INTRODUCTION
Gout and rheumatoid arthritis (RA) are the 2 most common inflammatory arthritides. As hospitalizations for these conditions incur substantial resource use, hospitalization trends and associated costs provide key benchmarks of disease burden. However, relevant long-term data are scarce.
We evaluated US hospitalization trends of gout and RA from 1993–2011. We investigated these 2 arthritides simultaneously, as we hypothesized opposing trends (due to improvement in RA care and a worsening in gout epidemiology1 and suboptimal care2) and as each condition would serve as an internal comparison for the other.
METHODS
Hospitalization trends of RA and gout were studied using data from the 1993–2011 releases of the Nationwide Inpatient Sample (NIS), a database representative of hospitalizations in the United States.3 The NIS is a 20% stratified sample of all non-federal hospitals in the United States; sampling weights were used to obtain national estimates. Patients 18 years of age and older who were hospitalized during the study period with a principal discharge diagnosis of gout (ICD-9-CM codes: 274.0–274.9) or RA (ICD-9-CM codes: 714.0, 714.2, 714.30–714.33) were included. We focused on principal discharge diagnoses to capture hospitalizations for RA or gout, which also maximizes the validity of the case definition,4,5 and calculated annual population rates of hospitalizations and relevant surgeries (total knee replacement, total hip replacement, other major joint surgeries). We calculated inflation-adjusted hospital costs for gout and RA by merging the NIS charge data with cost-to-charge ratios (available after 2000) from the Healthcare Cost and Utilization Project. Statistical analyses included Poisson regression models using SAS Version 9.3. P-values were 2-sided with a significance threshold of <0.05. This study was exempt from review according to the Partners institutional review board.
RESULTS
There were 254,982 hospitalizations for gout (mean age, 66.7 years; 66.4% men) and 323,649 hospitalizations for RA (mean age, 61.0 years; 21.5% men) between 1993 and 2011. Demographic characteristics were similar over the study period.
From 1993 to 2011, the annual hospitalization rate for patients with a principal discharge diagnosis of RA declined from 13.9 (95% CI, 13.7–14.1) to 4.6 (95% CI, 4.5–4.7) per 100,000 US adults (p<0.001), whereas that for gout increased from 4.4 (95% CI, 4.3–4.5) to 8.8 (95% CI, 8.7–8.9) per 100,000 US adults (p <0.001) (Figure and Table). These trends persisted among age and sex subgroups (Table).
Figure 1.
Annual Rate of Hospitalization for Patients with a Principal Diagnosis of Gout and Rheumatoid Arthritis (RA)
Table 1.
Gout and Rheumatoid Arthritis Hospitalizations per 100,000 US Adults*
| Rate (95% CI) | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Year | 1993 | 1995 | 1997 | 1999 | 2001 | 2003 | 2005 | 2007 | 2009 | 2011 |
| Principal Diagnosis of Gout | ||||||||||
