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Legionella Pneumophila Antigen Blood Test

Last updated May 9, 2019

Approved by: Maulik P. Purohit MD, MPH

The Legionella Pneumophila Antigen Blood Test detects characteristic molecules made by L. pneumophila and not the host. It is used to identify infection by L. pneumophila.

What are the other Names for this Test? (Equivalent Terms)

  • L. Pneumophila Antigen Blood Culture Test
  • Legionella Pneumophila Ag Blood Test
  • Legionella Pneumophila Antigen Blood Culture Test

What is Legionella Pneumophila Antigen Blood Test? (Background Information)

  • Legionella pneumophila, or L. pneumophila, is a species of bacteria that causes legionellosis, also known as Legionnaire’s disease. The Legionella Pneumophila Antigen Blood Test is a method of detecting L. pneumophila in blood
  • L. pneumophila live in watery environments. They are resistant to chlorine and heat. They are often found in warm (35-45°C), stagnant bodies of water and in air-conditioning ducts
  • The bacterium travel through the air encapsulated in water droplets called aerosols. They cause infection after being inhaled. They are not spread from one individual to another, or through swimming, or drinking contaminated water
  • The most common sources of L. pneumophila are air-conditioning ducts. The bacteria grow and multiply inside a protective film called a biofilm. They then become aerosolized and are rendered inhalable. After inhalation, L. pneumophila invade immune cells of the lungs called macrophages. They then live in them as ‘in-cell’ parasites
  • In most individuals, the resulting legionellosis, or Legionnaire’s disease, consists of mild cold-like symptoms or no symptoms at all. A healthy immune system can clear away the infection without the need for medical attention
  • However, certain individuals have a weakened immune system and are more susceptible to serious pneumonia caused by L. pneumophila. These individuals include the elderly, those undergoing immunosuppressive therapy, and individuals infected by HIV
  • The symptoms of Legionnaire’s disease are often initially intestinal, such as diarrhea or constipation. Respiratory symptoms then follow, along with muscle aches, if the disease progresses. The condition is treated using antibiotics; most commonly using erythromycin, administered intravenously
  • The Legionella Pneumophila Antigen Blood Test detects characteristic molecules made by L. pneumophila and not the host. It is used to identify infection by L. pneumophila

What are the Clinical Indications for performing the Legionella Pneumophila Antigen Blood Test?

Following are the clinical indications for performing the Legionella Pneumophila Antigen Blood Test:

  • Diarrhea
  • Cramps, muscle aches
  • Sore throat
  • Headache
  • Fever, chills
  • Fatigue
  • Shortness of breath
  • Chest pain
  • Joint stiffness
  • Increased sweating

How is the Specimen Collected for Legionella Pneumophila Antigen Blood Test?

Following is the specimen collection process for Legionella Pneumophila Antigen Blood Test:

Sample required: Blood

Process of obtaining blood sample in adults:

  • A band is wrapped around the arm, 3-4 inches above the collection site (superficial vein that lies within the elbow pit)
  • The site is cleaned with 70% alcohol in an outward spiral, away from the zone of needle insertion
  • The needle cap is removed and is held in line with the vein, pulling the skin tight
  • With a small and quick thrust, the vein is penetrated using the needle
  • The required amount of blood sample is collected by pulling the plunger of the syringe out slowly
  • The wrap band is removed, gauze is placed on the collection site, and the needle is removed
  • The blood is immediately transferred into the blood container, which has the appropriate preservative/clot activator/anti-coagulant
  • The syringe and the needle are disposed into the appropriate “sharp container” for safe and hygienic disposal

Preparation required: No special preparation is needed prior to the test.

What is the Significance of the Legionella Pneumophila Antigen Blood Test Result?

  • A positive Legionella Pneumophila Antigen Blood Test may indicate infection by L. pneumophila

The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.

Additional and Relevant Useful Information:

  • Legionnaire’s disease is named after an outbreak of pneumonia in 1976 during an American Legion convention in Philadelphia, Pennsylvania. 34 out of the 221 infected people died
  • Prior to 2007, Legionnaire’s disease was rare (4-6 reported cases per million people in the US). However in 2007, 8 cases per million, or 2716 cases, were reported in the US. This is either due to an increased infection rate or a better recognition of the disease

Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider of the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

  • Atypical pneumonia is a type of lung infection that is caused by specific types of bacteria including Legionella pneumophila

The following article link will help you understand atypical pneumonia:


Please visit our Laboratory Procedures Center for more physician-approved health information:


References and Information Sources used for the Article:

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Sept. 7, 2015
Last updated: May 9, 2019