Health care utilization in patients with gout: a prospective multicenter cohort study

BACKGROUND

All published studies of health care utilization in gout have been cross-sectional to date, and most used a patient-reported diagnosis of gout. Our objective was to assess health care utilization and its predictors in patients with physician-confirmed gout in a prospective cohort study.

METHODS

In a multi-center prospective cohort study of U.S. veterans with rheumatologist-confirmed gout (N = 186; two centers), we assessed patient self-reported overall and gout-specific health care utilization with the Gout Assessment Questionnaire (GAQ) every 3-months for a 9-month period. Comparisons were made using the student's t test or the chi-square, Wilcoxon rank sum test or Fisher exact test, as appropriate. Mixed effects Poisson regression was used to assess potential correlates of gout-related health care utilization.

RESULTS

Mean age was 64.6 years, 98% were men, 13% Hispanic or Latino, 32% were African-American, 6% did not graduate high school, mean serum urate was 8.3 and mean Deyo-Charlson score was 3.1. During the past year, mean gout-related visits were as follows: rheumatologist, 1.5; primary care physician, 2 visits; ≥1 inpatient visits, 7%; ≥1 ER visits, 26%; and urgent care/walk-in visit, 33%. In longitudinal analyses, African-American race and gout flares in the last 3 months were associated with significantly higher rate ratio of gout-related outpatient visits. African-American race and lack of college education were associated with significantly higher rate ratio for gout-related urgent visits and overnight stays.

CONCLUSIONS

African-American race and recent gout flares were associated with higher outpatient utilization and African-American race and no college education with higher urgent or inpatient utilization. Future studies should examine whether modifiable predictors of utilization can be targeted to reduce healthcare utilization in patients with gout.

Racial differences in health-related quality of life and functional ability in patients with gout

OBJECTIVE

To compare the health-related quality of life (HRQOL) and the functional ability by race in patients with gout.

METHODS

In a 9-month prospective cohort multicentre study, patients with gout self-reported race, dichotomized as Caucasian or African American (others excluded). We calculated HRQOL/function scores adjusted for age, study site and college education for Short Form-36 (SF-36; generic HRQOL), Gout Impact Scale (GIS; disease-specific HRQOL) and HAQ-disability index (HAQ-DI; functional ability). Longitudinally adjusted scores were computed using multivariable mixed-effect regression models with a random patient effect and fixed sequential visit effect (3-monthly visits).

RESULTS

Compared with Caucasians (n = 107), African Americans (n = 60) with gout were younger (61.1 vs 67.3 years) and had higher median baseline serum urate (9.0 vs 7.9 mg/dl) (P < 0.01). African Americans with gout had worse HRQOL scores on three SF-36 domains, the mental component summary (MCS) and two of the five GIS scales than Caucasians [mean (se); P ⩽ 0.02 for all]: SF-36 mental health, 39.7 (1.1) vs 45.2 (0.9); SF-36 role emotional, 42.1 (4.2) vs 51.4 (4.2); SF-36 social functioning, 36.0 (1.1) vs 40.0 (0.9) (P = 0.04); SF-36 MCS, 43.2 (3.1) vs 50.0 (3.2); GIS unmet treatment need, 37.6 (1.6) vs 31.5 (1.4); and GIS concern during attacks, 53.3 (3.7) vs 47.4 (3.7). Differences between the respective HAQ-DI total scores were not statistically significant; 0.98 (0.1) vs 0.80 (1.0) (P = 0.11). Racial differences in SF-36 mental health, role emotional and MCS scales exceeded, and for HAQ-DI approached, the minimal clinically important difference thresholds.

CONCLUSIONS

African Americans with gout have significantly worse HRQOL compared with Caucasians. Further research is necessary in the form of studies targeted at African Americans on how best to improve these outcomes.

Diagnosis of rheumatoid arthritis. Medical and laboratory aspects

The diagnosis of rheumatoid arthritis (RA) is largely dependent on the existence of a characteristic pattern of clinical symptoms and signs that must be present for at least six weeks. Early morning joint stiffness and symmetric polyarticular inflammation, particularly in the metacarpophalangeal, proximal interphalangeal, wrist, and metatarsophalangeal joints, are typical of the disease. Extraarticular disease, including rheumatoid nodules, is usually associated with severe and well-established arthritis, and occular, pulmonary, cardiac, neurologic, and vasculitic involvement can be a considerable source of morbidity. Serologic testing for rheumatoid factor (RF) is helpful in confirming the diagnosis since 80% of patients are seropositive, but RFs are expressed in many other disease states. Expression of multiple RF isotypes differentiates RA from other populations. Erythrocyte sedimentation rates, C-reactive protein levels, circulating immune complexes, and platelet counts are often elevated in RA and serve as indicators of disease activity.

