Skip to content

Macrolide Resistance Detection in Blood (Qualitative)

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

This test checks whether certain bacteria in your blood may be resistant to macrolide antibiotics, which are used to treat infections like pneumonia or ear infections.

Quick summary

["Helps determine if your infection may need different treatment options."]

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

Key facts at a glance

LOINC
105810-6
Short code
ERMA-PCR
Synonyms
Bac macrolide res ErmA Ct Bld +
Category
chemistry
Sample
whole-blood
Container
Positive blood culture bottle (aerobic or anaerobic) transferred to a sterile, leak-proof, nucleic acid-stabilizing transport tube or direct-from-bottle PCR reaction vessel per laboratory protocol.
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
≥ 0 years
Method
probe-amp-tar
CPT
87500
SNOMED
122450006
Specimen volume
Approximately 0.5-1 mL of blood culture broth aliquot transferred from a positive flagged blood culture bottle for molecular testing.
Stability
Test should be performed as soon as possible after blood culture flags positive, ideally within 24 hours. If delay is necessary, store blood culture broth at 2-8°C for up to 72 hours. Avoid repeated freeze-thaw cycles.
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
1–8 hours
Order
routine

Why This Test Is Done

Your healthcare provider may order this test if you have symptoms of an infection that could be caused by bacteria that are resistant to macrolides, such as strep throat or community-acquired pneumonia. It’s also used in some hospital settings to guide antibiotic choices for patients with suspected infections.

What to Expect Before the Test

No special preparation is needed. A healthcare professional will draw blood from a vein in your arm, similar to other routine blood tests. The blood sample will be sent to a lab for testing.

What the Test Results Mean

The test result will indicate whether the bacteria in your blood are likely resistant to macrolides (positive result) or not (negative result). A positive result means the bacteria may not respond to macrolide antibiotics, so your doctor may choose a different antibiotic or adjust your treatment plan.

Possible Side Effects or Risks

The blood draw itself carries mild risks, such as bruising, slight pain, or a small bump at the injection site. There are no known side effects from the macrolide resistance testing itself.

Reference range

Negative for ErmA gene (macrolide resistance gene not detected). Cycle threshold (Ct) values are reported when positive; lower Ct values indicate higher bacterial load. No universally established numeric Ct cutoff for clinical decision-making.N/A

Specimen: whole-blood

No special patient preparation required. Testing is performed on a positive blood culture specimen, so sample collection precedes this molecular resistance test. Standard blood culture collection asepsis protocols apply at time of blood draw.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Macrolide Resistance Screen

Frequently asked questions

How can I prepare for this test?
You should avoid taking macrolide antibiotics (like azithromycin or clarithromycin) for at least 24 hours before testing if possible, as this could affect results. Follow your doctor’s instructions.
What if my test result is positive?
A positive result suggests your infection may require a different antibiotic. Your doctor will discuss alternative treatments with you, possibly including broader-spectrum antibiotics or additional testing to identify the exact bacteria causing your infection.
Does this test affect my antibiotic choices permanently?
No, this test provides guidance for your current treatment plan. If your infection improves or worsens, your doctor may repeat testing or adjust medications as 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