Acute Care Utilization and Rehospitalizations for Sickle Cell Disease FREE

Sickle cell disease is characterized by vasoocclusive complications, most commonly episodic periods of severe pain, leading to high use of health care resources.^1- 3 Although previous studies have described the magnitude of this health care utilization, they have generally been restricted to select populations of patients with sickle cell disease and therefore have limited generalizability and an inability to provide population-based estimates.^1- 4

Rehospitalization within 30 days has emerged as a clinical indicator of the quality of care for a variety of diseases.^5- 9 Thirty-day rehospitalization rate was recently adopted as a quality indicator for sickle cell care.^10- 12 However, the measure has not been validated, and there is skepticism about 30 days being the appropriate length of time over which to evaluate rehospitalizations for quality of sickle cell care.^12- 13 With only small single-payer or single-institution studies, there is a lack of benchmark information concerning rehospitalization rates for the sickle cell population.^10,14

The goals of this study are (1) to provide a comprehensive, generalizable estimate of the acute care utilization pattern for patients with sickle cell disease and (2) to estimate rates of rehospitalization and rates of treat-and-release emergency department (ED) visits following hospitalization that reflect a large percentage of patients with sickle cell disease across the United States. This information will facilitate the development of quality measures and provide population-based benchmarks for utilization and rehospitalization.

Encounter data were abstracted from the 2005 and 2006 Healthcare Cost and Utilization Project (HCUP) State Inpatient Databases (SID) and State Emergency Department Databases (SEDD) maintained by the Agency for Healthcare Research and Quality.^15- 17 The SID include all inpatient discharges from short-term, acute-care, nonfederal, general, and other specialty hospitals in participating states, including those discharges admitted from the ED. The SEDD include all treat-and-release and transfer ED visits (ie, did not result in inpatient hospitalization in the same hospital) from short-term, acute-care, nonfederal, community hospitals in participating states. The discharge and visit records from these databases contain information collected as part of billing records, including patient demographics, International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) diagnoses, expected payer, admission and discharge dates, and disposition.

Data were used from the 8 geographically dispersed states (Arizona, California, Florida, Massachusetts, Missouri, New York, South Carolina, and Tennessee) that had a sufficient number of people with sickle cell disease (defined as ≥10 patients in the majority of age and insurance categories) and provided encrypted identifiers. All health care encounter records (for inpatient stays and ED visits) for patients aged 1 year and older with a principal or secondary ICD-9-CM diagnosis of sickle cell disease (282.41, 282.42, 282.60-282.64, 282.68, or 282.69) were extracted (n = 151 074). Children younger than 1 year were excluded because of an inability to reliably link records. Records were linked using an encrypted patient-level identifier, age, and sex to create patient-level encounters, and all additional records (n = 23 333) for those patients were extracted regardless of diagnosis. Hospital stays and ED visits were then classified as sickle cell related as defined by 9 Clinical Classification Software codes and 91 ICD-9-CM codes.¹⁸ Any non–sickle cell–related encounter was removed from further analysis (see eAppendix for detailed description of population and utilization algorithm).

Visits to the ED that resulted in transfer to another institution were linked to the hospital record from that institution and recorded as hospitalizations. Therefore, all analyses reporting ED visits are treat-and-release ED visits only. In the 8 states, 23 171 patients with sickle cell disease were identified. Patients who died at any encounter (n = 463) were excluded from all analyses to eliminate higher potential utilization rates near death. Out-of-state residents (n = 1032) were excluded to provide population-based utilization rates.

Primary Outcomes. The primary outcomes were rates of (1) acute care utilization (hospital stays and treat-and-release ED visits) and (2) acute care utilization following a hospital discharge, with rehospitalization rates as the main outcome of interest.

Acute care utilization rates, defined as the number of encounters (hospital stays and treat-and-release ED visits) over the 2-year study period (January 2005 to December 2006) divided by 2, were calculated at the patient level. The rate, based on those with encounters, was analyzed by age group and expected payer. Population-based acute care utilization rates were calculated based on population estimates drawn from previously published work.¹⁹ The population estimates for each state were derived by applying the mortality-adjusted prevalence rates of sickle cell disease to the census estimates of each state's population. The published estimates for the 8 states were summed to yield the denominator for the study population. In addition to presenting rates as continuous variables, and similar to previously published groupings,¹ acute care utilization rates were also divided into groups based on number of encounters per year: 0, more than 0 but less than 1, 1 or more but less than 3, 3 to 10, and more than 10.

