Beta-Lactamase (Extended-Spectrum) Activity in Serum/Plasma (Qualitative or Quantitative)
This test measures how your body’s blood produces an enzyme that can break down certain antibiotics, helping doctors choose the right treatment for infections.
["Helps determine if bacteria are resistant to common antibiotics like penicillin or cephalosporins."]
Key facts at a glance
- LOINC
- 73438-4
- Short code
- Clavulanate ind plt IgM SerPl Ql FC
- Synonyms
- Clavulanate ind plt IgM SerPl Ql FC
- Category
- hematology
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- flow-cytometry
- CPT
- 86038
- 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 Matters
Antibiotics like amoxicillin or cephalexin work by blocking bacterial enzymes called beta-lactamases. If your body produces high levels of this enzyme, bacteria may become resistant to these drugs, requiring alternative treatments. This test helps guide antibiotic selection to improve infection outcomes.
What to Expect Before the Test
No special preparation is needed unless instructed by your healthcare provider. You may have a small needle inserted into your arm to draw blood. If you’re on blood thinners, let your doctor know before the test.
How the Test Works
Blood is collected and tested for beta-lactamase activity using an immunoassay or enzymatic method. The test checks whether the enzyme is present and, if so, whether it can break down specific antibiotics. Results are qualitative (positive/negative) or quantitative (measuring enzyme activity levels).
Possible Results and Their Meaning
A positive result means your blood contains beta-lactamase, which may indicate bacterial resistance to certain antibiotics. A negative result suggests the bacteria are less likely to be resistant to those antibiotics. Your doctor will interpret results in the context of your infection and medical history.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Beta-lactamase activity is critical for diagnosing antibiotic resistance in infections caused by bacteria like *E. coli*, *Klebsiella*, or *Staphylococcus*. High levels of this enzyme can render common antibiotics ineffective, prompting doctors to prescribe broader-spectrum or alternative antibiotics. Early detection helps prevent unnecessary antibiotic use and reduces the risk of antibiotic-resistant infections.
Short name
Beta-lactamase enzyme activity test
Frequently asked questions
What does a positive beta-lactamase test mean?
How long does it take to get results?
Can I take antibiotics before this test?
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