Assessment of antiphospholipid antibodies and calprotectin as biomarkers for discriminating mild from severe COVID‐19

BACKGROUND: To explore the association of thrombo‐inflammatory biomarkers with severity in coronavirus disease (COVID‐19), we measured antiphospholipid antibodies (aPL) and calprotectin in sera of COVID‐19 patients. METHODS: Anticardiolipin antibodies (aCL) and anti‐β2‐glycoprotein I antibodies were measured using enzyme‐linked immunosorbent assay (ELISA) and multiplex flow immunoassay (MFIA) in hospitalized COVID‐19 patients (N = 105) and healthy controls (N = 38). Anti‐phosphatidylserine/prothrombin antibodies, calprotectin, and C‐reactive protein (CRP) levels were also measured. We assessed the potential correlation between calprotectin levels and various laboratory parameters that were measured during the hospitalization period. After stratifying COVID‐19 patients into two groups by their oxygenation status or acute respiratory distress syndrome presentation, the discriminatory performance of each biomarker was evaluated. RESULTS: A high proportion of COVID‐19 patients (29.5%, 31/105) had low aCL IgM titers that were detectable by ELISA but mostly below the detection limit of MFIA. Calprotectin levels in severe groups of COVID‐19 were significantly higher than those in non‐severe groups, while CRP levels revealed no significant differences. Serum calprotectin levels showed strong to moderate degree of correlation with other routinely used parameters including peak levels of CRP, ferritin, procalcitonin, BUN, and neutrophil‐to‐lymphocyte ratio, but a negative correlation with minimal lymphocyte count and CD4(+) T cells. The discriminatory performance was highest for calprotectin in discriminating severe groups of COVID‐19. CONCLUSIONS: Serum calprotectin levels were significantly elevated in severe COVID‐19 cases. The prevalence of clinically significant aPL did not differ. The link between calprotectin and inflammatory pathway in COVID‐19 may help improve the management and outcomes of COVID‐19 patients.