Legionella Ag, URN (Sendout)

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

Ordering Note: For use by non-UW Medicine patients only. For UW Medicine patients, refer to test Legionella Antigen, Urine [ULEG].

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.

Cautions:

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.

Outside Laboratories: Transfer 0.5 mL urine to a separate screw-capped plastic vial. Refrigerate urine. Do not centrifuge.

Stability: Refrigerated (preferred) 7 days; Frozen 14 days; Ambient 24 hours.

Reject Due To: Gross hemolysis, turbid dyes/unnaturally colored samples. Excessively bloody or very turbid specimens containing protein, cells, or particulates will be canceled. They can inhibit the function of the test.

Transfer 0.5 mL urine into a screw-capped, plastic urine tube. Refrigerate urine. Do not centrifuge.

Sendouts:

• Order Mayo Test: LAGU.
• Interfaced: Yes.

Stability: Refrigerated (preferred) 7 days; Frozen 14 days; Ambient 24 hours.

Reject Due To: Gross hemolysis, turbid dyes/unnaturally colored samples. Excessively bloody or very turbid specimens containing protein, cells, or particulates will be canceled. They can inhibit the function of the test.