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Beta-lactamase production in *Escherichia coli* (qualitative screening for extended-spectrum beta-lactamase, ESBL)

Published: August 9, 2026Updated: August 16, 2026

This test checks if your blood contains bacteria (*E. coli*) that produce enzymes called beta-lactamases, which may make certain antibiotics less effective against them.

Quick summary

["Helps determine if antibiotics like cephalosporins or penicillins may not work well against your infection."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
85834-0
Short code
ESBL blaCTX-M9 Grp gene Islt/Spm Ql
Synonyms
ESBL blaCTX-M9 Grp gene Islt/Spm 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
molgen
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

Why This Test Is Done

Your healthcare provider may order this test if you have a urinary tract infection (UTI), bloodstream infection, or other serious infection where *E. coli* is suspected. It helps guide antibiotic treatment to ensure the right medicine is chosen.

What to Expect Before the Test

No special preparation is needed. The blood sample is typically drawn from a vein in your arm. If you’re taking antibiotics, let your provider know—it may affect results.

How the Test Works

A small amount of your blood (serum/plasma) is tested for the presence of beta-lactamase enzymes. This is done using an immunoassay method to detect the specific proteins that break down certain antibiotics.

Possible Results and Next Steps

A positive result means your *E. coli* bacteria may produce ESBL, which could require different antibiotics. A negative result suggests standard antibiotics may work. Your provider will discuss treatment options based on the results.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

ESBL in E. coli (serum/plasma)

Frequently asked questions

If ESBL is present, your infection may not respond well to first-line antibiotics like ampicillin or cephalosporins. This can lead to treatment failures or the need for broader-spectrum antibiotics, which may have more side effects.
A positive test result helps healthcare providers choose the most effective antibiotic to treat your infection and avoid unnecessary exposure to less effective drugs.
How long will I need to wait for results?
Results are usually available within 1–3 business days, depending on your lab. Your provider will contact you with the outcome and next steps.
Can I take antibiotics before getting this test?
Yes, but inform your provider immediately. Antibiotics before testing may affect the accuracy of the ESBL result, so they may need to adjust your treatment plan accordingly.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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