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Extended-spectrum β-lactamase (ESBL) detection in serum/plasma by immunoassay

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

This test helps identify if certain bacteria in your bloodstream may produce enzymes called ESBL, which can make antibiotics less effective. It’s often used when infections are resistant to standard treatments.

Quick summary

["ESBL detection can guide better antibiotic choices for infections."]

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

Key facts at a glance

LOINC
85840-7
Short code
ESBL blaVEB gene Islt/Spm Ql
Synonyms
ESBL blaVEB 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 Might Be Ordered

Your doctor may recommend this test if you have a bacterial infection that doesn’t respond well to common antibiotics like penicillin or cephalosporins. It’s also used in monitoring patients with recurring infections or those who’ve been exposed to antibiotics that ESBL-producing bacteria can resist.

How the Test Works

The test uses an immunoassay (a lab method that detects specific proteins) to check for ESBL enzymes in your serum or plasma. If ESBL is present, it can interfere with certain antibiotics, so this test helps confirm whether those antibiotics will be effective.

Sample Collection and Preparation

A blood sample is drawn from your arm, and the serum or plasma is separated and sent to the lab for testing. This test is typically done on fresh or stored plasma/serum samples.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to avoid certain medications (like some antibiotics) for a short time before testing if instructed by your doctor.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

ESBL Screening (Serum/Plasma)

Frequently asked questions

What does a positive or negative result mean?
A positive result means your blood sample contains ESBL enzymes, which may suggest the bacteria causing your infection could be resistant to certain antibiotics. This doesn’t always mean you’ll need a different antibiotic right away—your doctor will consider other factors like infection type and severity. A negative result means ESBL enzymes were not detected, but other antibiotic resistance mechanisms could still be present.
How often is this test repeated?
This test is usually done once, but your doctor may order it again if you have recurring infections or if you’re being treated for an infection that doesn’t improve with standard antibiotics. Follow your doctor’s instructions for follow-up testing.
Can I take antibiotics before this test?
If your doctor has ordered this test, they may advise against taking certain antibiotics (like cephalosporins) for a few days before testing to get the most accurate result. Always follow their specific instructions.
  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