Background New emerging anti-phospholipid (aPL) assays could improve our ability in diagnosing anti-phospholipid syndrome (APS). However, the availability of aPL assays in routine laboratory practice is limited and present available assays frequently not so efficient.
Objectives To test the performance of a new immunometric assay for prothrombin/phosphatidylserine IgG and IgM complex autoantibodies (aPT/PS) in routinely attending patients (Autoimmunology Unit, University Hospital of Udine, Italy).
Methods The study included 138 consecutive patients (78% female, age 53±15 years; range 18-88) amongst which 83 with systemic lupus erythematosus (SLE), undifferentiated connective tissue diseases (UCTD) or APS. 52 healthy donors (29F/23M, age 37±13 yrs, range 18-65) were enrolled as controls. From the laboratory point of view, there were 108 lupus anticoagulant (LAC) positive patients (70.4% of which anti-cardiolipin/anti-beta2 glycoprotein I-negative) and 25 LAC/aCL/anti-b2GPI-negative. All the serum samples were analysed for the anti-PT/PS IgG and IgM antibodies using the new ELISA method under development by Inova (San Diego, CA). Fifty-two samples were analysed also for IgG/IgM anti-prothrombin autoantibodies by the routinely used method (Orgentec, Mainz, Germany).
Results Overall, the Inova ELISA test revealed a high prevalence of the anti-PT/PS antibodies amongst LAC positive patients (anti-PT/PS IgG and/or IgM positive in 64/108, 59.3% of LAC-positive patients versus 4/52, 7.7% of controls; p<0.001). This prevalence was in line with that awaited (1). Globally, patients with SLE, UCTD or APS, were 47/83 (56.6%) anti-PT/PS positive. The percentage increased when considering only the LAC-positive cases (39/53, 73.6%). Compared to the routinely used IgG/IgM anti-prothrombin assay, the new anti-PT/PS complex assay confirmed 5/8, 62.5% of the positive samples, but was able to identify another 24 (46.1% of the 52 cases analysed with both assays) new positive cases, who were all SLE/UCTD/APS patients.
Conclusions As reviewed by Amengual et al (1), the antibodies more closely associated with APS and LAC are directed to the complex between PT and anionic phospholipid (such as PT/PS) rather than PT alone. The new anti-PT/PS complex antibodies assay by Inova improves the capability to identify such reactivity and may help to better characterize patients with APS.
Amengual O. et al, Arthritis & Rheum 2003.
Disclosure of Interest None Declared