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Abstract Number: 2455

Establishment of Standardized International Units for IgG Anti-β2glycoprotein Antibody Measurement

Rohan Willis1, Claudia Grossi2, Gabriella Lakos3, Pier Luigi Meroni4, Maria Borghi2, Luis R. Lopez5, Corina Dima6, Marius C. Teodorescu7, Nicholas Ozarka7, Matthias Kast8, Nina Olschowka8, Alfredo Villarreal9, Maria Crisostomo10, Mike Watkins9, Wendy Vandam11, Tony Prestigiacomo11, Josep Puig12, Kerrie Jaskal13, Roger Walker10, Sarah Paul9, T. Buckner14, Fernando S. Cavalcanti12 and Silvia S. Pierangeli15, 1Rheumatolgoy/Dept Int Med, University of Texas Medical Branch, Galveston, TX, 2Lab of immunology, IRCCS Istituto Auxologico Italiano, Milano, Italy, 3Research, INOVA Diagnostics, San Diego, CA, 4Chair and Division of Rheumatology, Gaetano Pini Institute, University of Milan, Milan, Italy, 5Corgenix Inc, Broomfield, CO, 6Microbiology, Theratest Laboratories Inc, Lombard, IL, 7Microbiology, TheraTest Laboratories Inc, Lombard, IL, 8Phadia Thermofisher, Freiburg, MN, Germany, 9BioPlex Division, Bio-Rad Laboratories, Benicia, CA, 10Bio-rad Laboriatories, In, Bio-Rad Laboratories, Hercules, CA, 11Bio-Rad Laboratories, Hercules, CA, 12Biokit, Barcelona, Spain, 13Instrumentation Laboratories, Bedford, MA, 14Corgenix, Broomfield, CO, 15Rheumatology/Dept Int Med, University of Texas Medical Branch, Galveston, TX

Meeting: 2012 ACR/ARHP Annual Meeting

Keywords: Anticardiolipin, antiphospholipid syndrome and autoantibodies

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Session Information

Title: Antiphospholipid Syndrome

Session Type: Abstract Submissions (ACR)

Background/Purpose:   Despite numerous efforts aimed at the standardization of assays for detection of anti-β2Glycoprotein I (aβ2GPI)antibodies, there are still concerns, including the type and source of properly validated calibrant and reference material and the lack of universal units of measurement.  Based on recommendations of an international task force at the 13th Congress on Antiphospholipid Antibodies , a project was started with the goals of establishing a reference preparation (RP) and  international consensus units (IU) for the measurement for IgG aβ2GPI antibodies. 

Methods: Whole IgG fractions were affinity-purified (AP) from sera of 2 primary Antiphospholipid syndrome patients with high IgG ab2GPI levels using a Protein G Sepharose column. Pooled IgG fractions were further AP using an affinity column coupled to β2GPI, and the protein concentration of the AP material was determined using two methods, and a value based on the definition that 1 IU/ml equates to 1µg/ml of AP aβ2GPI, was assigned.  A reference preparation (RP) serum created from sera taken from the 2 original PAPS patients was then assigned an IU value based on repeated testing using original AP material as a calibrator. RP was sent to six commercial companies for testing in their respective kits (eight total) according to an approved protocol to enable evaluation of linearity and unit equivalency, along with a set of 30 samples (APS samples and healthy controls) to allow for commutability studies to be done. Companies (and kits) included INOVA Diagnostics (QUANTA Lite ® β2GPI IgG ELISA, QUANTA Flash ® β2GPI IgG chemiluminescent assay), Bio-Rad Laboratories (BioPlex ® 2200 APLS IgG Kit, Anti-β2Glycoprotein I IgG EIA Test Kit) TheraTest (EL-b2GPI IgG kit), Corgenix (IgG Anti-Beta 2 Glycoprotein I Test Kit), Phadia (EliA ß2-Glycoprotein I IgG on Phadia® 250) and Instrumentation Laboratory (HemosIL® AcuStar anti-β2Glycoprotein-I IgG).

Results: The pooled AP material had a protein concentration of 103.1 µg/ml (OD280nm) and 108.8 µg/ml (Bradford) and was assigned a value of 100 IgG aβ2GPI IU/ml. RP had a value of 270 IgG aβ2GPI IU/ml. The R2  values of the regression lines of the RP for all kits were >0.95. The value of the RP in the various  kit units ranged from 115 to 9993.1. Results of correlations between kits with commutability samples are shown in Table 1 (kit units and international units).

Conclusion: Establishment of equivalency between kit units and IU value of RP was successful. The RP demonstrated excellent linearity and was commutable in the various aβ2GPI IgG assays and is therefore adequate to be used as a reference material. Expressing results in in the new IU instead of arbitrary kit units illustrated the comparability of the results obtained in the different kits.  These studies contribute significantly to the much-needed standardization of aβ2GPI immunoassays.

Table 1. Correlation of commutability sample values among various ab2GPI assays






CORRELATIONS OF COMMUTABILTY SAMPLES IN INTERNATIONAL UNITS

 

IL

AcuStar

INOVA

BIO-FLASH

INOVA

ELISA

Bio-Rad

ELISA

Bio-Rad

BioPlex

Theratest

Corgenix

Phadia






CORRELATIONS OF COMMUTABILITY SAMPLES IN KIT UNITS

IL

AcuStar

 

.996

.961

.940

.990

.978

.966

.950

INOVA

BIO-FLASH

0.996

 

.959

.935

.988

.971

.961

.939

INOVA

ELISA

0.938

0.933

 

.896

.942

.987

.925

.956

BioRad

ELISA

0.972

0.963

0.897

 

.929

.914

.915

.846

Bio-Rad

BioPlex

0.948

0.945

0.810

0.920

 

.960

.963

.933

Theratest

 

0.964

0.958

0.978

0.936

0.891

 

.949

.958

Corgenix

 

0.974

0.968

0.911

0.993

0.907

0.939

 

.905

Phadia

 

0.953

0.944

0.944

0.898

0.878

0.958

0.903

 

For values in table: p<0.001


Disclosure:

R. Willis,
None;

C. Grossi,
None;

G. Lakos,

Inova Diagnostics, Inc.,

3;

P. L. Meroni,
None;

M. Borghi,
None;

L. R. Lopez,

Corgenix,

1;

C. Dima,

Thera test Laboratories,

3;

M. C. Teodorescu,

TheraTest Laboratories,

1;

N. Ozarka,

TheraTest Laboratories,

3;

M. Kast,

Phadia Therfishrer,

3;

N. Olschowka,

Phadia Thermofisher,

3;

A. Villarreal,

BioRad Laboratories,

3;

M. Crisostomo,

BioRad Laboratories,

3;

M. Watkins,

Bio-Rad Laboratories,

3;

W. Vandam,

BioRad Laboratories,

3;

T. Prestigiacomo,

Bio-Rad Laboratories ,

3;

J. Puig,

Biokit ,

3;

K. Jaskal,

Instrumentation Laboratories ,

3;

R. Walker,

Bio-Rad Laboratories ,

3;

S. Paul,

Bio-Rad Laboratories ,

3;

T. Buckner,

Corgenix,

3;

F. S. Cavalcanti,

Biokit,

3;

S. S. Pierangeli,
None.

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