Rates of return for acute care include rehospitalization and treat-and-release ED visits following a hospital discharge, analyzed at both the encounter level and the patient level. Time between hospitalizations or between hospitalization and treat-and-release ED visit was calculated by subtracting the admission date of the subsequent encounter from the discharge date of the previous/index hospital stay. Encounter-level analyses were conducted for 30-day rehospitalizations, ED visits following hospitalization, and return to any site of care (ED or inpatient). A hospitalization could be followed by both a treat-and-release ED visit and a separate rehospitalization; thus, the rates of return for any acute care are not the sums of the ED and rehospitalization percentages. Because the appropriate timing at which to evaluate rehospitalization as a quality measure for sickle cell disease is controversial,^12- 13 14-day return rates were also derived.

Patient-level rehospitalization analyses were performed to determine the percentage of patients who were ever rehospitalized within 14 or 30 days. Although included for the acute care utilization analyses, the 2872 hospital discharges in December 2006 were excluded from rehospitalization analyses because complete 30-day follow-up information was not available.

Age, Expected Payer, and Length of Stay. The age of the patient was the age at the first encounter. Similar to previously published subgroups,²⁰ the following age groups were examined: 1 to 9 years, 10 to 17 years, 18 to 30 years, 31 to 45 years, 46 to 64 years, and 65 years and older.

Primary expected payer was available on each encounter record (eAppendix). We collapsed primary expected payer into 4 categories: public insurance (Medicaid or Medicare), private insurance, other or unknown insurance, and uninsured (self-pay or no charge). Encounter-level utilization rates were calculated based on the primary expected payer for each encounter. Rates of return for acute care were calculated based on the primary expected payer for the index hospitalization. For the patient-level analyses, expected payer was determined by the primary expected payer at the majority of encounters.

Length of stay for hospitalizations was determined by subtracting the discharge date from the admission date. For hospitalizations that began in the ED, ED time was not included.

Analytic Plan . Rates of acute care utilization are the number of encounters per patient per year and are stratified by age and payer. Population-based acute care utilization rates are based on sickle cell population estimates for the 8 states. Rates of return for acute care are presented for both 30 and 14 days. All hospitalizations and ED visits from these states are present in the databases; rates are presented for benchmarking purposes beyond the 8 states and include 95% confidence intervals (CIs). Confidence intervals could not be calculated for population-based analyses since those without utilization were estimated from another publication¹⁹; therefore, the numerator and denominator used to derive population rates have different standard errors. Rates are also presented for the subset of hemoglobin SS (Hb SS) patients, identified by having an Hb SS ICD-9-CM code (282.61, 282.62) and no code for another genotype. To evaluate the association between length of stay and rehospitalization, we compared the lengths of stay for hospitalizations resulting in a subsequent rehospitalization with hospitalizations not resulting in rehospitalization. The study and a waiver of patient consent were approved by the Medical College of Wisconsin institutional review board. Analyses were conducted using Base and /STAT software of SAS for Windows (version 9.2, SAS Institute Inc, Cary, North Carolina).

The final population of patients with sickle cell disease with utilization included 21 112 patients. The 21 112 patients were well distributed across all but the oldest age group, and the majority (59.6%) were publicly insured (Table 1). Slightly more than 75% of the patients had Hb SS disease, and 80% of the patients with hospitalizations were Hb SS. Acute care utilization totaled 63 873 hospitalizations and 45 471 treat-and-release ED visits. Less than 0.5% of ED visits were longer than 1 day. The most common principal diagnoses for hospitalizations were sickle cell disease with crisis (76.9%) and pneumonia (3.9%); all other diagnoses were less than 2% of hospitalizations. For ED visits, the most common principal diagnoses were sickle cell disease with crisis (64.2%), sickle cell disease without crisis (3.8%), fever (3.1%), pain in limb (3.1%), abdominal pain (2.3%), and chest pain (2.2%); all other diagnoses were less than 2% of ED visits.

