: Corynebacterium diphtheriae Antibody, Serum
: This test looks for antibodies in your blood that your body makes against Corynebacterium diphtheriae, the bacterium that causes diphtheria. It can help show whether you have been exposed to the bacteria or have responded to vaccination.
[": A Corynebacterium diphtheriae antibody test measures your immune response to the bacterium that causes diphtheria."]
Key facts at a glance
- LOINC
- 47298-5
- Short code
- DIPHAB
- Synonyms
- C diphtheriae Ab 2:1 Ser-Rto
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST) or red-top tube without anticoagulant
- Units
- N/A
- Ref low
- 0.8
- Ref high
- 1.2
- Critical range
- — – 2 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- Enzyme-linked immunosorbent assay (ELISA)
- CPT
- 86317
- SNOMED
- 313260003
- Specimen volume
- 1-2 mL of serum
- Stability
- Serum stable for 7 days at 2-8°C; for extended storage, freeze at -20°C or below for up to 30 days. Avoid repeated freeze-thaw cycles.
- Hemolysis max
- 100
- Lipemia max
- 100
- Icterus max
- 50
- TAT
- 24–72 hours
- Order
- routine
: What This Test Measures
: The test measures antibodies in a blood (serum) sample that bind to Corynebacterium diphtheriae. Antibodies are proteins your immune system makes after exposure to a germ or after vaccination. The result reflects your immune response rather than detecting the bacteria directly.
: Why It May Be Ordered
: Your clinician may order this test to check whether you have antibodies against diphtheria, for example after possible exposure or to assess immune response. It is usually interpreted alongside your vaccination history, symptoms, and other tests.
: How the Sample Is Collected
: A healthcare professional collects a small blood sample, typically from a vein in your arm. The sample is processed to separate serum, and the antibody level is measured in a laboratory.
: What the Results Can Mean
: Results are generally reported as detectable or not detectable, or as a measured level, depending on the laboratory. A positive or detectable result suggests some immune response to the bacterium, while a negative result may mean no detectable antibodies. Your clinician will interpret the result in the context of your history and other findings; specific reference ranges vary by laboratory.
Reference range
Ratio interpretation: <1.0 = no significant change between acute and convalescent specimens; 1.0-1.5 = equivocal/borderline change; >1.5 = significant rise in antibody titer suggestive of recent Corynebacterium diphtheriae infection or recent vaccination. A four-fold or greater rise in titer between paired specimens is considered diagnostic of recent infection.N/A
No fasting required. The first specimen (acute) should be collected as soon as possible after onset of symptoms, ideally within the first 7 days. The second specimen (convalescent) should be collected 14-28 days after the first specimen. Document the collection date of both specimens clearly on the test requisition. Patients should be informed that this test requires two blood draws for meaningful interpretation.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
: Antibody testing for Corynebacterium diphtheriae can support assessment of immune status or past exposure, but it does not by itself diagnose active diphtheria. Diagnosis of diphtheria relies on clinical evaluation and direct detection of the organism, such as by culture. Results should always be interpreted by a healthcare professional alongside vaccination history and symptoms.
Short name
: C. diphtheriae Ab
Frequently asked questions
: Does a positive result mean I have diphtheria?
: Do I need to fast before this test?
: Can vaccination affect my result?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
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.
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 15, 2026. · Read our editorial policy