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Antibiotic Sensitivity Test: Cefotaxime Breakpoint Detection (Microscopic Observation)

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

This test helps determine whether your bacteria are likely to be resistant to the antibiotic cefotaxime, which is used to treat certain infections. Results guide decisions about treatment options.

Quick summary

["Assists doctors in choosing the most effective antibiotic for your infection by identifying potential resistance patterns."]

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

Key facts at a glance

LOINC
101479-4
Short code
CEFOTAX
Synonyms
Cefotaxime Bld Pos MIC.VOC det
Category
chemistry
Sample
whole-blood
Container
Positive blood culture bottle (aerobic and/or anaerobic) inoculated with whole blood; standard BacT/ALERT, BACTEC, or equivalent blood culture system bottles
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
0–120 years
Method
mic-voc-detection
CPT
87186
SNOMED
363525000
Specimen volume
8-10 mL of whole blood per blood culture bottle (adult); minimum 1-3 mL for pediatric bottles
Stability
Blood culture bottles must be incubated promptly upon collection and continuously monitored. Once flagged positive, perform susceptibility testing as soon as possible; do not exceed 24 hours after positivity alert.
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
12–48 hours
Order
routine

What This Test Measures

This test evaluates the bacteria’s response to cefotaxime by observing growth inhibition under a microscope. A positive result (no visible growth) suggests the bacteria are sensitive to the drug, while a negative result (growth visible) may indicate resistance. This is a qualitative screening, not a precise measurement of antibiotic concentration.

Specimen and Preparation

A sample of your blood is taken and mixed with bacteria from your infection. The mixture is then exposed to cefotaxime and observed for bacterial growth. No special preparation is needed beyond standard blood draw procedures.

How the Test Works

The test uses a qualitative method to detect whether bacteria grow in the presence of cefotaxime. If bacteria survive (visible growth), they may be resistant. If they do not grow (no visible growth), they are likely sensitive. This is a visual assessment, not a numerical measurement.

When You Might Need This Test

This test is typically ordered when your doctor suspects bacterial infections that may require cefotaxime treatment, such as certain types of pneumonia, urinary tract infections, or meningitis. It helps ensure the antibiotic chosen will be effective against your specific infection.

Reference range

Interpretive categories per CLSI breakpoints: Susceptible (S) ≤ 1 µg/mL, Intermediate (I) 2 µg/mL, Resistant (R) ≥ 4 µg/mL for Enterobacterales; refer to current CLSI M100 or EUCAST guidelines for specific organism breakpointsN/A

Specimen: whole-blood

No fasting required. Specimen should be collected prior to initiation of antimicrobial therapy whenever possible. If patient is already on antibiotics, note medication and timing on requisition.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Cefotaxime MIC Screening (Qualitative)

Frequently asked questions

Why might my doctor order this test?
Your doctor may order this test to confirm whether your infection is caused by bacteria that are likely to respond to cefotaxime. This helps avoid unnecessary antibiotic use if the bacteria are resistant, reducing the risk of antibiotic resistance in your body or community.
How long will I need to wait for results?
Results are usually available within 24 to 48 hours, depending on lab processing times. Your doctor will discuss the findings with you during your follow-up visit.
What if the test shows resistance to cefotaxime?
If the test indicates resistance, your doctor may switch you to a different antibiotic that is more effective against your infection. This helps prevent the bacteria from becoming resistant to multiple treatments.
  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