Clinical characteristics of the cohort:
During the 10-year period, a total of 21 hospital acquired VTE events were identified. No patient had documentation of a prior VTE. Table 1 summarizes the clinical characteristics of the cohort. Most common VTE location was isolated PE (n=9, 43%), closely followed by isolated DVT (n=8, 38%). There were 6 total lower extremity DVTs and 6 total upper extremity DVTs, with some patients having DVTs in both locations. Majority of subjects had HbSS or HbSβThal0 genotype (n=15, 71%). Age ranged from 1.5 years to 19.5 years, with a median age of 14 years. Fifty-two percent of the cohort were on hydroxyurea at the time of VTE (n=11). More than seventy percent of the VTE occurred in children with SCD who were 12 years and older (n=15).
Overall, more than half of the patients with VTE had ACS on admission or during hospitalization (n=11, 52%). Thirteen thrombotic events (62%) were associated with ICU admission. CVC-associated thrombosis was seen in 43% (n=9) of the cohort. CVC type was either tunneled catheters (n=8, 89%) or peripherally inserted central catheter line (n=1, 11%). Table 2 summarizes the risk factors sub-stratified into the two age groups for VTE. None of these clinical variables reached statistical significance, likely owing to small sample size. No patients reported the use of oral contraceptive pills or personal or family history of thrombosis.
Not all patients were tested for inherited thrombophilia, but among the ones who were tested, 3 (14%) patients had protein C deficiency, 1 (5%) patient had protein S deficiency, and 2 (9%) patients had antiphospholipid antibodies. Two patients with protein C deficiency were siblings with genetically proven diagnosis of heterozygous protein C deficiency. Sibling one had baseline protein C antigen and activity levels of 63% and 34% respectively, while sibling two’s baseline levels were never obtained once genetic diagnosis of protein C deficiency was made. The third patient with protein C deficiency had baseline protein C antigen and activity levels of 66% and 56% respectively; genetic testing was not performed. The patient with protein S deficiency had baseline protein S activity of 26% and did not undergo genetic testing. In the two latter patients, while the protein C and protein S levels were obtained in the acute thrombosis setting, repeat values months later were still below normal, which could be due to the baseline lower levels of protein C and protein S observed in patients with SCD.18 Regarding the 2 patients with antiphospholipid antibodies, 1 patient had systemic lupus erythematosus (SLE) along with positive anticardiolipin IgM and IgG antibodies and a lupus anticoagulant (positive by DRVVT and staclot) at the time of thrombotic event. While the anticardiolipin antibodies normalized 6 months later, this patient continued to have intermittent positive staclot, likely due to the underlying systemic lupus erythematosus (SLE). Anti beta2 glycoproteins IgG and IgM were normal. The other patient with antiphospholipid antibodies had positive lupus anticoagulant assays (DRVVT and staclot) with normal anticardiolipin IgG/IgM and anti beta2 glycoproteins IgG/IgM at the time of the thrombotic event. Repeat testing 3 months later showed normal levels of all 3 antibodies.