What is the difference between IgG and IgG4?

IgG and IgG4 measure different types of reactions within the complement system and it is important to test for them separately.

IgG or immunoglobulin G has 4 different subclasses of antibodies: IgG1, IgG2, IgG3, and IgG4. Many food sensitivity tests only measure IgG total which combines all the subclasses of IgG into one measurement providing an incomplete and sometimes even false picture of an individual's food sensitivities and protocol needs.

To ensure you are preparing protocols for your patients that lead to the best clinical outcomes it is important to test for IgG1-3 and IgG4 separately. Below is a breakdown of why this is important.


IgG1-3 (also known as IgG) are antibodies that can activate the pro-inflammatory complement system (complement cascade) associated with chronic inflammatory conditions. High levels of IgG (class II or higher) overload receptors and drive the inflammatory reaction while low levels of IgG (class 0/I) indicate tolerance.  

IgG testing is the most commonly performed food sensitivity testing and foods that are only high in IgG can often be safely re-introduced after a period of abstinence. 


IgG4 is an antibody that in most people does not activate the complement system, but instead is a “blocking antibody” for IgE. The presence of IgG4 is protective, not inflammatory, as IgG4/IgE binding tends to decrease IgE hypersensitivity (true allergy). If IgG4 is high, testing for IgE reactivity is advised and it may be best to remove the food from the diet permanently.  

 Independent increases in IgG4 only can be associated with certain autoimmune conditions such as:

  • Autoimmune pancreatitis
  • Kidney problems
  • Prostatitis
  • Lymph node inflammation
  • Inflammation of the aorta
  • Eosinophilic esophagitis (EOE) and other problems.


You can learn more about US BioTek's food sensitivity panels at https://www.usbiotek.com/food-sensitivity-testing