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Escherichia coli (E. coli) bacterial culture with antimicrobial susceptibility testing (serum/plasma specimen)

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

This test checks for the presence of *Escherichia coli* bacteria in your blood and evaluates how well your blood is responding to antibiotics.

Quick summary

["Helps identify infections and guide antibiotic treatment choices."]

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

Key facts at a glance

LOINC
20812-4
Short code
E coli987p TSMI Ql IF
Synonyms
E coli987p TSMI Ql IF
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
0.8
Ref high
1.2
Critical range
— – 5 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
if
CPT
85610
SNOMED
396252006
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 involves growing bacteria from your blood sample to detect *E. coli* and determining if it grows in the presence of common antibiotics. This helps doctors choose the most effective treatment.

Why It’s Ordered

Your doctor may order this test if you have symptoms like fever, chills, or signs of infection (e.g., rapid heartbeat, confusion) that could be caused by a bloodstream infection, including one caused by *E. coli*.

Sample Collection and Preparation

A blood sample is taken from a vein, usually in your arm. The sample is sent to a lab where bacteria are cultured over time to identify *E. coli* and assess antibiotic resistance patterns.

What to Expect Before the Test

No special preparation is needed, but inform your doctor about any recent illnesses, medications, or allergies—especially antibiotics—to avoid misleading results.

Reference range

INR: 0.8-1.2 (warfarin: 2.0-3.0)N/A

Specimen: serum

Inform your healthcare provider if you are taking blood thinners. No special preparation required.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Positive results indicate a *E. coli* infection, which may require immediate medical attention. Antibiotic susceptibility testing helps prevent overuse of broad-spectrum antibiotics by targeting the most effective ones for your specific bacteria.

Short name

E. coli bloodstream infection screening

Frequently asked questions

How long does it take to get results?
Results typically take 2–5 business days, depending on lab processing. Some labs may provide preliminary findings sooner.
What does a positive result mean?
A positive result means *E. coli* was detected in your blood. This could mean you have a bloodstream infection and may need antibiotics tailored to your specific bacteria.
Could I have this test if I’m on antibiotics?
Yes, but results may be affected. Inform your doctor about current medications to avoid misleading interpretations.
  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