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Coxsackievirus A21 Antibody Test, Complement Fixation

Published: August 9, 2026Updated: August 10, 2026

This blood test measures antibodies against Coxsackievirus A21 in your body using the complement fixation method. It helps your doctor determine whether you have a current or past infection with this virus, which can cause symptoms such as sore throat, fever, blisters in the mouth or on the hands and feet, and in some cases more serious illness involving the heart or the protective covering of the brain and spinal cord.

Quick summary

{"Detects immune response to Coxsackievirus A21 infection","Helps diagnose viral infections affecting the heart, skin, and nervous system","Sample is collected from blood (serum)","Results indicate past or recent infection","Often used when heart-related symptoms suspect viral cause"}

Medically reviewed by WellAlly Editorial TeamLast reviewed August 10, 2026Editorial policy

Key facts at a glance

LOINC
6956-7
Short code
COXA21
Synonyms
CV A21 Ab Titr Ser CF
Category
cardiac
Sample
serum
Container
Serum separator tube (SST) or plain red top tube
Units
N/A
Ref low
8
Ref high
32
Fasting
false
Population
adult
Sex
all
Age range
≥ 0 years
Method
comp-fix
CPT
86658
SNOMED
371949004
Specimen volume
1.0 mL serum minimum
Stability
Room temperature: 8 hours; Refrigerated (2-8°C): 72 hours; Frozen (-20°C or below): 30 days
Hemolysis max
50
Lipemia max
300
Icterus max
20
TAT
72–168 hours
Order
routine

What is this test?

The Coxsackievirus A21 Antibody Test is a blood test that detects antibodies your immune system produces in response to Coxsackievirus A21 infection. The test uses a method called complement fixation, which measures whether your blood contains specific antibodies that can bind to the virus and activate the complement system - part of your immune defense.

What is Coxsackievirus A21?

Coxsackievirus A21 is a type of enterovirus that belongs to the Picornaviridae family. It can cause various illnesses including hand, foot, and mouth disease, herpangina (painful blisters in the throat), aseptic meningitis, and in some cases, myocarditis (heart muscle inflammation) or pericarditis (heart lining inflammation).

How is the test performed?

A healthcare professional will draw a small blood sample from a vein in your arm. The blood is then sent to a laboratory where technicians test the serum (the liquid part of blood) for antibodies against Coxsackievirus A21 using the complement fixation technique.

What do the results mean?

A positive result indicates that you have or have had a Coxsackievirus A21 infection. A negative result means no antibodies were detected, which could mean you have never been infected or the infection was too recent for antibodies to develop. Your doctor will interpret these results along with your symptoms and medical history.

Reference range

Negative: <1:8; Equivocal: 1:8-1:32; Positive: >1:32N/A

Specimen: serum

No special preparation required. Fasting not necessary.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

This test is primarily used to confirm Coxsackievirus A21 infection, especially when patients present with symptoms affecting the heart (myocarditis, pericarditis), nervous system (meningitis), or skin/mucous membranes (hand-foot-mouth disease). It helps differentiate viral causes from other conditions and guides appropriate management. In cardiac patients, identifying a viral trigger can influence treatment decisions and prognosis.

Frequently asked questions

Do I need to fast before this test?
No, fasting is not required for this blood test. You can eat and drink normally before the test.
Is this test painful?
You may feel a brief sting or pinch when the needle is inserted to draw blood. This is generally well tolerated and the discomfort goes away quickly.
How long does it take to get results?
Results are typically available within a few days to a week, depending on the laboratory.
What are the symptoms of Coxsackievirus A21 infection?
Symptoms vary but may include fever, sore throat, blisters in the mouth or on hands and feet, headache, muscle aches, and in more serious cases, chest pain, shortness of breath (suggesting heart involvement), or stiff neck and sensitivity to light (suggesting meningitis).
Is Coxsackievirus A21 contagious?
Yes, Coxsackievirus A21 spreads through close personal contact, respiratory droplets, and contact with contaminated surfaces. Good hygiene practices like frequent handwashing can help prevent spread.
  1. 1
    CDC - EnterovirusesSource
  2. 2
    Mayo Clinic - MyocarditisSource

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 10, 2026. · Read our editorial policy