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C. difficile toxin A and B quantitative measurement (serum/plasma)

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

This test detects the presence of toxins produced by *Clostridium difficile*, a harmful bacteria that can cause severe diarrhea and intestinal inflammation.

Quick summary

["Helps diagnose *Clostridium difficile* infection (CDI) by measuring toxins in your blood or body fluids."]

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

Key facts at a glance

LOINC
100909-1
Short code
C sakazakii Ql Cult
Synonyms
C sakazakii Ql Cult
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
organism-specific-culture
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

Why This Test Matters

CDI is a common cause of antibiotic-related diarrhea. Toxins from *C. difficile* damage the intestines, leading to symptoms like severe watery diarrhea, abdominal pain, and fever. This test helps confirm the infection before starting treatment.

How the Test Works

Blood or body fluid samples are tested for specific toxins (A and B) using a sensitive immunoassay method. The test detects these toxins even if the bacteria are not growing in the lab.

What to Expect Before the Test

No special preparation is needed. You may have a simple blood draw or a sample collected from another body fluid (e.g., stool may be used in some cases, but this test specifically measures toxins in blood/plasma).

Possible Results and Next Steps

A positive result means toxins are present, strongly suggesting CDI. A negative result means no toxins were detected, but other causes of diarrhea may still need investigation. Your doctor will guide you on next steps, such as antibiotics or further testing.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

C. diff Toxin A/B Level

Frequently asked questions

What symptoms might trigger this test?
This test is often ordered if you have unexplained severe diarrhea, especially after recent antibiotic use, or if you’re at higher risk for CDI (e.g., elderly, hospitalized, or immunocompromised).
Could this test show false positives or negatives?
Yes, rare conditions or other infections may sometimes cause false positives. Conversely, some people with CDI may test negative if the toxins are not actively present in the sample. Your doctor will review your symptoms and test results together.
How long does it take to get results?
Results are typically available within 24 to 48 hours, depending on lab processing times. Follow-up with your healthcare provider to discuss next steps.
  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