A quarter of blood donors in five states carry the antibody, and almost none have the allergy

Alpha-gal syndrome (AGS) is an allergy to mammalian meat — pork, beef,
lamb — and to dairy and by-products. **Most cases result from lone star tick
bites.** In 2022, up to 450,000 people in the United States were estimated
to be affected.

It is diagnosed by **alpha-gal immunoglobulin E (IgE) testing together with a
clinical evaluation**. And there is a gap between those two things that this
study measures.

The finding

From 3,000 residual blood donor samples collected during 2024–2025 across
10 states, the estimated alpha-gal IgE seroprevalence was **24.0% in the
five states with the highest seroprevalence** — **Arkansas, Kentucky,
Missouri, Tennessee and Virginia**.

Roughly one blood donor in four, in those states, carries the antibody.

Why that is not one in four with the allergy

People can have alpha-gal IgE antibodies and not have alpha-gal syndrome.
The antibody records an exposure; the syndrome is a clinical illness. Since
only a small minority of seropositive people have AGS, a 24% seroprevalence
does not mean 24% of people in Arkansas cannot eat beef.

The consequence is a testing rule:

• **Health care providers should only test patients with clinically compatible
  symptoms.** Testing someone without symptoms in a high-prevalence state has
  a good chance of returning a positive that means nothing for them.
• Public health surveillance should include clinical criteria, not
  serology alone — otherwise the case count measures tick exposure rather than
  disease.

This is a general problem with any sensitive test used in a population where
the marker is common and the disease is not, and alpha-gal in the American
South is an unusually clean example of it.

*Source: Saunders EF, Taylor ML, Jones ES, et al. Alpha-gal Immunoglobulin E
Seroprevalence Among Blood Donors — 10 States, 2024–2025. MMWR, Centers for
Disease Control and Prevention.*