Health Status

In general, health status measures describe a person’s functioning in one or more domains (e.g., physical functioning or mental well-being).

Health Assessment Questionnaire–Disability Index (HAQ-DI)

The HAQ-DI is a self-administered 20-question instrument that assesses a patient’s level of functional ability and includes questions on fine movements of the upper extremities, locomotor activities of the lower extremities, and activities that involve both the upper and lower extremities. The HAQ-DI score is determined by summing the highest item score in each of the eight domains and dividing the sum by 8, yielding a score ranging from 0 (no disability) to 3 (severe disability). HAQ-DI has been used in different observational studies in gout. Studies have shown that patients with chronic gout (without recent history of acute attacks) have mild disability—the HAQ-DI scores range from 0.54 to 0.61 where scores of less than 1.0 are indicative of mild functional disability. In pegloticase randomized controlled trials (RCTs), the patients with chronic moderate-to-severe gout had moderate disability (1.10 to 1.24). In contrast, patients with other rheumatic diseases (rheumatoid arthritis and scleroderma) have moderate-to-severe disability and are predictive of poor outcomes and survival. Patients in gout observational cohorts had a high ceiling effect (percentages of respondents scoring at the highest possible scale level) ranging from 28% to 34%, signifying no functional disability. This may limit its applicability in longitudinal clinical care. Utility of HAQ-DI in gout clinical care (especially in patients with acute gout) needs to be determined.

Patient-Reported Outcomes Measurement Information System (PROMIS)

The National Institutes of Health (NIH) Patient-Reported Outcomes Measurement Information System (PROMIS) Roadmap initiative ( www.nihpromis.org ) is a cooperative research program designed to develop, evaluate, and standardize item banks to measure patient-reported outcomes (PROs) across common medical conditions. The goal of PROMIS is to develop reliable and valid item banks using item response theory (IRT) that can be administered as computerized adaptive tests (CATs). A CAT selects the most informative questions from an item bank on the basis of a person’s previous responses; this process determines an individualized score using a minimum number of questions while preserving precision. Eleven adult domains have been developed to date as short forms and CATs in physical, mental, and social health and are available free to researchers at www.nihpromis.org . These CATs include anger, anxiety, depression, fatigue, pain behavior, pain impact, physical function, sleep disturbance, wake disturbance, satisfaction with participation in social roles, and satisfaction with participation in discretionary social activities (available at www.nihpromis.org ). NIH PROMIS scales have been successfully used in other chronic diseases including different arthritides. ²³

Health Value/Preference/Utility Measures

Health values assess the value or desirability of a state of health against an external metric, are generic HRQOL measures, and summarize HRQOL as a single number. There are two major families of utility measures: direct and indirect (also known as multiattribute utilities or health state classification systems). These values can be used for decision analysis and cost-effectiveness analysis. On an individual level, one’s own health utilities may be used to help make decisions regarding testing and treatment. Khanna et al. interviewed 80 subjects with gout and assessed direct preference based measures including a health rating scale, the time tradeoff, and standard gamble for one’s current health state with gout and current health state without gout; indirect preference-based measures including the SF-6D and the EQ-5D. Disutilities for chronic stable gout were small compared to other chronic conditions. However, the patients who rank their gout as their top health concern tended to assign greater disutility to gout than did other patients. In another ongoing study presented as an abstract, patients with tophaceous gout assigned a higher disutility to their health compared to patients without it. Further research is important in this area as new drugs are being developed for acute and chronic gout.

There is increasing evidence showing that inadequate control of gout results in continued suffering in a significant number of patients thus not only has detrimental effects on patient-reported outcomes but also confers substantial economic impact on the patient, employer, and society. The next section discusses the data on work productivity and health care utilization in gout.

Work Productivity

Kleinman et al. evaluated the impact of gout (defined by International Classification of Diseases [ ICD ] -9 code) on an employed population’s health-related work absence and objectively measured productivity output in a retrospective study. They used two comparison cohorts selected from the Human Capital Management Services Research Reference Database: a cohort of 300,000 employees with gout and without gout. Sick leave, short- and long-term disability, and workers’ compensation data were collected from employers during 2001 to 2004. Data on employee-specific at-work productivity that can be measured in units of work processed per hour for a subset of the overall population were analyzed for hourly productivity and a 12-month period (total annual productivity). Employees with gout had 4.6 more annual absence days for all categories of health-related work absence than did those without gout. Objective productivity (units of work processed) was available in 86 employees with gout. It showed that these patients processed 3.51% fewer units per hour worked and 2.38% fewer units per year than did employees without gout.

Edwards et al. recently assessed patient work productivity and social participation in chronic gout refractory to conventional therapy in a 1-year prospective observational study (N = 81). For patients who were less than 65 years of age, an average of 25.1 work days were lost annually. At least one flare per year was reported in 54% patients with a mean of 17.1 social days lost.