The 109 344 acute care encounters by 21 112 patients yielded an acute care utilization rate of 2.59 (95% CI, 2.53-2.65) encounters per patient per year, 1.52 (95% CI, 1.48-1.55) encounters for hospitalizations and 1.08 (95% CI, 1.04-1.11) for treat-and-release ED visits. For patients with Hb SS, the acute care utilization rate was 2.67 (95% CI, 2.60-2.74) encounters per patient per year. The acute care utilization rate for all patients with sickle cell disease, stratified by age, is shown in Table 2. The 1- to 9-year-old children had 1.50 (95% CI, 1.45-1.55) encounters per patient per year, of which approximately 60% were inpatient hospitalizations. The rate of acute care utilization was highest, 3.61 (95% CI, 3.47-3.75) encounters per patient per year, for 18- to 30-year-olds, before decreasing throughout middle and older age. Between 55% and 69% of encounters for each age group were inpatient hospitalizations.

Table 3 shows the acute care utilization rate stratified by age and payer. Patients with public insurance had more encounters than those with private insurance, 3.22 (95% CI, 3.13-3.31) encounters per year vs 1.76 (95% CI, 1.68-1.84) encounters per year. The patients with no insurance had 1.42 (95% CI, 1.33-1.51) encounters per year. More than half of acute care encounters for publicly insured and privately insured patients were hospitalizations while only 44% of encounters by uninsured patients were hospitalizations. The discrepancy in rates between those with public insurance and private insurance was most notable in adults, with publicly insured adults experiencing twice as many acute care encounters. The highest acute care utilization rate was 4.80 (95% CI, 4.58-5.02) encounters per patient per year for publicly insured 18- to 30-year-olds.

Statewide estimates yielded an 8-state sickle cell population of 30 385.¹⁹ Given 21 112 patients had acute care encounters, and 463 died, an estimated 8810 (29.4%) of patients had no sickle cell–related hospitalizations or ED visits. Table 4 shows the population-based grouped acute care utilization rates stratified by age. Per year, 25.2% of people had more than 0 and less than 1 encounter and 13.7% had 3 to 10 encounters. Approximately 34% of children had no encounters compared with 12.0% of 18- to 30-year-olds. The percentage of patients with 3 or more encounters per year was highest in 18- to 30-year-olds. Including those with no encounters, the overall acute care utilization rate was 1.82 encounters per patient per year. Stratification by age revealed the following rates of encounters per patient per year: 1- to 9-year-olds, 0.99; 10- to 17-year-olds, 1.31; 18- to 30-year-olds, 3.18; 31- to 45-year-olds, 2.12; 46- to 64-year-olds, 1.08; and those 65 years and older, 0.77.

The 30-day rehospitalization rate was 33.4% (95% CI, 33.0%-33.8%); the 14-day rehospitalization rate was 22.1% (95% CI, 21.8%-22.4%). For patients with Hb SS, these rates were 31.7% (95% CI, 31.3%-32.1%) and 20.6% (95% CI, 20.2%-21.0%), respectively. Approximately 80% of all rehospitalizations were to the same hospital; this differed by age, with 94% of children rehospitalized at the same facility compared with 77% of adults.

In addition to rehospitalizations, 15.0% (95% CI, 14.7%-15.3%) of hospital discharges were followed by a treat-and-release ED visit within 30 days; overall, 39.6% (95% CI, 39.2%-40.0%) of hospital discharges resulted in a 30-day return for acute care. The 14-day rate of return for any acute care was 25.3% (95% CI, 24.9%-25.7%). Of the 61 070 hospitalizations eligible for return for acute care analysis, 53 258 (87.2%) had a diagnosis of sickle cell with crisis. For the subset with crisis, rehospitalization rates and return for acute care rates were similar to those for all discharges.

