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Feline IgG Subclass Measurement (Serum)

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

This test measures the levels of different subclasses of Immunoglobulin G (IgG), a key antibody protein in your cat’s immune system. IgG subclasses help fight infections and support long-term immunity.

Quick summary

["IgG subclasses are important for immune function and can help identify immune system health or deficiencies."]

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

Key facts at a glance

LOINC
110031-2
Short code
A felis IgG Msmt Ser
Synonyms
A felis IgG Msmt Ser
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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 Does This Test Measure?

IgG is divided into five subclasses (IgG1, IgG2, IgG3, IgG4, and IgG5 in felines), each with distinct roles in immunity. This test evaluates the concentration of these subclasses in your cat’s blood serum, often measured using immunoassay methods. The results can help assess immune response, detect immune disorders, or monitor treatment effectiveness.

Why Might This Test Be Ordered?

Veterinarians may recommend this test if your cat shows signs of weakened immunity, recurrent infections, autoimmune diseases, or if they’re receiving immunosuppressive therapy. It can also be part of a broader immune evaluation, especially in cats with chronic illnesses or those at higher risk for infections.

Sample Collection and Preparation

A blood sample is drawn from your cat, typically from a vein in the leg or ear. The blood is processed to separate serum (the liquid part after clotting), which is then analyzed for IgG subclass levels. This process is usually quick and painless, with minimal discomfort for your cat.

What Are Common Reference Ranges?

Reference ranges for feline IgG subclass levels can vary by lab and may not be widely standardized. Your veterinarian will interpret results in the context of your cat’s overall health, age, and medical history. Abnormal findings may require further testing or specialized evaluation.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

IgG Subclass Levels (Serum)

Frequently asked questions

How Might Results Affect My Cat’s Care?
If IgG subclass levels are low, it may indicate an immune deficiency or compromised immune response, potentially due to genetic factors, infections, or treatments like chemotherapy. Elevated levels in certain subclasses might suggest an overactive immune response or inflammation. Your veterinarian will discuss findings with you and recommend next steps, such as additional testing or adjustments to treatment plans.
What Are the Possible Causes of Abnormal Results?
Low IgG subclass levels could be linked to congenital immune disorders, chronic infections, malnutrition, or medications that suppress immunity. High levels might be seen in conditions like autoimmune diseases or severe inflammatory responses. Other factors, such as aging or underlying health conditions, can also influence results.
How Often Should This Test Be Done?
The frequency of testing depends on your cat’s health status. If your cat has a known immune disorder, your vet may recommend periodic monitoring. For healthy cats or those undergoing treatment, testing might be less frequent unless symptoms or lab results suggest changes in immune function.
  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