| Discharges, No | 8485 | 8028 | 8807 | 10160 | 12599 | 14712 | 16438 | 17361 | 16585 | 20949 |
| Overall | 4.4 (4.3–4.5) | 4.1 (4.0–4.2) | 4.4 (4.3–4.5) | 4.9 (4.8–5.0) | 5.9 (5.8–6.0) | 6.8 (6.7–6.9) | 7.4 (7.3–7.5) | 7.6 (7.5–7.8) | 7.1 (7.0–7.2) | 8.8 (8.7–8.9) |
| Age (years) | ||||||||||
| 18–44 | 1.0 (0.9–1.1) | 0.9 (0.8–0.9) | 0.9 (0.8–0.9) | 0.9 (0.9–1.0) | 1.1 (1.1–1.2) | 1.2 (1.1–1.3) | 1.3 (1.3–1.4) | 1.3 (1.3–1.4) | 1.2 (1.1–1.3) | 1.6 (1.5–1.6) |
| 45–64 | 4.9 (4.7–5.1) | 4.3 (4.1–4.4) | 4.6 (4.4–4.8) | 5.2 (5.0–5.3) | 5.7 (5.5–5.9) | 6.4 (6.2–6.6) | 6.8 (6.6–7.0) | 6.9 (6.7–7.1) | 6.3 (6.2–6.5) | 8.0 (7.8–8.2) |
| 65–84 | 13.9 (13.5–14.4) | 13.2 (12.8–13.6) | 14.0 (13.6–14.4) | 16.5 (16.0–16.9) | 19.8 (19.3–20.3) | 23.8 (23.3–24.4) | 25.1 (24.5–25.6) | 25.5 (24.9–26.0) | 23.7 (23.2–24.2) | 27.5 (27.0–28.0) |
| 85+ | 24.8 (23.1–26.4) | 23.2 (21.7–24.8) | 25.0 (23.4–26.6) | 23.3 (21.8–24.7) | 35.2 (33.4–36.9) | 32.9 (31.2–34.6) | 41.0 (39.2–42.9) | 43.4 (41.6–45.2) | 37.9 (36.2–39.5) | 48.3 (46.6–50.2) |
| Male | 6.1 (5.9–6.3) | 5.6 (5.5–5.8) | 5.7 (5.5–5.8) | 6.6 (6.4–6.7) | 8.0 (7.8–8.1) | 9.1 (8.9–9.2) | 10.4 (10.2–10.6) | 10.3 (10.1–10.5) | 9.8 (9.7–10.0) | 12.5 (12.3–12.7) |
| Female | 2.8 (2.7–3.0) | 2.6 (2.5–2.7) | 3.2 (3.1–3.3) | 3.4 (3.3–3.5) | 4.0 (3.9–4.1) | 4.6 (4.5–4.8) | 4.6 (4.5–4.7) | 5.2 (5.0–5.3) | 4.6 (4.5–4.7) | 5.3 (5.2–5.5) |
| Principal Diagnosis of Rheumatoid Arthritis | ||||||||||
| Discharges, No | 26712 | 22263 | 19880 | 17180 | 16996 | 15014 | 15461 | 13892 | 11944 | 11015 |
| Overall | 13.9 (13.7–14.1) | 11.3 (11.2–11.5) | 9.9 (9.7–10.0) | 8.3 (8.2–8.4) | 8.0 (7.9–8.1) | 6.9 (6.8–7.0) | 7.0 (6.9–7.1) | 6.1 (6.0–6.2) | 5.1 (5.0–5.2) | 4.6 (4.5–4.7) |
| Age (years) | ||||||||||
| 18–44 | 3.7 (3.6–3.8) | 2.5 (2.4–2.6) | 2.4 (2.3–2.5) | 2.4 (2.3–2.5) | 2.2 (2.1–2.3) | 2.3 (2.2–2.4) | 1.9 (1.8–2.0) | 2.0 (1.9–2.0) | 1.6 (1.6–1.7) | 1.5 (1.4–1.6) |
| 45–64 | 20.0 (19.6–20.4) | 15.1 (14.8–15.5) | 12.9 (12.6–13.2) | 10.3 (10.0–10.5) | 10.1 (9.9–10.4) | 8.7 (8.5–8.9) | 8.5 (8.2–8.7) | 7.4 (7.2–7.6) | 6.1 (6.0–6.3) | 5.5 (5.4–5.7) |
| 65–84 | 41.1 (40.4–41.8) | 36.3 (35.7–37.0) | 30.8 (30.1–31.4) | 25.3 (24.7–25.9) | 24.0 (23.4–24.5) | 19.2 (18.7–19.7) | 20.6 (20.1–21.1) | 16.4 (16.0–16.9) | 13.6 (13.2–14.0) | 12.0 (11.7–12.4) |
| 85+ | 15.4 (14.1–16.7) | 15.2 (13.9–16.4) | 14.5 (13.3–15.7) | 13.5 (12.3–14.6) | 12.9 (11.8–14.0) | 10.2 (9.3–11.2) | 11.3 (10.3–12.3) | 11.8 (10.8–12.7) | 9.4 (8.6–10.2) | 7.2 (6.5–7.9) |
| Male | 5.9 (5.7–6.0) | 4.9 (4.8–5.1) | 4.6 (4.4–4.7) | 3.8 (3.7–3.9) | 3.6 (3.5–3.7) | 3.1 (3.0–3.2) | 3.2 (3.0–3.3) | 2.8 (2.7–2.9) | 2.4 (2.3–2.4) | 2.1 (2.0–2.1) |
| Female | 21.3 (21.0–21.6) | 17.2 (17.0–17.5) | 14.7 (14.5–15.0) | 12.5 (12.3–12.7) | 12.1 (11.9–12.3) | 10.5 (10.3–10.7) | 10.5 (10.4–10.7) | 9.3 (9.1–9.4) | 7.7 (7.6–7.9) | 7.0 (6.9–7.2) |
Data of odd years are presented to display the overall trends of the entire study period. P-values for trends (based on all calendar years) were <0.001 for all subgroups in this table.
