Table 2.

ELISA results

	Seropositive APS (n=40)	SN-APS (n=40)
Standard ELISAs
No. (%) testing positive for IgG anti-CL	18 (45%)	0
No. (%) testing positive for IgG anti-β2GPI	6 (15%)	0
No. (%) testing positive for IgM anti-CL	4 (10%)	0
No. (%) testing positive for IgM anti-β2GPI	9 (22.5%)	0
Anti-DI ELISAs
No. (%) testing positive for IgG anti-DI	11 (27.5%)	3 (7.5%)*
No. (%) testing positive for IgM anti-DI	9 (22.5%)	0
No. (%) testing positive for IgA anti-DI	7 (17.5%)	0
Other IgA ELISAs
No. (%) testing positive for IgA anti-CL	12 (30%)	0
No. (%) testing positive for IgA anti-β2GPI	8 (20%)	1 (2.5%)*

The cut-off for positive in each assay was defined as 99th centile of the healthy control population.

*The titres of IgG anti-DI in the three positive patients were 16 absorbance units (AU), 15.3 AU and 22.2 AU respectively compared with the positive cut-off of 10 AU. The titre of IgA anti-β2GPI in the one positive patient was 16 AU compared with a positive cut-off of 9 AU.

anti-β2GPI, anti-β-2-glycoprotein; CL, cardiolipin; DI, domain I; Ig, immunoglobulin; SN-APS, seronegative antiphospholipid syndrome.