Work productivity using the Work Productivity Survey was assessed in an ongoing Veterans Administration cohort of tophaceous and nontophaceous gout patients to evaluate the impact of gout on productivity at home and in the workplace. The authors found that patients missed 3.7 days during the past month and had an additional 3 days with impaired productivity at work. Tophaceous gout was associated with greater loss of productivity at home and in the workplace compared to nontophaceous gout. The patients with tophi reported 4.5 days of work lost compared to 3.2 days per month in the non-tophaceous group and an additional 4.2 days of reduced productivity at home compared to 2.4 in the nontophaceous group. Thus, the literature conclusively suggests that gout negatively impacts workplace and home productivity.

Health Care Utilization

Patterns of health care utilization have been examined by Singh et al. across a variety of settings such as primary care, rheumatology, and emergency/urgent health care utilization in patients with gout in patients recruited from three large U.S. cities. The most utilized gout-related health care resource in the past year was primary care physicians, used by 60% of patients with a mean annual utilization of 3.1 visits, followed by visits to rheumatologists (51% of patients utilized with a mean annual number of visits of 3.7). Other providers such as nurse practitioners, physician assistants, urgent care, and emergency department resources were each used by about one-fourth of patients, averaging approximately two visits each in the past year. Overnight hospitalization for gout was reported by less than 10% of patients. Overall gout severity (physician defined), recent gout attack, elevated serum urate, and history of heart disease were significantly associated with whether patients utilized each resource category, with the exception of rheumatologist utilization. In another population of veterans in the United States, Singh and Strand showed that gout patients had significantly more annual primary care visits (3.5 versus 2.7) and hospitalizations (18% versus 15%) and fewer mental health visits (10% versus 14%, p < .01) compared to patients without gout.

Measurement Properties of an Instrument—Feasibility, Reliability, and Validity

An outcome measure should be feasible, reliable, and valid. A feasible measure is accessible, easily interpretable, and associated with low cost. Reliability (precision) is extent to which a measure yields the same score each time it is administered if the underlying health condition has not changed. A reliability coefficient of 0.90 or higher (means that 90% of the score is accurate while the remaining 10% denotes error) is considered satisfactory for individual comparisons and 0.70 or higher is considered satisfactory for group comparisons. Reliability can be assessed by conducting test-retest (where scores are assessed at two different time points) and assessing internal consistency (assesses correlation between items within each scale). Validity is the extent to which the score a health measure yields accurately reflects the health concept and includes face (sensible), content (comprehensive), construct (measures or correlates with a theorized health construct), and criterion validity (predicts or correlates with gold standard). Sensitivity to change (also known as responsiveness to change), an aspect of construct validity, assesses whether an instrument score changes in the right direction when underlying health construct changes; the ability of an instrument to detect clinically important change is crucial to its usefulness as an outcome measure in a clinical trial. Magnitude of the change can be assessed using effect size. Effect size is the ratio of observed change to a measure of variance (also known as signal-to-noise ratio). An effect size of 0.20 to 0.49 represents a small change; 0.50 to 0.79, a medium change; and 0.80 or greater, a large change.

Table 18-2 presents the instruments that are ready for RCTs and clinical care in patients with gout. Most of these instruments have been included in different RCTs of acute and chronic gout and endorsed by OMERACT.

Table 18-2

Proposed Outcome Measures for Clinical Trials and Clinical Practice for Acute and Chronic Gout

Instruments	Ready for RCT	Can be used in clinical practice
Health-Related Quality of Life
Short Form-36 ¶	Yes †	No
Health Assessment Questionnaire-Disability Index ¶	Yes †	Yes
Gout Impact Scale (GAQ 2.0) ¶	Yes †	No
PROMIS item banks ¶	No	Yes
Global Assessment
Patient global assessment using visual analog scale (VAS), numeric rating scale, or Likert scale ¶	Yes ∗†	Yes
Investigator global assessment using visual analog scale (VAS), numeric rating scale, or Likert scale §	Yes ∗†	Yes
Patient global assessment of response to treatment ¶	Yes ∗	Yes
Investigator global assessment of response to treatment §	Yes ∗	Yes
Patient assessment of pain using Visual Analog Scale (VAS), Numeric Rating Scale, or Likert scale ¶	Yes ∗†	Yes
Patient-reported acute flare ¶	Yes ∗†	Yes
Laboratory tests
Serum urate <6 mg/dL	Yes †	Yes
Musculoskeletal
Tender joint count §	Yes ∗†	Yes
Swollen joint count §	Yes ∗†	Yes
Tophus Measurement	Yes †	Yes
Vernier Calipers §	Yes †	Yes
Digital photography ‡	Yes †	No
Tape measure §	No	Yes

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