PB0138 - Sensitivity and specificity of the mixing test in the identification of interference inhibitors (antiphospholipid antibodies) in asymptomatic patients.

Background: Interference inhibitors are immunoglobulins or other substances that, through various mechanisms, “interfere” with the in vitro coagulation process. They can be detected in asymptomatic individuals and in patients with antiphospholipid syndrome, among other pathologies, with the mixing test on prolonged aPTT using the Rosner Index (RI) being the first technique to be used in its study.

Aims: The objective is to assess the sensitivity and specificity of the mixing test, through the RI, in the detection of antiphospholipid antibodies: lupus anticoagulant (LA), anticardiolipin antibodies (AAC) IgM-IgG and anti B2-GPI antibodies (IgM-IgG) in asymptomatic patients.

Methods: A total of 132 asymptomatic patients with prolonged aPTT in at least two consecutive determinations have been analyzed retrospectively and single-centerly from 05-2018 to 05-2023 (who underwent a mixing test with determination of the RI and determination of antiphospholipid antibodies). Clinical and analytical data were collected.

Results: The median age was 57.3 years (8-95 years) with a slight predominance of females (53%). 45.5% had at least one identified cardiovascular risk factor. The median (in seconds) aPTT obtained was 43.6 s. In order of frequency, the most common antiphospholipid antibodies were LA (26.7%), AAC IgM (7.1%), Ac. Anti B2-GPI IgM (7.1%), AAC IgG (5.2%) and Ac. Anti B2-GPI IgG (1.8%). There was a testimonial representation of double positives (2.7%) and triple positives (0.9%), which prevented performing an inferential analysis in this subgroup of patients. There was a statistically significant correlation between a mixing test with a Rosner index >15% with the detection of AAC IgM (p= < 0.001) and IgG (p=0.02), with a sensitivity of 80.0% and a specificity of 66.7%.

Conclusion(s): The mixing test (with a RI >15%) is sensitive in the detection of interference inhibitors in patients with prolonged aPTT in asymptomatic patients, and there is also a statistically significant correlation with the identification of anticardiolipin antibodies (IgM-IgG).