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Diagnostic Test – Legionella Urine Antigen
​1. What is this?

The Legionella urine antigen test detects antigen from Legionella pneumophila in the urine. It is a rapid, noninvasive test and is considered the best initial test to make a specific diagnosis of Legionella pneumonia.

2. What is the best test?

  • The urine antigen test has ~100% specificity for Legionella pneumophila serogroup 1.
  • However, only 70–80% of Legionella infections are caused by serogroup 1.
  • Therefore, the definitive diagnostic test is:
    • Sputum culture or tracheal aspirate culture on buffered charcoal yeast extract (BCYE) agar.
3. When do I answer Legionella urine antigen

Choose Legionella urine antigen when the clinical scenario shows:

  • Pneumonia in a nursing home resident or recent hospitalization
  • High fever
  • Confusion
  • Diarrhea
  • Hyponatremia
  • Possible lab abnormalities:
    • ↑ Creatine phosphokinase (CPK)
    • ↑ Liver function tests
    • ↑ Creatinine
This classic constellation strongly suggests Legionella pneumonia, and the urine antigen is the best initial diagnostic test.


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Kembara Xtra 

Facts about medicine and its subtopic such as anatomy, physiology, biochemistry, pharmacology, medicine, pediatrics, psychiatry, obstetrics and gynecology and surgery.