Skip to content

Beta-lactam Resistance Detection in Blood (Probe Test) – DNA-Based

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

This test checks for genetic markers that may indicate resistance to certain antibiotics, including beta-lactams, in your blood sample. It helps healthcare providers determine if a specific antibiotic will be effective against any bacteria present.

Quick summary

["This test helps guide antibiotic treatment by identifying potential bacterial resistance before starting therapy."]

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

Key facts at a glance

LOINC
105784-3
Short code
BLANDM
Synonyms
Bac b-lactam res NDM Ct Bld +NAA prb
Category
chemistry
Sample
whole-blood
Container
Positive blood culture bottle (aerobic or anaerobic) - typically BacT/ALERT, BACTEC, or equivalent continuously monitored blood culture system bottle
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
0–120 years
Method
probe-amp-tar
CPT
87150
SNOMED
441829004
Specimen volume
Positive blood culture broth; aliquot of 0.5-1.5 mL from positive blood culture bottle transferred to sterile tube for NAA testing
Stability
Stable at 2-8°C for up to 24 hours; frozen at -80°C acceptable for longer storage. Process from positive blood culture broth as soon as possible after signaling positive.
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
1–4 hours
Order
routine

What This Test Measures

The test detects specific DNA sequences (probes) linked to resistance genes for beta-lactam antibiotics, such as penicillin or cephalosporins. These genes can be carried by bacteria in your bloodstream. The presence of these sequences suggests the bacteria may not respond to these antibiotics.

Why It’s Done

Your doctor may order this test if you have an infection suspected to be caused by bacteria, especially if you’ve been prescribed a beta-lactam antibiotic or if you’ve had previous infections that didn’t improve with these medications. It helps ensure the right antibiotic is chosen for your treatment.

How the Test Works

A small sample of your blood is taken and analyzed using molecular techniques (like polymerase chain reaction, or PCR). The test looks for genetic material (DNA) that matches known resistance markers. If these markers are found, it indicates the bacteria may be resistant to certain antibiotics.

Sample Collection and Preparation

Blood is drawn from a vein, typically in your arm. The sample is processed in a lab to extract DNA, which is then tested for resistance markers. This process is usually quick and painless after the initial blood draw.

Reference range

Negative for blaNDM resistance gene. Cycle threshold (Ct) values are reported quantitatively; lower Ct values indicate higher bacterial load.N/A

Specimen: whole-blood

No patient preparation required. Blood culture bottles should be collected prior to initiation of antimicrobial therapy when possible. Standard aseptic technique for blood culture collection is essential to prevent contamination.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

This test is crucial for managing infections by helping doctors select the most effective antibiotic. Identifying resistance early can prevent unnecessary antibiotic use, reduce the risk of antibiotic-resistant infections, and improve treatment outcomes. It’s particularly important in cases of severe or recurrent infections where antibiotic choices are limited.

Short name

Beta-lactam Resistance Probe

Frequently asked questions

What does a positive result mean?
A positive result means that the test detected genetic markers associated with resistance to beta-lactam antibiotics in your blood. This suggests that the bacteria causing your infection may not respond to these antibiotics. Your doctor will use this information to adjust your treatment plan, possibly switching to a different antibiotic that is more effective against resistant bacteria.
What does a negative result mean?
A negative result means that the test did not detect resistance markers for beta-lactam antibiotics in your blood. This does not guarantee that the bacteria are sensitive to these antibiotics, but it suggests that they may be more likely to respond to treatment with beta-lactam drugs. Your doctor will still consider other factors, such as the type of infection and your medical history, when deciding on treatment.
How soon will I get my results?
Results from this test are typically available within a few days to a week, depending on the lab’s processing time. Your doctor will contact you with the results and discuss them in detail, including any changes to your treatment plan if needed.
  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