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EPIC CODE: 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)


Performing Laboratory

Mayo Clinic Laboratories in Rochester

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


Day(s) Performed

Monday through Friday

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

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.


The diagnosis of Legionnaires disease cannot be based on clinical or radiological evidence alone. There is no single satisfactory laboratory test for Legionnaires disease. Culture results, serology, and antigen detection methods should all be used in conjunction with clinical findings for diagnosis.


The Legionella pneumophila serogroup 1 will not detect infections caused by other serogroups, Legionella micdadei or Legionella longbeachae. Culture is recommended for suspected pneumonia to detect causative agents other than L pneumophila serogroup 1 and to confirm infection.


Excretion of Legionella antigen in urine may vary among patients, depending on their underlying illness or treatment. Some individuals have been shown to excrete antigen for extended periods of time (up to 1 year after acute infection) and positivity may, therefore, indicate previous infection rather than current infection. Early treatment with appropriate antibiotics may decrease antigen excretion in some individuals, and the use of diuretics may affect the ability of the test to detect antigen. Consequently, patient history (eg, a history of a recent respiratory illness compatible with Legionnaires disease) must be considered when evaluating results.

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 Description

The BINAXNOW Legionella Urinary Antigen Test is an immunochromatographic membrane assay to detect Legionella pneumophila serogroup 1 soluble antigen in human urine. Rabbit anti-L pneumophila serogroup 1 antibody (the patient line) is adsorbed onto nitrocellulose membrane. Goat-anti-rabbit IgG (the control line) is adsorbed onto the same membrane as a second stripe. Rabbit anti-L pneumophila serogroup 1 antibodies are conjugated to visualizing particles that are dried onto an inert fibrous support. The resulting conjugate pad and the striped membrane are combined to construct the test strip. This test strip and a well to hold the swab specimen are mounted on opposite sides of a hinged, book-shaped test device.


To perform the test, a swab is dipped into the urine specimen, removed, and then inserted into the test device. Reagent A is added from a dropper bottle. The device is then closed, bringing the specimen into contact with the test strip. L pneumophila serogroup 1 urinary antigen captured by immobilized anti-L pneumophila serogroup 1 antibody reacts to bind conjugated antibody. Immobilized goat-anti-rabbit IgG also captures visualizing conjugate, forming the control line. A positive test result is visually read in 15 minutes or less depending on the concentration of antigen present in the urine specimen. A negative result, read in 15 minutes, indicates that L pneumophila serogroup 1 antigen was not detected in the urine specimen.


The test is interpreted by the presence or absence of visually detectable pink-to-purple colored lines. A positive result will include the detection of both a patient and a control line, while a negative assay will produce only the control line. Failure of the control line to appear, whether the patient line is present or not, indicates an invalid assay.(Package insert: BinaxNow Legionella Urinary Antigen Card. Abbott Diagnostics; IN852050 Rev.12, 01/2021)

Report Available

Same day/1 day

Specimen Retention Time

14 days

Reject Due To

Gross hemolysis Reject
Turbid Dyes/unnaturally colored Reject

NY State Approved


Method Name

Immunochromatographic Membrane Assay

Secondary ID



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)