Background: Gout is a common cause of inflammatory arthritis in the United States, and its prevalence has increased in recent decades, especially among older adults. Older adults with gout are of particular interest because they tend to experience higher rates of tophi, an advanced stage of gout, than do younger patients.
Objective: For older adults with gout to (1) assess health care utilization and costs from a third-party payer perspective; (2) evaluate health care costs related to tophi; and (3) explore the relationship between elevated serum uric acid (UA) level, an indicator of disease control, and health care utilization.
Methods: Data were extracted from the Integrated Healthcare Information Services (IHCIS) claims database (1999-2005), which includes approximately 40 private health plans in the United States for approximately 13 million beneficiaries, about 4% of whom are aged 65 years or older. Patients were included in the study if they: (1) had 2 diagnoses of gout (International Classification of Diseases, Ninth Revision, Clinical Modification [ICD-9-CM] code of 274.xx) on separate medical claims or 1 gout diagnosis plus at least 1 gout-related pharmacy claim (i.e., allopurinol, probenecid, colchicines, or sulfinpyrazone); (2) were at least 65 years old at the first diagnosis date (study index date); and (3) had 1 year of continuous eligibility both before and after the study index date. A comparison sample of elderly members without gout was selected using a 1:1 match to gout patients based on age, gender, and geographic region. Individuals in the comparison group also had 1 year of continuous eligibility both before and after the study index date, defined as the same index date as the respective matched gout patient. Patients with possible tophi were identified from at least 1 medical claim with an ICD-9-CM code 274.8x (274.81=gouty tophi of the ear; 274.82 = gouty tophi of other sites except ear; 274.89 = gout with other specified manifestations) during the 12-month study period following the study index date. Additionally, a subgroup of gout patients with at least 1 serum UA measure was selected. Patients were divided into 3 groups according to their serum UA level on the earliest test date (serum UA index date): low (< 6 mg per dL), moderate-high (6-8.99 mg per dL), and very high (> or = 9 mg per dL). Health care utilization was categorized into inpatient services, outpatient services, emergency room services, other medical services, and use of prescription drugs. Medical services were classified by the place of service indicated in the claim. Medical services costs and pharmacy costs were defined as the amount paid to the provider plus member cost share (e.g., deductible, copayment). Two types of costs were assessed in the analysis: total all-cause health care costs and gout-related costs, defined as costs associated with a claim with a primary or secondary diagnosis of gout (ICD-9-CM code 274.xx). Differences in total all-cause health care costs were calculated by comparing (1) gout patients and gout-free members during the 12-month period following the study index date; (2) gout patients with and without tophi during the 12-month period following the study index date; and (3) gout patients across the 3 serum UA categories during the 12-month period following the serum UA index date. Multivariate regression analyses were used to control for patients' baseline demographics, prior comorbidities indicated by the Deyo-Charlson Comorbidity Index, and number of medications used during the 12 months prior to the study index date.
Results: Over the 7 years of claims data through 2005, there were 11,935 gout patients aged 65 years or older. The sample had an average age of 71.4 years and was predominantly male (73.5%). In the 12 months following the study index date, the mean unadjusted per-patient gout-related health care cost was $876 (standard deviation $3,373) in 2005 dollars, 5.9% of the total all-cause health care cost of $14,734 (SD $27,401) for gout patients. Unadjusted total 12-month all-cause health care cost for the gout-free members was $9,219 (SD $20,186). After statistical adjustment for comorbidities, the difference in total 12-month all-cause health care costs between gout patients and gout-free members was $3,038 (P < 0.001). A diagnosis suggesting possible tophi was found in 2.0% (n = 240) of gout patients in the sample. After statistical adjustment for comorbidities, the difference in total 12-month all-cause health care costs between gout patients with and without tophi was $5,501 (P < 0.001), and the difference in total adjusted 12-month gout-related costs between patients with and without tophi was $1,710 (P < 0.001). Among the 2,237 (18.7%) patients with at least 1 serum UA measure, 28.3% had a low serum UA level, 52.4% had a moderate-high serum UA level, and 19.3% had a very high serum UA level. For patients with low, moderate-high, and very high serum UA levels, regression-adjusted gout-related costs in the 12 months following the serum UA index date represented, respectively, 2.9%, 2.7%, and 3.9% of total regression-adjusted health care costs. The group with a very high serum UA level had significantly higher regression-adjusted total 12-month all-cause health care costs and gout-related costs compared with those with a low serum UA level ($3,103 and $276 higher, respectively).
Conclusions: Elderly patients with a diagnosis of gout have higher all-cause health care utilization and costs compared with matched elderly patients without a diagnosis of gout. Gout-related costs represent about 6% of total health care costs in elderly patients with gout. Very high serum UA levels (i.e., > or = 9 mg per dL) and diagnoses suggesting possible tophi are associated with increased utilization and costs in elderly gout patients.