Table 5 shows both the 30- and 14-day rates of return for acute care. Hospitalizations for children aged 1 to 9 years were followed by a 4.1% (95% CI, 3.6%-4.6%) rate of return for a treat-and-release ED visit and a 12.8% (95% CI, 12.0%-13.6%) 30-day rehospitalization rate, with 16.1% (95% CI, 15.2%-17.0%) of hospital discharges followed by a return for any acute care within 30 days. The 30-day rehospitalization rate was highest, 41.1% (95% CI, 40.5%-41.7%), for 18- to 30-year-olds, for whom almost half of all hospitalizations resulted in a return for sickle cell–related acute care within 30 days. Thirty-day returns for acute care by expected payer revealed that hospitalizations of publicly insured patients had a 37.0% (95% CI, 36.6%-37.4%) 30-day rehospitalization rate, and 43.7% (95% CI, 43.2%-44.2%) of hospitalizations resulted in a return for any acute care within 30 days. The rates of return for acute care were substantially higher for publicly insured patients than privately insured, other insured, and uninsured patients.

The highest 14-day rehospitalization rate was 28.4% (95% CI, 27.8%-29.0%) for 18- to 30-year-olds. The 14-day return for acute care rates by expected payer showed publicly insured patients had the highest 14-day rehospitalization rate at 24.6% (95% CI, 24.2%-25.0%). Hospitalizations for privately insured patients had the lowest return rates.

Rehospitalizations at the patient level, showing the percentage of patients who had ever been rehospitalized, revealed similar patterns. Percentages of patients ever rehospitalized within 30 and 14 days were as follows: 1- to 9-year-olds, 30 days, 22.3% (14 days, 14.3%); 10- to 17-year-olds, 30 days, 32.8% (14 days, 24.2%); 18- to 30-year-olds, 30 days, 45.4% (14 days, 37.1%); 31- to 45-year-olds, 30 days, 37.4% (14 days, 29.5%); 46- to 64-year-olds, 30 days, 26.7% (14 days, 18.9%); and those aged 65 years and older, 30 days, 16.3% (14 days, 11.3%). Analysis by payer revealed the following rates: publicly insured, 30 days, 39.6% (14 days, 30.7%); privately insured, 30 days, 26.9% (14 days, 19.7%); uninsured, 30 days, 22.9% (14 days, 17.7%); and other or unknown, 30 days, 27.2% (14 days, 19.2%).

Hospitalizations that were followed by a rehospitalization within 30 days had an average length of stay of 6.1 days (95% CI, 5.3-6.9), compared with 5.6 days (95% CI, 5.0-6.2) for those without a subsequent rehospitalization. For 14-day rehospitalizations, the lengths of stay were 6.1 days (95% CI, 5.1-7.1) and 5.7 days (95% CI, 5.1-6.3), respectively.

Our population-based study of 21 112 patients with utilization related to sickle cell disease demonstrates high rates of acute care utilization and rehospitalization. Our study shows 1 in 4 patients with sickle cell disease experienced no acute care encounters and almost 1 in 5 patients experienced 3 or more encounters per year. This stands in contrast to the original evaluation by Platt et al¹ of acute care visits by the sickle cell population, which reported that, over a 5-year period, approximately 38.5% of patients with sickle cell disease did not seek acute care, and only 5.2% had 3 to 10 visits per year. While utilization definitions in the studies varied slightly, the higher utilization in our study may be explained by the inclusion of many patients who do not benefit from the type of comprehensive care that was provided during the Cooperative Study of Sickle Cell Disease.¹ Therefore, our findings likely provide a more representative depiction of current acute care utilization rates by patients with sickle cell disease.

