Is a Higher Body Mass Index a Risk Factor for Developing Antiphospholipid Antibody Syndrome?

Background: Antiphospholipid antibodies (aPLs) are antibodies directed against components of the cell membrane and can be associated with clinical features or be asymptomatic in 1-5% of the population. Objective: The objective of this study is to investigate the frequency of aPL positivity based on body mass index (BMI). Methods: This is a retrospective analysis of all aPL testing done in a tertiary center between 2010 and 2020. The difference between patients with BMI <25, BMI 25-30, and BMI>30 is calculated using chi-square or Fisher's exact test as appropriate for categorical variables and a two-sample t-test for numerical variables. Unadjusted then multivariable logistic regression models were conducted to evaluate the effect of BMI on aPL positivity adjusting for age, thrombosis history, pregnancy complications history, and presence of autoimmune disease. Sex was included as an effect modifier. Results: Among 312 patients, the outcome (any positive aPL) was detected in 26 (20.8%), 13 (13.0%), and 16 (18.4%) patients with BMI groups: BMI <25, BMI 25-30, and BMI > 30, respectively. A multivariable logistic regression showed that those with BMI 25-30 had a lower risk of aPL positivity when compared to patients with BMI <25 (OR of 0.55 CI 0.25 - 1.14, p=0.116), and patients with BMI >30 also carried a lower risk compared with patients with BMI<25 (OR of 0.76, 95% CI 0.36 - 1.56, p=0.46); these results were not statistically significant. Interpretation: The results suggest that a higher BMI was not a risk factor for aPL positivity. A better understanding of the complex interactions between antiphospholipid antibodies and obesity should be further investigated.