the way the chest expands (palpation) and tapping the chest wall (percussion) to identify dull areas which do not resonate can identify areas of the lung which are stiff and full of fluid (consolidated). Examination of the lungs with the aid of a stethoscope can reveal several things. A lack of normal breath sounds or the presence of crackling sounds (rales) when the lungs are listened to (auscultated) can also indicate consolidation. Increased vibration of the chest when speaking (tactile fremitus) and increased volume of whispered speech during auscultation of the chest can also reveal consolidation.

X-rays of the chest, examination of the blood and sputum for infectious microorganisms, and blood tests are commonly used to diagnose individuals with suspected CAP based upon symptoms and physical examination. The use of each test depends on the severity of illness, local practices, and the concern for any complications resulting from the infection. All patients with CAP should have the amount of oxygen in their blood monitored with a machine called a pulse oximeter. This helps determine how well the lungs are able to work despite infection. In some cases, analysis of arterial blood gas may be required to accurately determine the amount of oxygen in the blood. Complete blood count (CBC), a blood test, may reveal extra white blood cells, indicating an infection. Chest x-rays and chest computed tomography (CT) can reveal areas of opacity (seen as white) which represent consolidation. A normal chest x-ray makes CAP less likely; however, CAP is sometimes not seen on x-rays because the disease is either in its initial stages or involves a part of the lung not easily seen by x-ray. In some cases, chest CT can reveal a CAP which is not present on chest x-ray. X-rays can often be misleading, as many other diseases can mimic CAP such as heart problems or other types of lung damage.

Several tests can be performed to identify the cause of an individual's CAP. Blood cultures can be drawn to isolate any bacteria or fungi in the blood stream. Sputum Gram's stain and culture can also reveal the causative microorganism. In more severe cases, a procedure wherein a flexible scope is passed through the mouth into the lungs (bronchoscopy) can be used to collect fluid for culture. Special tests can be performed if an uncommon microorganism is suspected (such as testing the urine for Legionella antigen when Legionnaires' disease is a concern).