Estimated length of stay calculated by “diagnosisrelated groups” in patients with prostate cancer: a retrospective analysis

Diagnosis-related group (DRG) is a classification based on patient diagnosis and illness severity that is used as a care performance indicator and to analyze hospital costs.(1) In the United States, it has been used as a system of prospective payment for Medicare reimbursement since the 1980's.(2) Moreover, as new technologies and treatments have been developed, the DRGs have been updated, with several new editions published over the years.(3) In Brazil, however, the DRG system has only been implemented in the last 10 years, which is consistent with the epidemiological reality of the country.

Prostate cancer (PCa) is one of the most common malignancies in men worldwide.(4) Tumor stage and patient performance status dictate the treatment strategy, which may vary from surgery and radiotherapy with curative intent to chemotherapy and androgen-deprivation therapy (ADT) for disease control in the metastatic setting.(5) Several promising options have emerged for later-line treatment of recurrent or metastatic PCa. Recent clinical trials with abiraterone and enzalutamide have demonstrated benefits regarding overall survival, while apalutamide also showed increased metastasis free-survival in castration-resistant PCa (CRPCa).(6 7 8 9) However, new treatments and longer survival have been associated with increased costs, especially in patients with metastatic cancer. One recent study estimated that health costs have been increasing by almost US$9,000 per month per patient when using new lines of treatment.(10) Additionally, patients with PCa diagnosed with bone metastasis now have a mean overall survival of 7.5 years.(11)

Although several parameters have a higher impact on case-mix weight and are associated with increased hospital costs, length of stay (LOS) is among the most important variables of interest during hospitalization that are used by the DRG system. Increased LOS may be caused by disease-related factors or hospital-related circumstances, such as access to healthcare or even the day of the week a patient is admitted.(8) For example, Panagiotopoulos et al. (ANO)^(x) analyzed oncologic DRGs in an internal medicine department and found that LOS was the main factor for hospital under-reimbursement. Furthermore, inpatient facility costs are the largest component of medical resource utilization in patients with metastatic PCa, demonstrating that disease progression is directly associated to a higher economic impact.(12)

It is well established that patients with PCa with or without metastasis demand an increased amount of financial resources, mainly because of new treatment technologies, prescription of novel drugs, or the presence of skeletal-related events.(13) However, it is not completely understood whether the DRG system is able to predict and explain the differences in LOS in case-mix groups.(14) To date, there are no data comparing length of hospitalization for any cause in patients with PCa, with or without metastasis, adjusted by confounders. Therefore, we sought to compare whether hospital admissions of patients diagnosed with PCa and bone metastasis are associated with increased LOS when compared to DRG- estimated, in a population of patients receiving regular outpatient care who required hospital admission for any cause.

A total of 86 hospital admissions were studied. Mean age was 76.6 (±9.4) years, and mean BMI was 25.9 (±5.8) kg/m² (Table 1). Among all medical hospitalizations, urology was the most commonly represented specialty, accounting for 31.4% (27 admissions), followed by clinical oncology with 30.2% (26 admissions) (SupplementaryTable 1). The most frequent ICD-10 on hospitalization was PCa (N=24); however, there were 50 different ICD-10 codes described at admission (SupplementaryTable 2). Mean LOS was significantly higher in the overall sample when compared to estimated DRG-LOS (7.5±7.3 and 4.4±2.9, p =0.014) (SupplementaryTable 3). Group 2 (LOS>DRGLOS) was significantly associated with admission for clinical treatment (OR=3.54, 95% CI=1.40-8.91, p =0.007) and admission at ICU during hospitalization (OR=5.37, 95% CI=1.58-17.8, p =0.007). (Table 2). The prevalence of bone metastasis in groups 1 and 2 was 31.1% and 68.3%, respectively. Bone metastasis was positively associated with group 2 status (LOS>DRGLOS) on univariable and multivariable analysis (OR=4.76, 95% CI=1.91-11.8, p =0.001 and OR=3.48, 95% CI=1.08-11.2, p =0.03, respectively) (Table 3). Others baseline characteristics were not significantly different between groups 1 and 2. All patients were alive at discharge.

DRGs are one of the most important tools to analyze optimal allocation of medical resources in healthcare systems.(1) First utilized in the U.S. in the 1980s, DRG coding started to be used in healthcare systems in several other countries in the last decades.(15) DRGs are formulated based on the diagnosis (divided into major diagnostic categories), type of admission (clinical or surgical), and comorbidities, which generate codes and estimate LOS for each case.(1 16) More recently, this system has been used to support quality improvements and the achievement of higher efficiency in healthcare.

