Antibody to *Escherichia coli* O157:H7 (IgG) – Serology
This test detects antibodies in your blood that your immune system produces in response to exposure to *Escherichia coli* O157:H7, a strain of bacteria often linked to foodborne illness.
["This test helps identify past exposure to a harmful bacterial strain that may cause severe illness."]
Key facts at a glance
- LOINC
- 865-6
- Short code
- Deprecated A3 Ab Ser Ql
- Synonyms
- Deprecated A3 Ab Ser Ql
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- aggl-rbc
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
What This Test Measures
The test looks for IgG antibodies specific to the O157:H7 antigen of *E. coli*. These antibodies indicate your immune system has encountered the bacteria at some point, though you may not have had symptoms or may have recovered from an infection. IgG antibodies remain in your blood for longer than other types of antibodies and can persist even after the infection has cleared.
Why It’s Done
Doctors may order this test if you’ve had symptoms like severe diarrhea, vomiting, or bloody stools—common signs of *E. coli* O157:H7 infection—especially after exposure to contaminated food or water. It can also be used in outbreaks or when investigating foodborne illness clusters.
How It Works
A small blood sample is taken from your arm. The lab analyzes it using an immunoassay method to detect the presence of IgG antibodies against the *E. coli* O157:H7 antigen. This process identifies whether your immune system has recognized the bacteria.
What the Results Mean
A positive result means your body has produced antibodies to *E. coli* O157:H7, suggesting past exposure. A negative result means no detectable antibodies were found at this time, but this does not definitively rule out infection. Antibody levels may take weeks to develop after exposure, so results should be interpreted in the context of your symptoms and medical history.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
E. coli O157:H7 Antibody (IgG)
Frequently asked questions
This test is primarily used to diagnose or investigate past exposure to *E. coli* O157:H7, which can cause life-threatening conditions like hemolytic uremic syndrome (HUS) in some individuals. While antibodies indicate exposure, they do not confirm an active infection. Doctors may use this test alongside other diagnostic tools, such as stool cultures, to guide treatment and prevent further spread.
What does a positive result mean? A positive result means your immune system has likely encountered *E. coli* O157:H7 at some point, but it does not confirm an active infection. You may have recovered from an infection years ago, or the exposure may have been asymptomatic.
How long does it take to get results? Results are typically available within 1 to 3 business days, depending on your lab’s processing schedule.
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy