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Beta-2 Glycoprotein I Antibody IgG

Measures IgG antibodies against beta-2 glycoprotein I, a blood protein. It is one of the tests used when a clinician is looking into antiphospholipid syndrome (APS).

AI-verified against cited sources. Awaiting expert reviewAlso called aβ2GPI IgG, B2GPI IgG, B2GP1 IgGLOINC 44448-9

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What it is

Beta-2 glycoprotein I is a protein in your blood. Many antiphospholipid antibodies actually attach to this protein. In some people the immune system makes IgG antibodies against it. This test measures how much of that antibody is in your serum or plasma. Results come in lab-specific units, and each lab sets its own cutoffs. It is usually done together with anticardiolipin antibodies and a lupus anticoagulant test.

Why it matters

Antibodies that stay positive over time are one of the lab findings used to classify antiphospholipid syndrome (APS). APS is linked to blood clots and certain pregnancy complications. A clinician reads this result with your history of clots or pregnancy problems and the other antiphospholipid tests. One positive result is not enough on its own. These antibodies can appear for a short time, for example after an infection.

If it’s high

A positive result means IgG antibodies to beta-2 glycoprotein I were found. Higher levels carry more weight than low ones. A result that stays positive on a repeat test at least 12 weeks later matters most. Low-level positives are read cautiously, especially when the other antiphospholipid tests are negative. Your clinician will combine the result with your symptoms, history and other tests.

Common causes

  • A low-level result in a person with no known disease
  • A short-lived rise after an infection
  • Some medicines
  • Other autoimmune conditions, especially lupus
  • Antiphospholipid syndrome, when the result stays positive and fits your history

What can help

  • Ask your clinician whether to repeat the test after at least 12 weeks to see if the result persists
  • Ask how this result fits with your lupus anticoagulant and anticardiolipin results
  • Ask which symptoms, such as a swollen, painful leg or sudden shortness of breath, should send you for urgent care

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

For adults: 0–15 U/mL. Source: Mayo Clinic Laboratories.

Mayo Clinic Laboratories ELISA categories (SGU); the 40 and 80 cutoffs match the 2023 ACR/EULAR moderate and high thresholds

  • Negativebelow 15 U/mL
  • Weakly positive15 to under 40 U/mL
  • Positive (moderate level)40 to under 80 U/mL
  • Strongly positive (high level)80 and above U/mL

What can affect your result

  • The assay and its units: ELISA and automated immunoassays give different numbers for the same blood
  • Infections, which can cause short-lived antibodies
  • How long the result lasts: staying positive on a repeat test at least 12 weeks later matters
  • Blood-thinning medicine does not change this type of test, according to Mayo Clinic Laboratories
  • Different assays (ELISA, fluorescence immunoassay, chemiluminescent) report different units and cutoffs, so results from different labs are not directly comparable.
  • Infections can cause antiphospholipid antibodies that come and go, which is why a positive result is usually repeated after at least 12 weeks.
  • Mayo Clinic Laboratories rejects heat-treated, grossly hemolyzed and grossly lipemic samples. Quest also rejects gross hemolysis and gross lipemia.
  • The sample type depends on the lab. Quest prefers platelet-poor plasma from a sodium citrate (light-blue) tube and accepts serum, while Mayo, Labcorp and ARUP use serum.

Antibody levels can change over weeks to months. What matters most is whether the result stays positive when it is repeated at least 12 weeks later.

When to talk to a clinician

Call your local emergency number for sudden chest pain, trouble breathing, sudden weakness, trouble speaking or seeing, or a painful, swollen leg, whatever your antibody result. These can be signs of a blood clot. If you are pregnant or planning pregnancy and an antiphospholipid test is positive, talk with your clinician early.

Questions you could ask

  • Which assay and units did my lab use, and what is its cutoff?
  • Should this test be repeated after 12 weeks?
  • How does this result fit with my lupus anticoagulant and anticardiolipin results?
  • Do my history and symptoms mean I need other tests?

Questions people ask

Why does my lab report different units and ranges than another lab?

Each lab uses its own assay, and each assay has its own scale. One lab may print SGU and another EliA U/mL. A number from one lab cannot be compared directly with a number from another. Use the range printed on your own report, and ask your lab which assay it used.

Why would my clinician repeat this test after 12 weeks?

Antibodies can appear for a short time, for example after an infection. For antiphospholipid syndrome, the antibodies need to be found again at least 12 weeks later.

Do blood thinners change this result?

Not for this kind of test. Mayo Clinic Laboratories states that ELISA and other solid-phase immunoassays are not affected by anticoagulant treatment. Ask your clinician about how treatment affects other antiphospholipid tests.

Show the science and sources

For clinicians and researchers

Anti-β2GPI IgG is one of the laboratory criteria for antiphospholipid syndrome, alongside lupus anticoagulant and anticardiolipin IgG and IgM. The 2006 Sydney criteria count anti-β2GPI IgG or IgM above the 99th percentile when it is present on two or more occasions at least 12 weeks apart. The 2023 ACR/EULAR classification criteria limit aCL and aβ2GPI to ELISA and use fixed thresholds of 40 units (moderate) and 80 units (high) in place of the 99th percentile. The 2025 ISTH SSC guidance notes that classification criteria are stricter than routine laboratory practice, where other platforms and semiquantitative reporting are widely used. Mayo's ELISA reports SGU: below 15.0 negative, 15.0-39.9 weakly positive, 40.0-79.9 positive and 80.0 or more strongly positive. Labcorp uses the Thermo Fisher EliA fluorescence enzyme immunoassay with a 0.0-16.2 EliA U/mL interval. ARUP uses a semi-quantitative ELISA and reports 20 or less SGU as negative. Mayo and ARUP report LOINC 44448-9, and Labcorp reports 16135-6. Results from different commercial immunoassays can disagree, and antibodies made in response to infection cannot always be told apart from those in APS. Isolated low-level positivity carries limited weight. Double or triple positivity with lupus anticoagulant and aCL is linked to higher thrombotic risk (Labcorp test notes).

LOINC 44448-9 (primary), 16135-6, 43914-1. Specimen: serum-or-plasma.

Sources

  1. Beta-2 Glycoprotein 1 Antibodies, IgG, Serum (test GB2GP), Mayo Clinic Laboratories
  2. β2-Glycoprotein 1 Antibodies, IgG (test 163882), Labcorp
  3. β2 Glycoprotein 1 Antibodies (test menu resource), Labcorp
  4. Beta-2-Glycoprotein I Antibody (IgG) (test code 36554), Quest Diagnostics
  5. 2023 ACR/EULAR antiphospholipid syndrome classification criteria, Annals of the Rheumatic Diseases (ACR/EULAR) (2023)
  6. An update on laboratory detection and interpretation of antiphospholipid antibodies for diagnosis of antiphospholipid syndrome: guidance from the ISTH-SSC Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibodies, Journal of Thrombosis and Haemostasis (ISTH) (2025)
  7. International consensus statement on an update of the classification criteria for definite antiphospholipid syndrome (APS), Journal of Thrombosis and Haemostasis (2006)
  8. Beta-2 Glycoprotein 1 Antibodies, IgG and IgM (test 0050321), ARUP Laboratories
  9. LOINC codes and long common names verified with the NLM Clinical Tables LOINC search, U.S. National Library of Medicine

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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