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Oxacillin Minimum Inhibitory Concentration (MIC) Test for Penicillin-Resistant Bacteria (Plasma/Serum)

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

This test measures how much oxacillin a blood sample can inhibit bacterial growth, helping determine if bacteria are resistant to penicillin-based antibiotics.

Quick summary

["Assists doctors in choosing the best antibiotic treatment for infections caused by penicillin-resistant bacteria."]

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

Key facts at a glance

LOINC
73228-9
Short code
Oxacillin ind plt IgM SerPl Ql FC
Synonyms
Oxacillin ind plt IgM SerPl Ql FC
Category
hematology
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
flow-cytometry
CPT
82784
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

What This Test Measures

The test evaluates the lowest concentration of oxacillin needed to stop bacterial growth. This is done by exposing bacteria to different oxacillin levels in your plasma or serum. If bacteria grow despite high oxacillin levels, it suggests resistance to penicillin.

Why It’s Done

Your doctor may order this test if you have an infection that doesn’t respond to standard penicillin antibiotics, or if you’ve been prescribed a penicillin-based drug. It helps identify whether the bacteria causing your infection are resistant to these medications.

How the Test Works

A small sample of your plasma or serum is mixed with oxacillin and bacteria. The sample is then incubated, and the growth of bacteria is observed. The concentration of oxacillin that stops bacterial growth is recorded as the MIC value.

What to Expect Before the Test

No special preparation is needed. You may have a blood draw at a clinic or lab, similar to other blood tests. If you’re on antibiotics, inform your healthcare provider before the test.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Oxacillin MIC

Frequently asked questions

Why is this test important?
This test is critical for guiding antibiotic treatment. High MIC values indicate penicillin-resistant bacteria, which may require alternative antibiotics. It helps prevent unnecessary antibiotic use and reduces the risk of antibiotic resistance in bacteria.
How does this test differ from a standard blood culture?
A standard blood culture identifies the bacteria causing an infection but doesn’t directly measure antibiotic resistance. The oxacillin MIC test specifically assesses how resistant the bacteria are to oxacillin, providing more targeted treatment information.
What if my test results show resistance?
If your test shows resistance to oxacillin, your doctor may switch you to a different antibiotic that is effective against penicillin-resistant bacteria. Follow their instructions carefully to ensure proper treatment and avoid complications.
  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