The 30-day and 14-day rehospitalization rates in our study, and the overall rates of return for acute care, are also high. One in 3 patients with sickle cell disease was rehospitalized within 30 days, higher than studies for other diseases, including asthma (3.4%), pneumonia (12%), heart failure (16%), and diabetes mellitus (20%).^5- 8,21 The large number of eligible hospitalizations provides reliable benchmark rehospitalization rates. Previously reported sickle cell–related 30-day rehospitalization rates include a 50% rehospitalization rate for adults and a 30% rehospitalization rate for children.^10,14 Both of these were single-center studies with small numbers of patients, and both reported higher rehospitalization rates than our study. In addition, neither study provided information on 14-day rehospitalizations, which may be a more appropriate time interval to assess quality of care related to a hospitalization. In contrast, 30-day rehospitalization may be a more appropriate time interval to assess the quality and access to ambulatory care. It has been proposed that outpatient follow-up within 30 days may prevent rehospitalizations.^6,10 However, our study shows that two-thirds of patients rehospitalized within 30 days were rehospitalized within 14 days. Prevention of rehospitalizations within 14 days may require evaluation and intervention during the hospitalization, while prevention of rehospitalization at 30 days will require access to high-quality, comprehensive outpatient care. Of note, a shorter length of stay was not evident with rehospitalization; lengths of stay were similar whether a discharge was followed by a rehospitalization or not.

To our knowledge, this is the largest study to date that assesses acute care utilization for people with sickle cell disease. With data for more than 21 000 patients with sickle cell disease from states with sickle cell populations totaling more than 30 000, the study provides data for more than one-third of patients with sickle cell disease in the United States. By conducting multistate, all-payer, all-ages analyses, we provide comprehensive data regarding health care utilization for others to use when evaluating the care received by their patients with sickle cell disease. Our evaluation of patients with Hb SS revealed that 75% of patients in the utilization database were Hb SS, suggesting a higher level of utilization across the entire population in this subgroup, as their percentage of the sickle cell population is substantially lower than 75%.^22- 23

Our study included both ED visits and hospitalizations. Failure to include the 47 319 ED visits that did not result in hospitalization would dramatically underestimate the burden of acute care utilization for patients with sickle cell disease. Previous studies have limited their evaluations to inpatient data.^2,20,24 In addition to not including ED data, these studies lacked patient-level analyses and were unable to follow up patients over time to determine utilization patterns. Prior studies reported increasing hospitalizations with increasing age throughout childhood.^2,20,24- 25 Our study confirmed those findings but also found large differences by age and payer for acute care utilization, with patients aged 18 to 30 years and patients with public insurance experiencing the highest utilization rates. It is likely that the increased acute care utilization rate in this age population compared with older individuals reflects the fact that those with severe disease die earlier, leaving fewer people with severe disease as the population ages.¹⁹

Evaluation by expected payer revealed that the uninsured were more similar to those with private insurance than those with public insurance. While the high rate of utilization for those with public insurance is concerning for a lack of access to other (non-ED or inpatient) sources of care, the lower utilization rate for the uninsured may be an indicator that patients are not seeking necessary care because of inability to pay. An uninsured person, for example, may be more reluctant to seek care for the same level of illness or severity of pain than an insured individual.^26- 28 From these data, we cannot assess care-seeking behavior, quality of care, or alternate sources of care.

Our study is limited by not being a random sample of the national sickle cell population; however, the data do show all ED visits and hospitalizations for approximately 33% of the people with sickle cell disease in the United States. Additionally, at least 1 state from each geographic region of the country is included, and the age and insurance distributions of the hospitalizations closely mirror a national study of hospitalizations for sickle cell disease.²⁰ Second, we were only able to measure acute care that occurred in the ED or inpatient hospital setting. Visits to physician offices or other ambulatory care sites are not included. Third, the “other” insurance category is ill-defined, including other government payers, TRICARE, and workers' compensation. Fourth, there are inherent limitations related to the use of administrative data, including the potential for errors in recording diagnoses and sickle cell genotype, and thus misclassification of encounters and number of encounters. Although errors are possible, Healthcare Cost and Utilization Project data are highly accurate, rigorously tested, and widely used to estimate diagnoses and visit frequency.^15,29- 31 Analyses by genotype in these databases have not been validated. Finally, we have not reported rates of return care after treat-and-release ED visits.

In conclusion, rates of acute care utilization and rates of return for acute care are both high in the sickle cell population. This is especially true for young adults who may be particularly at risk as their disease worsens and they transition from pediatric to adult care. By providing comprehensive, generalizable benchmarks and identifying high-risk subpopulations, these data can be used to inform efforts to improve quality of care and reduce morbidity in sickle cell disease.