Association of Hospitalization Due to Vaso-Occlusive Crisis with Subsequent Sickle Cell Disease-Related Organ Damage Hospitalization: Retrospective Analysis of 3-Year Observational Study Data

Background: Hospitalization due to vaso-occlusive crisis (H-VOC) is common in individuals with sickle cell disease (SCD), with an increasing occurrence of SCD-related complications, including organ damage, as the disease progresses. Evidence regarding the relationship between H-VOC and SCD-related organ damage, however, is lacking.

Aim: To assess whether H-VOC is associated with hospitalization due to SCD-related organ damage, through retrospective analysis of data collected prospectively during a 3-year, multicenter, observational US study (NCT01220115) that aimed to better understand disease burden and management of SCD in individuals aged ≥2 years.

Methods: Of the 498 individuals with SCD who were recruited into the US study, data were analyzed from 202 (100 men and 102 women) who were aged ≥16 years and had available hospital admission data. Organ damage was defined based on hospital discharge diagnosis. ¹ Variables tested at baseline, in addition to H-VOC, included demographics, blood measures, and treatment history. Age and sex were included by default in all models based on literature suggesting they are relevant factors influencing organ damage. Hazard ratios (HRs) for the time from H-VOC to the first subsequent hospitalization due to SCD-related organ damage were estimated using multivariable Cox regression. Worsening of pre-existing organ damage was not considered as an event due to potential confounding (ie worsening of organ damage related to the pre-existing condition rather than as a consequence of the VOC).

Results: During median 3-year follow-up, 55 (27%) individuals experienced at least one hospitalization due to SCD-related organ damage; ² 19 (9%) had multiple visits. Within the 12 months preceding baseline, 22 (11%) individuals had a history of organ damage, there was a median of two H-VOC in the 90 (45%) individuals with history of H-VOC, and 43 (21%) individuals had received chronic transfusion (≥6). History of H-VOC (HR 2.54, 95% confidence interval [CI] 1.46 to 4.43 in past 12 months), genotype (HR 2.69, 95% CI 1.34 to 5.41 for HbSS), and sex (HR 1.90, 95% CI 1.08 to 3.34 for women) were all significantly associated with subsequent hospitalization for SCD-related organ damage.

Discussion and conclusion: This analysis demonstrates that history of H-VOC within the preceding 12 months is significantly associated with a higher rate of subsequent hospitalization due to SCD-related organ damage, independent of age, sex, and genotype, and may therefore help identify individuals at high risk of developing organ damage. Despite 21% of individuals receiving chronic transfusions at baseline, this factor did not remain significantly associated with the outcome when also considering genotype and H-VOC. Age and sex were unexpectedly insignificantly associated with the outcome; this is likely due to the relatively short follow-up time. Extending the historical timeframe of organ damage to 5 years did not change our findings, except that age also became significantly associated with subsequent hospitalization for organ damage. Acute chest syndrome and pneumonia were the most common types of historical (baseline) organ damage, whilst gallbladder disease was the most common organ damage observed during the follow-up period that was not observed at baseline. Our data have limited statistical power and generalizability; additional studies are required to confirm these findings. Nevertheless, our findings support the existing evidence of the impact that VOCs may have on individuals with SCD, and highlights the importance of preventing and reducing H-VOC.

¹Acute chest syndrome or pneumonia; avascular bone necrosis of hip(s), shoulder(s) or spine; cardiac failure; central nervous system disease (ie abnormal transcranial Doppler, silent infarct, stroke and transient ischemic attack); gallbladder disease; leg ulcer; liver disease (ie hepatic fibrosis/ cirrhosis, hepatic sequestration/sickle-hepatopathy/intrahepatic sickling, pulmonary fibrosis, pulmonary hypertension); priapism; renal disease (ie acute renal failure, chronic renal failure-supportive, dialysis, microalbuminuria/ proteinuria, transplant); retinopathy; and splenic sequestration.

²The top 3 reasons for hospitalization due to SCD-related organ damage were acute chest syndrome or pneumonia (n=29; 53%), renal disease (n=7; 13%) and gallbladder disease (n=6; 11%).

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