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Test Code SLEG Legionella pneumophila (Legionnaires Disease), Antibody, Serum

Reporting Name

Legionella Pneumophila Ab, S

Useful For

Evaluation of possible legionellosis (Legionnaires disease, Pontiac fever, extrapulmonary legionella infection caused by Legionella pneumophila)

Performing Laboratory

Mayo Medical Laboratories in Rochester

Specimen Type

Serum


Specimen Required


Collection Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Specimen Volume: 0.5 mL


Specimen Minimum Volume

0.4 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Refrigerated (preferred) 14 days
  Frozen  14 days

Reference Values

Negative

Day(s) and Time(s) Performed

Tuesday, Thursday; 2 p.m.

Test Classification

This test has been cleared or approved by the U.S. 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

86713

LOINC Code Information

Test ID Test Order Name Order LOINC Value
SLEG Legionella Pneumophila Ab, S In Process

 

Result ID Test Result Name Result LOINC Value
SLEG Legionella Pneumophila Ab, S 7947-5

Clinical Information

Legionella pneumophila may cause pulmonary disease in both normal and immunocompetent hosts. The disease may occur sporadically in the form of community acquired pneumonia and in epidemics. Pneumonia (often referred to as Legionnaires disease) occurs more frequently in severely immunosuppressed individuals; a milder form of the illness, referred to as Pontiac fever, is more prevalent in normal hosts. Extrapulmonary infection with Legionella pneumophila is rare. Legionnaire's disease, Pontiac fever, and extrapulmonary infection have been collectively referred to as legionellosis.

 

Approximately 85% of the documented cases of legionellosis have been caused by Legionella pneumophila. Serogroups 1 and 6 of Legionella pneumophila, by themselves, account for up to 75% of cases of legionellosis.

 

The definitive diagnosis of Legionella pneumophila is made by isolation of the organism on specialized culture medium (buffered charcoal yeast extract agar). Pulmonary secretions can be directly examined using a direct fluorescent antibody procedure, but the sensitivity of this method is low (25%-70%). Often it is difficult for the patient to produce pulmonary secretion (sputum) for examination, the pneumonia is frequently interstitial and sputum is scant. In the absence of invasive procedures (eg, bronchial alveolar lavage), urine evaluation for Legionella pneumophila antigen or indirect serological (antibody) methods may be useful.

Interpretation

A negative result indicates that IgG/A/M antibody to Legionella pneumophila serogroups 1-6 is not detected. Negative results do not exclude Legionella infection. It may require 4 to 8 weeks to develop a detectable antibody response; serum specimens taken early in the course of infection may not yet have significant antibody titers. Furthermore, antibody levels can fall to undetectable levels within a month of infection, early antibiotic therapy may suppress antibody response, and some individuals may not develop antibodies above detectable limits.

 

Some culture-positive cases of Legionella do not develop Legionella antibody.

 

Positive results are suggestive of Legionella infection; however, a single positive result only indicates immunologic exposure at some time. It does not distinguish between previous or current infection. The level of antibody response may not be used to determine active infection. Other laboratory procedures or additional clinical information are necessary to establish a diagnosis.

 

Specimens with equivocal results are retested prior to reporting. Repeat testing on a second specimen should be considered in patients with equivocal results, if clinically indicated.

Clinical Reference

1. Color Atlas and Textbook of Diagnostic Microbiology. Fifth edition Lippincott. Edited by EW Koneman, SD Allen, WM Janda, et al: Philadelphia, Lippincott-Raven Publishers 1997

2. Principals and Practice of Infectious Diseases. Third edition. Edited by GL Mandell, RG Douglas, JE Bennett. Churchill Livingston, 1990

Analytic Time

Same day/1 day

Reject Due To

Hemolysis

Mild OK; Gross reject

Lipemia

Mild OK; Gross reject

Icterus

NA

Other

NA

Method Name

Enzyme-Linked Immunosorbent Assay (ELISA)