PCa has an important impact on financial resources utilization due to its high prevalence and incidence. Worldwide, more than 1.3 million patients were diagnosed with PCa in 2018 alone.(4) In addition, major advances in treatments with curative intent and new medications to manage disease recurrence or control metastasis have not only improved overall survival and quality of life, but also increased costs.(11) However, whether the presence of recurrent PCa or metastatic disease has any impact on the homogeneity of DRG system categorization is still a matter of debate. Therefore, we sought to evaluate whether patients with PCa and bone metastasis had a longer actual LOS when compared to estimated DRG-LOS on admission when hospitalized due to any cause. We found that admissions of patients with PCa and bone metastases were significantly associated with increased duration of hospitalization when compared to the estimated DRG-LOS.

LOS is an important metric to evaluate costs in healthcare.(17) Additionally, some studies have demonstrated that LOS may be associated with increased costs of clinical and surgical hospitalizations.(8 18 19) For instance, Fine et al. (2000),(18) in a multicenter study analyzing patients admitted with community-acquired pneumonia, revealed considerable cost savings with as little as a 1-day reduction in LOS. Moreover, a recent review of 37 studies indicated that enhanced recovery programs versus conventional management decreased the LOS after abdominal surgeries and were substantially associated with cost savings.(19) It seems that duration of hospitalization is directly correlated with consumption of health resources.

Although the majority of patients at the time of PCa diagnosis have localized disease, almost 30% will develop bone metastasis during follow-up.(20) In our study, among all admissions, PCa with bone metastasis was present in 42 (48.8%) and was independently associated with increased LOS. As long as patients with metastatic PCa have access to adequate treatment (androgen deprivation therapy), long overall survival and even increased metastasis free-survival can be expected for this group. Data from CaPSURE, which analyzed more than 12,000 patients from 1990 to 2004, found that PCa-specific survival at 5 years was 71% (95% CI=62-78).(11) A recent double-blind clinical trial that studied the androgen receptor inhibitor apalutamide in non-metastatic castration-resistant PCa found a significant survival free of metastasis when compared to placebo (HR 0.28; 95% CI=0.23-0.35).(21) Thus, given the fact that, in our study, PCa with bone metastasis was associated with a 3.48-fold increase in risk for longer LOS even after adjusting for other variables, it is plausible to think that new medications that prevent development of bone metastases may also lead to shorter LOS when these patients are hospitalized.

Analysis of patient characteristics that may increase or decrease LOS is of interest for hospital reimbursements and performance analysis. Some studies have evaluated factors that may influence these scenarios.(12 16) For example, in a large study that evaluated the duration of hospitalization of patients with acute coronary syndromes, the authors found that diabetes and cerebrovascular disease were directly associated with increased LOS, with a higher weight when compared to other comorbidities, and concluded that the presence of this two diseases should be linked to higher reim-bursement.(22) In another study, Freitas et al. (2012),(23) analyzed variables associated with LOS outliers in the Portuguese National Health Service and found that addition of each comorbidity in the statistical model resulted in an adjusted OR of 1.41. In our analysis, comorbidities were not correlated with actual LOS higher than estimated DRG-LOS. However, as we did not analyze specific types of comorbidities, further studies are necessary to assess the real impact of specific medical conditions during hospitalization in PCa patients.

Our study has some limitations. First, our data were collected from a single private hospital. Second, we selected only patients who were receiving regular outpatient follow-up at our clinic, to ensure data quality. Notably, the majority of patients who were hospitalized at our institution came from outside facilities, which restricted the number of admissions in our sample. Third, DRG coding and data were collected retrospectively. Finally, we did not study types of comorbidities or severity of bone disease, as indicated by pain or number of metastases.

To the best of our knowledge, this was the first study to analyze the association between LOS estimated by DRG and PCa. We found that, among admissions of patients diagnosed with PCa, the presence of bone metastasis was independently associated with significantly longer actual LOS when compared with LOS estimated by DRG. This finding has implications for hospital resources allocation and efficiency analysis. The advent of new medications that increase metastasis-free survival in patients diagnosed with recurrent non-metastatic PCa may decrease LOS when these patients are hospitalized. The presence of bone metastases may be used to identify possible outliers who are not recognized by the DRG system.