Food-Specific IgG Blood Tests

IgG blood tests are not currently recommended in clinical practice.

Please listen to the audio recording.

How would you approach this client?

IgG is one of five antibodies. It is our main line of defence against pathogenic microorganisms. The immune system also makes IgG antibodies to food, but the reason is not entirely understood. 

Theory: “IgG + Food Complex” Causes Disease: For many decades, there has been a theory that food-specific IgG forms a complex with its analogous food and deposits in body tissues – leading to inflammation, tissue damage and disease. We will talk about the lack of evidence for this theory in a minute.

Reality: IgG4 is related to food tolerance: As discussed in IgE Food Allergy (Module #3: Above the Water), when anaphylactic patients develop tolerance, their allergen-specific IgE levels drop, and their IgG4 levels increase. IgG4 is one of the four identified subtypes, so there is still much to learn. 

Complementary practitioners are the most common HCPs ordering IgG tests.

  • Blood samples are usually drawn at a lab: In Canada, the big ones are:
  • Rocky Mountain Analytical Lab (Life Labs): The lab is in Calgary, Alberta, but other labs can mail blood samples.
  • Dynacare: sells this test in some provinces, especially Ontario. Dynacare also provides routine, validated tests (e.g., CBCs). Patients and HCP may incorrectly assume that all tests at this lab are valid.
  • Home test (finger prick):  Clients can also order an at-home finger-prick kit to mail back. These companies come and go. Two current ones are Pinner Test and EverylyWell.
  • Labs report different things: Most labs report total IgG, but some measure IgG4 or a combination of IgE & IgG4.
  • Results are reported on a scale: Every company has a different method of reporting results, but it is often a colour scale:

Green (safe foods – eat freely)

Orange (suspect foods – be careful)

Red (bad foods – restrict)  

Evidence is not supportive: Evidence does not support using food-specific IgG testing in clinical practice. Several studies have investigated the value of IgG testing– and there is moderate evidence that it is ineffective. A common argument is, “No research does not mean the test is ineffective.” However, “no evidence” differs from “evidence that it is ineffective.” The companies selling these tests list supportive research, but most are open (no comparison with a blinded comparison group) or have other significant methodological flaws  AD #13 & #14.

Lab procedures are not standardized: The same blood sample sent to different labs will give different results, and the results from the same blood analyzed at the same lab are even more alarming.

Study results cannot be generalized to other labs: Even if a study showed clinical value, those results only apply to the lab where the research was done (since each lab uses different procedures).

Recommendations are not standardized: If three practitioners had the same results, they would likely interpret them differently and give inconsistent clinical recommendations. For example, one practitioner may suggest avoiding red and orange foods, while another may recommend red foods only.

We all have food-specific IgG: Finally, we all have food-specific IgG, so everyone tested will have a list of “no-no” foods. A recent Dynacare advertisement claimed that up to 45% of people have food intolerances. How does a test that is 100% positive find the 45% with food intolerance?

I have two conclusions to the case study, depending on the client’s goals.

Please listen to the audio recordings.