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‘Non-criteria’ antiphospholipid antibodies and thrombosis

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To the Editor: We read with great interest the excellent article on thrombosis secondary to antiphospholipid antibody syndrome. 1 We wish to comment on the section “Antiphospholipid antibodies are not all the same,” specifically on question 6: “Which of the following antiphospholipid antibodies have not been associated with an increased thrombotic risk?”

The answer offered was antiphosphatidylserine, and the authors stated, “While lupus anticoagulant, anti-beta-2-glycoprotein I, and anticardiolipin antibodies are associated with thrombosis, antiprothrombin antibodies (including antiprothrombin and antiphosphatidylserine antibodies) are not.” 1

Antiphospholipid antibody testing in antiphospholipid antibody syndrome is complicated, but we feel the information provided was inaccurate. It should be noted that 3 antibodies are under discussion: in addition to antiphosphatidylserine (aPS) antibodies, antiprothrombin antibodies are heterogeneous, comprising antibodies to prothrombin alone (aPT-A) and antibodies to the antiphosphatidylserine-prothrombin complex (aPS/PT). While the diagnostic utility of these antibodies is in evolution, there are numerous studies on their association with thrombosis or antiphospholipid antibody syndrome, or both. 2,3 Most recently, a systematic review (N = 7,000) concluded that prothrombin antibodies (aPT, aPS/PT) were strong risk factors for thrombosis (odds ratio 2.3, 95% confidence interval 1.72–3.5). 4

The revised Sapporo (Sydney) guidelines referenced by the authors addressed these “non-criteria” antiphospholipid antibodies. 5 At that time (2006), it was thought premature to include these antibodies as independent criteria for definite antiphospholipid antibody syndrome, even though their association with the syndrome was recognized by the committee. The guidelines considered an interesting scenario: What if a case fulfills the clinical criteria of antiphospholipid antibody syndrome, but serology is positive only for these “non-criteria” antibodies? It was suggested that these cases be classified as “probable” antiphospholipid antibody syndrome. Also, aPS/PT was proposed as a confirmatory assay for lupus anticoagulant testing.

In 2010, the International Congress on Antiphospholipid Antibodies concluded that aPS/PT is truly relevant to thrombosis and antiphospholipid antibody syndrome, with the possibility of aPS/PT becoming a criterion for the syndrome in the future. 6 Studies have already started on this. 7 Since then, 2 scoring systems to quantify the risk of thrombosis and obstetric events have incorporated aPS/PT—the Antiphospholipid Score (2012) and the Global Anti-Phospholipid Syndrome Score (2013). 8.9

In conclusion, these antibodies are associated with thrombosis, can be considered features of antiphospholipid antibody syndrome in the right clinical context, and have a role in contemporary discussion of this disease.

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