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Test Code B2GMG Beta-2 Glycoprotein 1 Antibodies, IgG and IgM, Serum

Useful For

Evaluation of patients with suspected antiphospholipid syndrome by identification of beta-2 GP1 IgG and IgM antibodies

Profile Information

Test ID Reporting Name Available Separately Always Performed
GB2GP Beta 2 GP1 Ab IgG, S Yes Yes
MB2GP Beta 2 GP1 Ab IgM, S Yes Yes

Reporting Name

Beta 2 GP1 Ab, IgM/IgG, S

Specimen Type

Serum


Specimen Required


Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Specimen Volume: 0.5 mL


Specimen Minimum Volume

0.4 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Refrigerated (preferred) 21 days
  Frozen  21 days

Reject Due To

Hemolysis

Mild OK; Gross reject

Lipemia

Mild OK; Gross reject

Icterus

Mild OK; Gross OK

Other

NA

Clinical Information

Beta-2 glycoprotein 1 (beta-2 GP1, also called apolipoprotein H) is a 326-amino acid polypeptide synthesized by hepatocytes, endothelial cells, and trophoblast cells. It contains 5 homologous domains of approximately 60 amino acids each.(1,2) Domain 5, located at the C terminus, contains a hydrophobic core surrounded by 14 positively charged amino acid residues that promote electrostatic interactions with plasma membranes via interactions with negatively charged phospholipids. Complexes of beta-2 GP1 and phospholipids in vivo reveal epitopes that react with natural autoantibodies.(3) Plasma from normal individuals contains low concentrations of IgG autoantibodies to beta-2 GP1 (beta-2 GP1 antibodies) that are of moderate affinity and react with an epitope on the first domain near the N terminus.

 

Pathologic levels of beta-2 GP1 antibodies occur in patients with antiphospholipid syndrome (APS). APS is associated with a variety of clinical symptoms, notably, thrombosis, pregnancy complications, unexplained cutaneous circulatory disturbances (livido reticularis or pyoderma gangrenosum), thrombocytopenia or hemolytic anemia, and nonbacterial thrombotic endocarditis. Beta-2 GP1 antibodies are found with increased frequency in patients with systemic rheumatic diseases, especially systemic lupus erythematosus.

 

Beta-2 GP1 antibodies are detected in the clinical laboratory by different types of assays including immunoassays and functional coagulation assays. Immunoassays for beta-2 GP1 antibodies can be performed using either a composite substrate comprised of beta-2 GP1 plus anionic phospholipid (eg, cardiolipin or phosphatidylserine), or beta-2 GP1 alone. Antibodies detected by immunoassays that utilize composite substrates are commonly referred to as phospholipid or cardiolipin antibodies. Antibodies detected using beta-2 GP1 substrate without phospholipid (so-called direct assays) are referred to simply as beta-2 GP1 antibodies. Some beta-2 GP1 antibodies are capable of inhibiting clot formation in functional coagulation assays that contain low concentrations of phospholipid cofactors. Antibodies detected by functional coagulation assays are commonly referred to as lupus anticoagulants.

 

The diagnosis of APS requires at least 1 clinical criteria and 1 laboratory criteria be met.(5) The clinical criteria include vascular thrombosis (arterial or venous in any organ or tissue) and pregnancy morbidity (unexplained fetal death, premature birth, severe preeclampsia, or placental insufficiency). Other clinical manifestations, including heart valve disease, livedo reticularis, thrombocytopenia, nephropathy, neurological symptoms, are often associated with APS but are not included in the diagnostic criteria. The laboratory criteria for diagnosis of APS are the presence of lupus anticoagulant, the presence of IgG and/or IgM anticardiolipin antibody (>40 GPL, >40 MPL, or >99th percentile), and/or the presence of IgG and/or IgM beta-2 GP1 antibody (>99th percentile). All antibodies must be demonstrated on 2 or more occasions separated by at least 12 weeks. Direct assays for beta-2 GP1 antibodies have been reported to be somewhat more specific (but less sensitive) for disease diagnosis in patients with APS.(4) Anticardiolipin and beta-2 GP1 antibodies of the IgA isotype are not part of the laboratory criteria for APS due to lack of specificity.

Reference Values

<15.0 U/mL (negative)

15.0-39.9 U/mL (weakly positive)

40.0-79.9 U/mL (positive)

≥80.0 U/mL (strongly positive)

Results are expressed in arbitrary units and apply to IgG and IgM values.

Reference values apply to all ages.

Interpretation

Strongly positive results for beta-2 glycoprotein 1 (beta-2 GP1) antibodies (>40 U/mL for IgG and/or IgM) are diagnostic criterion for APS. Lesser levels of beta-2 GP1 antibodies and antibodies of the IgA isotype may occur in patients with clinical signs of antiphospholipid syndrome (APS), but the results are not considered diagnostic. Beta-2 GP1 antibodies must be detected on 2 or more occasions at least 12 weeks apart to fulfill the laboratory diagnostic criteria for APS.

 

Detection of beta-2 GP1 antibodies is not affected by anticoagulant treatment.

Clinical Reference

1. Caronti B, Calderaro C, Alessandri C, et al: Beta2-glycoprotein 1 (beta2-GP1) mRNA is expressed by several cell types involved in anti-phospholipid syndrome-related tissue damage. Clin Exp Immunol 1999;115:214-219

2. Lozier J, Takahashi N, Putnam F: Complete amino acid sequence of human plasma beta-2-glycoprotein 1. Proc Natl Acad Sci USA 1984;81:3640-3644

3. Kra-Oz Z, Lorber M, Shoenfeld Y, Scharff Y: Inhibitor(s) of natural anti-cardiolipin autoantibodies. Clin Exp Immunol 1993;93:265-268

4. Audrain MA, El-Kouri D, Hamidou MA, et al: Value of autoantibodies to beta(2)-glycoprotein 1 in the diagnosis of antiphospholipid syndrome. Rheumatology (Oxford) 2002;41:550-553

5. Wilson WW, Gharavi AE, Koike T, et al: International consensus statement on preliminary classification criteria for definite antiphospholipid syndrome. Arthritis Rheum 1999;42(7):1309-1311

Day(s) and Time(s) Performed

Monday through Saturday; 8 a.m.

Analytic Time

Same day/1 day

Performing Laboratory

Mayo Medical Laboratories in Rochester

CPT Code Information

86146 x 2

LOINC Code Information

Test ID Test Order Name Order LOINC Value
B2GMG Beta 2 GP1 Ab, IgM/IgG, S In Process

 

Result ID Test Result Name Result LOINC Value
GB2GP Beta 2 GP1 Ab IgG, S 44448-9
MB2GP Beta 2 GP1 Ab IgM, S 44449-7

Method Name

Enzyme-Linked Immunosorbent Assay (ELISA)

Forms

If not ordering electronically, complete, print, and send 1 of the following forms with the specimen:

Coagulation Test Request Form (T753) (http://www.mayomedicallaboratories.com/it-mmfiles/coagulation-test-request-form.pdf)

General Request Form (T239) (http://www.mayomedicallaboratories.com/it-mmfiles/general-request-form.pdf)

Secondary ID

62926

Test Classification

This test has been cleared or approved by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.