Pneumonia Testing

Types of Pneumonia Tests

Various types of pneumonia tests may be performed based on a patient’s symptoms and overall health. In most cases, initial testing for pneumonia involves a physical examination, medical history review, and a chest x-ray. These steps often allow for an initial diagnosis to be made.

Recommendations for further testing are tailored to a patient’s situation. In general, patients who have more severe symptoms, may require hospitalization, or who are at higher risk of complications are more likely to undergo additional pneumonia testing.

The following sections provide details about the different types of tests that may be involved in the diagnosis and evaluation of pneumonia.

Medical history review and physical exam

Pneumonia testing usually begins with an initial examination by a doctor that includes both a review of your medical history and a physical exam. This process helps the doctor understand your situation, check for signs of pneumonia, and look for the possible complications of an infection.

A medical history review includes a discussion of your current symptoms as well as your overall health and medical history. The doctor will usually ask about how long you have had symptoms and may ask questions about your medications, vaccinations, if you have been around other people who are sick, if you smoke cigarettes, or if you have other health issues that may affect your risk for pneumonia.

A physical exam for pneumonia typically includes using a stethoscope to listen to your lungs. A health care provider may tap on your chest and ask you to take several breaths while they listen. During this exam, the doctor is checking to see if they hear certain sounds that are associated with pneumonia.

Most of the time, additional tests are needed after this clinical evaluation. In some situations, a medical history review and physical exam may be sufficient to diagnose mild cases of pneumonia.

Chest imaging tests

If your medical history review and physical exam suggest pneumonia, the doctor will normally suggest an imaging test to look more closely at your lungs.

A chest x-ray is the typical imaging test used to diagnose pneumonia. This testing can show the presence of a pneumonia infection in the lungs.

Although less often used in pneumonia testing, a computed tomography (CT) scan of the chest may be considered in select situations. A CT scan provides more detailed images and are usually used when the initial chest x-ray has unexpected results, if symptoms are abnormal, or if symptoms may be explained by another lung condition.

In some hospitals and medical offices, an ultrasound of the lung may be used to help diagnose pneumonia. This method of imaging is not as common, but it may be most useful when it is otherwise difficult to perform a chest x-ray or CT scan.

Tests to assess overall health

Because pneumonia can trigger a range of potential complications, it is common for tests that assess your overall health to be included as part of pneumonia testing. Examples of these tests include:

• Complete blood count (CBC) with differential: This test measures the amount of each type of blood cell in a blood sample taken from a vein in your arm. In addition to providing insight about overall health, a CBC can show if there is an elevated level of white blood cells, which is associated with some infections.
• Basic metabolic panel (BMP): This is another routine blood test that assesses kidney function, electrolytes, and blood sugar levels.

Tests to assess lung function

Pneumonia directly affects the lungs, so the doctor may recommend one or more pulmonary function tests to check how well your lungs are working to provide oxygen to your body.

One type of pulmonary function test is pulse oximetry, which checks whether there is enough oxygen in your blood. The test uses a sensor clipped to your ear or finger that estimates your blood oxygen levels.

Another way of evaluating your blood oxygen levels is with an arterial blood gases test. This test uses a sample of blood taken from an artery and measures the amount of oxygen, blood pH, and carbon dioxide.

Tests to find the cause of pneumonia

Pneumonia testing may include a range of tests to identify why pneumonia occurred. There are many potential causes of pneumonia including an infection with a bacteria, virus, or fungus. When the cause is known, the doctor can choose a tailored therapy that offers the most benefit and least risk.

This kind of testing is not routinely performed in patients with mild cases of pneumonia. Trying to identify the cause is of greater importance when a patient is hospitalized or at higher risk of severe complications from pneumonia.

Although many tests are available to look for the underlying cause, in the majority of cases, no single cause can be conclusively identified.

The following sections describe different types of tests that may be used to detect the cause of pneumonia. Each section is organized based on the type of sample that is used for testing.

