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Cefoxitin Disk Diffusion Test for Beta-Lactamase Production (Microbiology Culture)

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

This test checks whether bacteria in your blood sample produce an enzyme called beta-lactamase, which can make certain antibiotics less effective. It helps doctors determine if your infection may require different treatment.

Quick summary

["This test helps identify bacteria resistant to cefoxitin, guiding antibiotic choices for your infection."]

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

Key facts at a glance

LOINC
101492-7
Short code
CEFOX-MIC-VOC
Synonyms
cefOXitin Bld Pos MIC.VOC det
Category
chemistry
Sample
whole-blood
Container
Positive blood culture bottle (aerobic and/or anaerobic) — typically BacT/ALERT, BACTEC, or equivalent continuous-monitoring blood culture system
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
0–120 years
Method
mic-voc-detection
CPT
87186
SNOMED
104215004
Specimen volume
Not applicable; testing performed directly from positive blood culture broth (typically 0.5–1 mL aliquot drawn from flagged positive bottle)
Stability
Test should be performed within 8 hours of blood culture bottle flagging positive. If delayed, store positive bottle at room temperature (20–25°C); do not refrigerate.
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why This Test Is Done

Your doctor may order this test if you have a suspected bacterial infection that could be caused by bacteria producing beta-lactamase. This enzyme breaks down beta-lactam antibiotics, including cefoxitin, which is sometimes used to treat serious infections. The test helps ensure the right antibiotic is chosen to treat your infection effectively.

How the Test Works

A small amount of your blood sample is mixed with bacteria from your infection. Cefoxitin antibiotic disks are placed on the sample. If bacteria produce beta-lactamase, they grow around the disks where the antibiotic is broken down. This growth is measured to determine if the bacteria are resistant.

Sample Collection

A blood sample is collected from a vein, usually in your arm, by a healthcare professional. This is a simple procedure that may cause a slight pinch or discomfort but is generally quick and painless.

Test Results and Interpretation

Results are qualitative (yes/no) and indicate whether the bacteria in your sample produce beta-lactamase. If positive, it suggests the bacteria may be resistant to cefoxitin and other beta-lactam antibiotics. Your doctor will discuss the results and any necessary changes to your treatment plan.

Reference range

Interpretive criteria based on CLSI M100 guidelines. Susceptible (S): MIC ≤ 8 μg/mL for Enterobacterales; ≤ 16 μg/mL for Staphylococcus spp. Intermediate (I): MIC 16 μg/mL for Enterobacterales. Resistant (R): MIC ≥ 32 μg/mL for Enterobacterales. Results are reported as S/I/R with associated MIC value.N/A

Specimen: whole-blood

No special patient preparation required. Sample is collected as part of standard blood culture collection when bacteremia or fungemia is suspected.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Beta-lactamase-producing bacteria can make certain antibiotics ineffective, leading to treatment failures. Identifying these bacteria helps doctors select appropriate antibiotics, improving infection control and reducing the risk of antibiotic resistance. This test is particularly important for infections that may require broad-spectrum antibiotics.

Short name

Beta-Lactamase Screening (Cefoxitin Disk Test)

Frequently asked questions

What does a positive result mean?
A positive result means your bacteria likely produce beta-lactamase, which can break down cefoxitin and possibly other beta-lactam antibiotics. Your doctor will review the result with you and may adjust your antibiotic treatment accordingly.
How long does it take to get results?
Results are typically available within 24 to 48 hours, depending on the laboratory’s processing time. Your healthcare provider will contact you once the results are ready.
Can I take antibiotics before this test?
Yes, you may take your prescribed antibiotics before the test, but it is important to inform your doctor beforehand. Stopping antibiotics abruptly could affect the test results, so follow your doctor’s 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