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HelpTest ID: LAGU Legionella Antigen, Random, Urine
Reporting Name
Legionella Ag, UUseful 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.
Interpretation
Positive:
Positive for Legionella pneumophila serogroup 1 antigen in urine, suggesting current or past infection. Culture is recommended to confirm infection.
Negative:
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
1 to 2 daysDay(s) Performed
Monday through Friday
Clinical Reference
1. Berdal BP, Farshy CE, Feeley JC. Detection of Legionella pneumonophila antigen in urine by enzyme-linked immunospecific assay. J Clin Microbiol. 1979;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;297(22):1189-1197
3. Stout JE, Yu VL. Legionellosis. N Engl J Med. 1997;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
UrineOrdering 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
Negative
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
87899
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 |
Forms
If not ordering electronically, complete, print, and send 1 of the following with the specimen:
-Infectious Disease Serology Test Request (T916)
-Microbiology Test Request (T244)
mml-respiratoryinfections