Sputum tests

Sputum is a thick kind of mucus produced in the lungs that is also known as phlegm. It is distinct from saliva or spit because its thickness helps it trap and remove pathogens from the lungs. For this reason, sputum can be analyzed to check for signs of bacteria, viruses, or other pathogens.

There are three main ways that a sputum sample can be obtained. The least invasive way of collecting sputum is by coughing deeply so that sputum can be spit into a cup. Before this, you may inhale a vapor that makes it easier to produce a testable amount of sputum.

When this method fails to produce sufficient sputum, other procedures may be necessary:

• Bronchoscopy: This is a procedure that inserts a flexible scope with a camera into the lungs. This allows the doctor to look more closely at the inside of the lungs. During the test, a small brush may collect a sputum sample, or a saline solution can be used to wash a sample of sputum out so that it can be analyzed. This procedure is known as bronchoalveolar lavage.
• Lung biopsy: This is a surgery that involves removing a sample of tissue from the lung. A lung biopsy is rarely necessary for pneumonia and is generally reserved for special cases and less common types of pneumonia.

Once a sputum sample has been collected, there are a number of different ways that it may be analyzed:

• Culture: In a sputum culture test, the lab places sputum in a special dish for a few days to see if bacteria or other infectious germs grow. If they do, the lab may be able to identify the specific bacteria or other pathogen that caused pneumonia.
• Gram stain: A Gram stain involves applying a purple-colored substance, known as the Gram stain, to the sample. Depending on how the sample changes color, it can indicate the type of infection present. A sputum gram stain may be repeated multiple times over several days, and it can be combined with a sputum culture test.
• Fungal smear: A fungal smear looks for presence of a fungal infection by examining a sputum sample under a microscope.
• Polymerase chain reaction (PCR): PCR is a type of molecular test that uses special laboratory techniques to check for the presence of the genetic material of a pathogen in a sputum sample. These tests can look for one or more kinds of bacteria or viruses.
• Direct fluorescent antibody (DFA): A sputum DFA test requires adding a fluorescent dye to a sputum sample that is then looked at under a special microscope. When certain infections are present, the sample will appear to glow.

Throat or nasal swab tests

Some tests use a swab of the throat, nostrils, or the area at the back of the nose to look for viruses that can cause respiratory symptoms and pneumonia.

Most people with pneumonia are tested for influenza and, during the global COVID-19 pandemic, the SARS-CoV-2 virus that causes COVID-19. Depending on a patient’s symptom severity and risk factors, swab tests may be used to look for other respiratory viruses.

Blood tests

Blood tests can be used to try to determine the cause of pneumonia.

Blood culture tests involve using a blood sample to try to grow bacteria in a lab. The test usually takes a few days to see if any bacteria grow, at which point they can be identified and targeted for treatment. Blood cultures can also detect possible complications such as an infection that has entered the bloodstream.

Another type of blood test that may be prescribed is a beta-D-glucan test. Beta-D-glucan is part of the cell walls of fungi, so this test can help detect a fungal infection that may have caused pneumonia.

Sometimes pneumonia testing may include blood tests that look for procalcitonin or C-reactive protein (CRP). These are substances in the blood that are associated with inflammation. These tests may be used to help distinguish between causes of inflammation and to assess a patient’s response to treatment.

Urine tests

A urine sample can be analyzed for the presence of two bacteria that can cause pneumonia, Streptococcus pneumoniae and Legionella pneumophila. These tests work by looking for antigens, which are substances found on the surface of the bacteria that trigger an immune response.

Pleural fluid tests

Sometimes pneumonia can be tied to the buildup of liquid in the pleura, which is the area between the wall of the chest and the lining on the outside of the lungs.

In a procedure called thoracentesis, a sample of this fluid can be removed by inserting a needle through the chest wall and into the pleural space. In a pleural fluid test, this sample can be analyzed under a microscope or used to try to culture bacteria in the laboratory in order to look for an underlying infection causing pneumonia.