Endothelial biomarkers were increased in the serum of CLS patients: Angiopoietin-2 (day 1: 9.9[6–17] vs. 3.7[3–6] ng/mL, P < 0.001), VE-Cadherin (day 1: 2[1.5–2.7] vs. 1.7[1.4–2.1] ng/mL, P < 0.001), Syndecan-1 (day 1: 234[132–506] vs. 66[47–103] ng/mL, P < 0.001), Heparan sulfate (day 1: 4.3[3–6] vs. 3[2–4] ng/mL, P < 0.001), and ICAM-1 (day 1: 386[269–576] vs. 216[176–313] ng/mL, P < 0.001) were higher among CLS patients. This evidence concerns the gene ICAM1 and capillary leak syndrome.