The annual hospitalization rate for joint surgeries in patients with a principal discharge diagnosis of RA steadily declined from 8.4 (95% CI, 8.3–8.5) to 2.1 (95% CI, 2.0–2.2) per 100,000 US adults (p<0.001). The corresponding surgery rates for gout were 0.09 (95% CI, 0.08–0.11) and 0.17 (95% CI, 0.15–0.19) per 100,000 US adults (2% of hospitalizations for gout).
From 2001 to 2011, the inflation-adjusted hospital costs per 100,000 US adults with a principal discharge diagnosis of gout increased from $34,457 (95% CI, $33,855–$35,059) to $58,003, (95% CI, $57,218–$58,788) whereas the costs for RA declined from $83,101 (95% CI, $81,852–$84,350) to $55,988 (95% CI, $54,942–$57,034).
DISCUSSION
Primary hospitalization rates for gout have increased substantially over nearly 2 decades in the United States, whereas those for RA have declined. In 1993, hospitalizations for RA were more frequent than for gout; however, these contrasting trends led to a higher hospitalization rate for gout than RA in 2011. These trends were reflected in the inpatient economic burden, and persisted across demographic subgroups. Our focus on principal diagnoses helped minimize misclassification, but may have missed cases that secondarily contributed to hospitalizations. The study spanned 19 years until 2011. Recent changes in the NIS were expected to result in decreases in trends; thus 2013 data were not included. There is no reason to believe trends have changed more recently.
The findings may reflect the suboptimal care received by gout patients2 and its increasing prevalence.1 Further, the findings provide a benchmark for RA care over the past 2 decades,6 including the reduced frequency of joint replacements and other major joint surgeries related to RA. While the RA data are encouraging, the gout findings suggest the need to improve care and prevention.
Acknowledgments
Funding and support
This work was supported in part from a grant from the National Institute of Arthritis and Musculoskeletal and Skin Diseases (R01AR065944)
Footnotes
Conflict of Interest Disclosures
The authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Dr. Choi has has received a research grant from Astra-Zeneca and served as a research consultant for Takeda, both unrelated to this manuscript..
Author contributions
Drs. Lim and Choi had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.
Study concept and design: Lim, Lu, Fisher, Choi.
Acquisition, analysis, or interpretation of data: All the authors.
Drafting of the manuscript: Lim, Lu, Rai, Choi.
Critical revision of the manuscript for important intellectual content: All the authors.
Statistical analysis: Lim, Lu, Choi.
Administrative, technical, or material support: Lim, Lu, Choi, Fisher, Oza.
Study supervision: Choi.
Role of the Funder/Sponsor:
The funding agency had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, and approval of the manuscript; and decision to submit the manuscript for publication.
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