Sickle Cell Disease in Sweden - Prevalence and Resource Use Estimated through Population-Based National Registers

BACKGROUND

Sickle cell disease (SCD) is an autosomal recessive disorder characterized by abnormal hemoglobin. SCD causes hemolytic anemia, vaso-occlusion leading to vaso-occlusive crises (VOC) and contributing to organ damage and early death. SCD is most prevalent in sub-Saharan Africa and the Middle East, but also countries such as Brazil, India and US, have comparatively high frequencies of SCD. Global migration has contributed to a greater geographical spread. The prevalence of SCD in Sweden is unknown.

OBJECTIVE

The primary objectives of this study were to estimate the 1-year prevalence of SCD and SCD-associated resource use in Sweden. Secondary objectives were to estimate birth incidence, treatment patterns and survival.

PATIENTS

Patients with an ICD-10 diagnosis code for SCD (any D57 [excluding D57.3, sickle cell trait]) were identified from the Swedish Patient Registry (between January 1 ^st 2001 and June 30 ^th 2018). Patients were assessed for 1-year prevalence and resource use per calendar year for a follow-up period of 13 years (2006-2018).

METHODS

Patients were considered prevalent from birth or immigration to death or emigration. Resource use from specialized care, including all events recorded in the registry with any D57 as the main diagnosis was assessed in the follow up period 2006-2018 as number of outpatient visits and inpatient stays. Costs for this hospital resource use were estimated through remuneration amounts based on diagnosis related groups. Data on sick leave days and days with disability pension due to SCD in patients in working age (18-65 years) were retrieved from the Swedish Social Security Agency and costed with the mean salary in Sweden, plus social security contributions. Costs are reported in 2019 Swedish Krona (SEK, ≈$ 0.1).

RESULTS

One-year prevalence of all SCD diagnosis increased from 504 patients (5.53 per 100,000 population) in 2006 to 670 patients (6.55 per 100,000 population) in 2018. The 1-year prevalence of SCD patients ever recorded with an ICD-10 code for SCD with VOC (D57.0) increased from 139 patients (1.53 per 100,000 population) in 2006 to 260 patients (2.54 per 100,000 population) in 2018. The proportion of prevalent patients that were born in Sweden decreased over the years, from approximately 55% in the beginning of the study period to 45% in the end of the study period. The mean and median age of the SCD population decreased over the study period. Individuals with SCD and VOC were, on average younger than the other SCD (D57) subgroups.

Birth incidence was captured by calendar year 2006-2018 and was highest in 2007 with 15 children born with SCD. For Swedish-born children with SCD during the patient identification time (n=123), the mean time to identification in the registers was 2.6 years (SD 2.7, range 0-16 years).

Hospital outpatient visits and inpatient stays with SCD (all events with D57 recorded) as main diagnosis increased from 57 to 189, and 250 to 1,003, respectively, over the years 2006-2018. This corresponded to costs of inpatient care increasing from 1.4 million (M) SEK in 2006 to 7.3 M SEK in 2018 and costs of outpatient visits increasing from 0.9 M SEK in 2006 to 4.6 M SEK in 2018. The vast majority of costs were incurred in individuals ever recorded with a SCD with VOC diagnosis (D57.0). The most frequent hospital treatment was blood transfusion, with 8-11% of patients receiving transfusion in each year studied, especially common in SCD and VOC diagnosis. The prescribed treatment with the highest increase of uptake over the study period were hydroxyurea, vitamins and paracetamol in all SCD.

Individuals in working age had on average 2.3 days of sick leave per patient-year due to SCD (D57), and approximately 4% of these patients received disability benefits because of their SCD.

During the follow-up period, the median age at death was 74 years for all SCD and 69 years for SCD with crisis, this is 7-10 years and 12-15 years less compared to the Swedish general population respectively.

CONCLUSION

This study demonstrates that the prevalence, hospital resource use and associated costs have increased substantially in Sweden. In an era of emerging treatments for SCD we have for the first time comprehensively described epidemiological-, disease-related and economical aspects of SCD in Sweden.