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Test ID: LAGU Legionella Antigen, Random, Urine

Reporting Name

Legionella Ag, U

Useful For

An adjunct to culture for the detection of past or current Legionnaires disease (Legionella pneumophila serogroup 1)


Clinical Information

Legionnaires disease, named after the outbreak in 1976 at the American Legion convention in Philadelphia, is caused by Legionella pneumophila and is an acute febrile respiratory illness ranging in severity from mild illness to fatal pneumonia. Since that time, it has been recognized that the disease occurs in both epidemic and endemic forms, and that sporadic cases are not readily differentiated from other respiratory infections by clinical symptoms. It is estimated that about 25,000 to 100,000 Legionella infections occur annually. Known risk factors include immunosuppression, cigarette smoking, alcohol consumption, and concomitant pulmonary disease. The resulting mortality rate, which ranges up to 40% in untreated immunocompetent patients, can be lowered if the disease can be rapidly diagnosed and appropriate antimicrobial therapy instituted early. L pneumophila is estimated to be responsible for 80% to 85% of reported cases of Legionella infections with the majority of cases being caused by L pneumophila serogroup 1 alone.


A variety of laboratory techniques (culture, direct fluorescent antibody, DNA probes, immunoassay, antigen detection), using a variety of specimen types (respiratory specimens, serum, urine), have been used to help diagnose Legionella pneumonia. Respiratory specimens are preferred. Unfortunately, one of the presenting signs of Legionnaires disease is the relative lack of productive sputum. This necessitates the use of invasive procedures to obtain adequate specimens (eg, bronchial washing, transtracheal aspirate, lung biopsy) in many patients. Serology may also be used but is often retrospective in nature.


It was shown as early as 1979 that a specific soluble antigen was present in the urine of patients with Legionnaires disease.(1) The presence of Legionella antigen in urine makes this an ideal specimen for collection, transport, and subsequent detection in early, as well as later, stages of the disease. The antigen may be detectable in the urine as early as 3 days after onset of symptoms.



Positive for Legionella pneumophila serogroup 1 antigen in urine, suggesting current or past infection. Culture is recommended to confirm infection.



Negative for L pneumophila serogroup 1 antigen in urine, suggesting no recent or current infection. Infection with Legionella cannot be ruled out because:

-Other serogroups (other than serogroup 1, which is detected by this assay) and other Legionella species (other than L pneumophila) can cause disease

-Antigen may not be present in urine in early infection

-The level of antigen may be below the detection limit of the test


Legionella culture is recommended for cases of suspected Legionella pneumonia due to organisms other than L pneumophila serogroup 1.

Report Available

Same day/1 day

Day(s) Performed

Monday through Friday

Clinical Reference

1. Berdal BP, Farshy CE, Feele JC: Detection of Legionella pneumophila antigen in urine by enzyme-linked immuno-specific assay. J Clin Microbiol. 1979 May;9(5):575-578

2. Fraser DW, Tsai TR, Orenstein W, et al: Legionnaires' disease: description of an epidemic of pneumonia. N Engl J Med. 1977 Dec 1;297(22):1189-1197

3. Stout JE, Yu VL: Legionellosis. N Engl J Med. 1997 Sept 4;337(10):682-687

4. Edelstein PH, Roy CR: Legionnaires disease and Pontiac fever. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Elsevier; 2020:2807-2817

Method Name

Immunochromatographic Membrane Assay

Specimen Type


Ordering Guidance

This assay has been verified using urine specimens only. For serum specimens, order SLEG / Legionella pneumophila (Legionnaires Disease), Antibody, Serum.


Other specimen types (eg, plasma or body fluids) that may contain Legionella antigen have not been verified for testing.

Specimen Required

Supplies: Urine Tubes, 10 mL (T068)

Container/Tube: Plastic, 10-mL urine tube

Specimen Volume: 0.5 mL

Collection Instructions:

1. Collect a random urine specimen.

2. No preservative.

3. Excessively bloody or very turbid specimens containing protein, cells, or particulates will be canceled. They can inhibit the function of the test.

4. Centrifuging to remove particulates is not approved.

5. Specimens with any dyes or unnatural color are not acceptable and will be canceled.

Specimen Minimum Volume

0.25 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Urine Refrigerated (preferred) 7 days
  Frozen  14 days
  Ambient  24 hours

Reference Values


Test Classification

This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
LAGU Legionella Ag, U 32781-7


Result ID Test Result Name Result LOINC Value
81268 Legionella Ag, U 32781-7


If not ordering electronically, complete, print, and send 1 of the following with the specimen:

-Infectious Disease Serology Test Request (T916)

-Microbiology Test Request (T732)

Mayo Clinic Laboratories | Microbiology and Infectious Disease Catalog Additional Information: