What Do My Test Results Mean?
Doctors diagnose alpha-gal syndrome through a combination of clinical history and blood tests and sometimes additional tests, including intradermal tests and food challenges. This page is just about the blood tests and how to interpret them. For more general information about diagnosis, see Diagnosis of Alpha-gal Syndrome.
Note that there is more than one red meat allergy, including:
1) Primary meat allergy is an allergy to proteins in red meat. Primary meat allergy is rare and more common in children than adults.
2) Alpha-gal syndrome is an allergy to the sugar galactose-alpha-1,3-galactose (alpha-gal) in red meat and other parts of mammals. AGS is the most common red meat allergy.
3) Pork-cat syndrome makes you allergic to pork.
Your lab report may include some or all of the following test results:
- This is a measure of your galactose-alpha-1,3-galactose (or alpha-gal for short) specific IgE antibodies.
Pork IgE and Beef IgE
- These are measures of your IgE antibodies to the proteins in beef and pork.
- The samples used to perform these tests may contain both proteins and alpha-gal.
- This is a measure of all your IgE antibodies to all allergens, not just to one specific allergen.
What do the results of these tests mean?
You need to ask your doctor what the numbers in your lab report mean. We are not qualified to interpret them for you. However, the following guide may help you talk to your doctor about your results.
Galactose-alpha-1,3-galactose IgE and Total IgE
- At the time this is being written, antibody levels > 0.10 kU/L are typically considered a positive test result.(1)
- Antibody levels >2 IU/ml or >2% of total IgE make the diagnosis of alpha-gal syndrome very likely. (2)
- Physicians at UVA recently saw a case with a convincing history whose total serum IgE was 6.0 IU/ml and alpha-gal IgE was 0.8 IU/ml. Thus, although the sIgE was < 1.0 IU/mL it was nonetheless > 10% of the total IgE. (2)
- As with any allergy, false positives, and possibly subclinical positives, occur. This means that some people who test positive for alpha-gal IgE do not seem to exhibit symptoms after eating red meat. As reactivity to alpha-gal appears to occur on a spectrum, a portion of these people may react to some medications or medical products containing alpha-gal (3) and/or experience symptoms after eating mammalian organs, which contain more alpha-gal than mammalian muscle. (4)
- False positives are more common with people whose alpha-gal IgE levels are <2 IU/ml and <2% of total IgE
- As with any allergy, false negatives also occur, although they are less common. Anecdotal reports from people with AGS seem to suggest that a not insignificant number of people who are initially seropositive for alpha-gal IgE eventually revert to seronegative but continue to experience reactions.
Pork IgE and Beef Ig
If you test positive for pork and/or beef IgE it may mean:
- You are allergic to proteins in pork and/or beef. This is called “primary meat allergy.” It’s a different allergy than alpha-gal syndrome, but both make you allergic to red meat.
- You are not allergic to proteins in pork or beef. You have alpha-gal syndrome. You tested positive because the test samples contain alpha-gal in addition to proteins. This is very common, especially with the beef test.
- Some people who test negative for alpha-gal and beef IgE, but positive for pork IgE, may have pork-cat syndrome. (5)
See below two sets of test results of a real patient. Note that AGS cannot be diagnosed by means of blood tests alone. Clinical history is an important component of diagnosing AGS.
The patient has a clinical history of delayed allergic reactions to beef, pork, dairy, gelatin, dairy, mammalian byproducts in both food and medications, and carrageenan. These reactions include hives, angioedema, anaphylaxis, and abdominal pain occurring 1-10 hours after ingestion
How to interpret these results:
1. The elevated galactose-α-1,3-galactose (alpha-gal) IgE levels and the ratio of galactose-α-1,3-galactose (alpha-gal) IgE to total IgE in conjunction with the patient’s clinical history suggest that the patient has alpha-gal syndrome.
2. The elevated pork and beef IgE do not mean that the patient is allergic to beef and pork proteins. Most likely, alpha-gal in the beef and pork samples used for the test produced the positive results. This is common. Since the patient tests positive for alpha-gal IgE and has delayed reactions after ingesting mammalian meat, these test results don’t have much meaning. Regardless of whether they tested positive or negative for beef and pork protein IgE, they are allergic to alpha-gal in beef and pork.
3. The negative result for porcine gelatin means that the patient is not allergic to the protein in porcine gelatin. However, since the patient tests positive for alpha-gal, which is also in gelatin, they may also react to gelatin. Studies show that patients who are allergic to alpha-gal may have anaphylactic reactions to both ingested and parenterally administered gelatin.
What is this patient allergic to?
1. This patient is not allergic to proteins in porcine gelatin and likely is also not allergic to any proteins in meat.
2. This patient is allergic to galactose-α-1,3-galactose (alpha-gal) which is found in all mammalian cells, tissues, and fluids including all mammalian meats, dairy, and gelatin.
Does my galactose-alpha-1,3-galactose (alpha-gal) IgE level tell me how reactive I will be to alpha-gal?
No. This number does not tell you how reactive you will be to foods, drugs, or other products with alpha-gal in them. It is only useful for predicting whether you will react to them at all.
- Some people with high levels of alpha-gal IgE are not very reactive to it.
- Some people with low levels of alpha-gal IgE are very reactive to it.
- Researchers are studying whether the ratio of alpha-gal IgE/total IgE is correlated with how reactive to alpha-gal people are, but the results of this research have not yet been published.
2. Platts-Mills, T. A., et al. (2019). “Diagnosis and management of patients with the alpha-Gal syndrome.” J Allergy Clin Immunol Pract.
3. Chung, C. H., et al. (2008). Cetuximab-Induced Anaphylaxis and IgE Specific for Galactose-α-1,3-Galactose. N Engl J Med 2008; 358:1109-1117
4. Fischer, J. and T. Biedermann (2016). “Delayed immediate-type hypersensitivity to red meat and innards: current insights into a novel disease entity.” Journal Der Deutschen Dermatologischen Gesellschaft 14(1): 38-43.
5. Posthumus, J. et al. (2013). “Initial Description of Pork-Cat Syndrome in the United States ” The Journal of allergy and clinical immunology vol. 131,3 : 923-5.
6. McGintee, E. (2015). “Meat Allergy Triggered by a Tick Bite with Erin McGintee, MD.” Video-taped lecture. Retrieved from https://youtu.be/hj96Vvr1WhQ.