Figure 4.

Patient-derived antiphospholipid antibodies with lupus anticoagulant activity interfere with international normalized ratio (INR) measurements. Pooled normal plasma (PNP; A) or pooled vitamin K antagonist-treated plasma with INR values at the low (A; ≈2.0), middle (B; ≈3.0), and upper (C; ≈4.0) parts of the therapeutic range were incubated with 0 to 400 μg/mL patient-derived antiprothrombin antibodies or anti–beta-2-glycoprotein I (aβ2GPI) antibodies. INR measurements were performed using STA-Hepato Prest (I), STA-NeoPTimal (II), STA-Neoplastin R (III), or point-of-care test (POCT; IV) INR reagents. INR ≈ limit of detection. aPT, antiprothrombin.