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Bacterial Culture and Antimicrobial Susceptibility Testing (Blood Culture with Antibiotic Probe)

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

This test checks for bacteria in your blood and helps determine which antibiotics could effectively treat any infection found.

Quick summary

["Identifies potential infections and guides antibiotic treatment choices."]

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

Key facts at a glance

LOINC
105780-1
Short code
CTXMRES
Synonyms
blaCTX-M Ct Bld Pos Qn NAA+probe
Category
chemistry
Sample
whole-blood
Container
Positive blood culture bottle (e.g., aerobic and/or anaerobic BacT/ALERT, BACTEC, or equivalent continuously-monitored blood culture system) transferred to a sterile, leak-proof molecular transport tube or tube recommended by the assay manufacturer
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
0–120 years
Method
probe-amp-tar
CPT
87801 (infectious agent detection by nucleic acid, amplified probe technique, each organism); additional CPT codes may apply for multiplex panel organisms (e.g., 87506, 87641)
SNOMED
122450008 | Microbial resistance gene detected (finding)
Specimen volume
1-2 mL of broth from a positive blood culture bottle, or per assay manufacturer specifications
Stability
Process positive blood culture broth as soon as possible (within 24 hours of positivity signal). If delay is unavoidable, refrigerate at 2-8°C for up to 24-48 hours per assay package insert; do not freeze. Stable at room temperature for up to 2-4 hours.
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
1–8 hours
Order
routine

What This Test Does

A blood sample is taken to detect the presence of bacteria. If bacteria are found, this test uses a specialized probe to assess how different antibiotics might affect them, helping your healthcare provider choose the best treatment.

How the Test Works

The blood sample is processed in a controlled environment where bacterial growth is monitored. If bacteria are detected, antibiotic probes are introduced to measure their susceptibility, often using a colorimetric or fluorescent change to indicate effectiveness.

When You Might Need This Test

This test is typically ordered if you have symptoms of a serious blood infection (sepsis), fever of unknown origin, or other signs of infection that may require targeted antibiotic treatment.

Preparation for the Test

No special preparation is needed. You may have a small needle inserted into a vein (usually in your arm) to draw blood. If you are on antibiotics, let your healthcare provider know before the test.

Reference range

Negative (target gene not detected). Result reported as Cycle Threshold (Ct) value when positive; lower Ct values indicate higher bacterial gene load.N/A

Specimen: whole-blood

No special patient preparation required. Sample collected from positive blood culture bottle; ensure blood culture was obtained prior to initiation of antibiotics when clinically feasible. Avoid collection during active antimicrobial therapy if possible, as it may reduce organism yield.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Blood Culture with Antimicrobial Probe

Frequently asked questions

This test is crucial for diagnosing blood infections and ensuring the correct antibiotic is prescribed, reducing the risk of antibiotic resistance and improving recovery.
Blood cultures with antibiotic probes help confirm infections and guide treatment decisions by identifying the most effective antibiotics for your specific case.
How long does it take to get results from this test?
Results can take several days to a week, depending on bacterial growth and susceptibility testing. Your healthcare provider will discuss the findings with you once they are available.
What if bacteria are found in my blood?
If bacteria are detected, your healthcare provider will work with you to determine the best antibiotic treatment based on the probe results. Follow-up tests or additional blood cultures may be needed to monitor your recovery.
  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