Human IgG anti-F(ab')2 antibodies possess rheumatoid factor activity

Individual preparations of affinity purified anti-F(ab')2 antibodies and anti-Fc antibodies isolated from the sera of patients with rheumatoid arthritis (RA), were examined for reactivity with the Fab and Fc fragments of human IgG. Western blot assays demonstrated specific interaction of affinity-purified anti-Fab antibodies with both Fab and Fc molecules. Approximately one-half of the anti-Fab antibody preparations studied contained IgG antibodies reactive with Fab and Fc fragments in ELISA, suggesting the existence of naturally occurring epibody-like autoantibodies in these patients. Thirteen of 14 affinity-purified anti-Fc antibody preparations contained IgG cross-reactive with Fab molecules in ELISA. Double-adsorption assays on affinity columns demonstrated that a minimum of 14%, and possibly as much as 50%, of the IgG anti-Fab antibodies reacted with the Fc of IgG. Conversely, a minimum of 12%, and possibly as much as 70%, of the IgG anti-Fc antibodies reacted with IgG Fab molecules. Anti-Fab antibodies isolated from non-RA individuals also exhibited anti-Fc reactivity in ELISA, demonstrating the presence of these dual-reactive antibodies in other autoimmune and normal individuals. These studies establish the presence of naturally occurring IgG autoantibodies reactive with both the Fab and Fc fragments of human IgG. Their existence emphasizes the potential of anti-immunoglobulin antibodies to recognize a multiplicity of antigens, possibly including other members of the immunoglobulin supergene family.

Serum IgG4 anti-Fab antibodies in rheumatoid arthritis are constitutively expressed

IgG4 comprises a significant proportion of the total anti-Fab antibody (aFABA) response in many but not all patients with rheumatoid arthritis (RA). Analyses of the dynamics of IgG aFABA subclass expression in 11 RA patients for periods of up to 11 months demonstrated that IgG4 aFABA was restricted to 6 of the 11 RA patients' sera initially studied and comprised approximately 25% (or more) of the total IgG aFABA response. Quantities of IgG4 aFABA in subsequent, serially obtained serum samples from these patients remained stable throughout the study period, whereas the remaining RA patients whose initial sera possessed small quantities of serum IgG4 aFABA failed to generate any augmented IgG4 aFABA response during the study. Elevated expression of IgG4 aFABA did not appear to be a consequence of a generalized polyclonal gammopathy or a generalized increase in autoantibody expression, though patients with higher total IgG4 serum levels expressed significantly greater quantities of IgG4 aFABA. These results indicate that the differential expression of IgG4 aFABA among RA patients reflects constitutive production within a subset of RA patients in whom IgG4 appears to comprise a significant proportion of the total IgG aFABA response.

Recognition by anti-Fab antibodies in rheumatoid arthritis of structure(s) widely distributed on human Fab molecules

Anti-Fab antibodies (aFABA) of restricted clonality and acidic spectrotypes were isolated from the sera of patients with rheumatoid arthritis (RA). These aFABA reacted with multiple populations of pooled human Fab molecules, which had been charge separated by chromatofocusing techniques (CF), indicating that the structures recognized by these aFABA were present on a polyclonal population of Fab molecules. The structures were also widely distributed among the Fab repertoires of normal individuals, as well as individual autologous and heterologous RA patients. Thus, the aFABA did not appear to recognize highly restricted epitope(s), i.e. a private idiotope, limited in its expression to RA individuals. The determinants of the Fab molecules recognized by affinity purified aFABA could be defined by linear and/or conformational structures, depending upon the individual from which the aFABA were isolated. Additionally, some of the affinity purified aFABA also reacted with Fc fragments, suggesting the presence of epibody-like autoantibodies in this population. Lastly, size analysis of the circulating IgG4 aFABA complexes indicated that these autoantibodies were not complexed with intact IgG, but rather with a molecule of 40-60 kDa, further suggesting the potential for these autoantibodies to react with multiple antigens.

Anti-Fab antibodies in humans. Predominance of minor immunoglobulin G subclasses in rheumatoid arthritis

Isoelectric focusing analyses of sera from patients with rheumatoid arthritis (RA) demonstrate two populations of antibodies directed against the Fab portion of pooled human IgG. One population is composed of polyclonal alkaline anti-Fab antibodies (alpha FABA) and the other, acidic alpha FABA which are more clonally restricted. In this study we have identified the immunoglobulin classes and subclasses of these antibodies in RA sera. Enzyme-linked immunosorbent assays (ELISA) demonstrated alpha FABA in RA sera to be predominantly IgG. A large portion of IgG alpha FABA existed as immune complexes, inasmuch as dialysis of RA sera against 6 M urea before ELISA analysis was necessary for maximal detection of alpha FABA activity. Chromatofocusing of RA sera isolated alpha FABA of different charges and revealed the acidic clonally restricted alpha FABA to be IgG4 and IgG3, whereas the polyclonal alkaline group contained IgG1, IgG2, and IgG3. Overall, acidic IgG3 and IgG4 comprised 70% of IgG alpha FABA, and high levels of IgG4 were seen in most RA sera. When alpha FABA were elevated in normal sera, they were primarily of the IgG4 subclass, and also existed as immune complexes. Serum anti-Fab activity was removed by adsorption of sera with Fab fragments. Anti-Fab antibodies of both kappa and lambda light-chain types were present in RA sera, and F(ab')2 fragments of RA serum immunoglobulin were found to possess anti-Fab activity. These studies indicate that alpha FABA in RA sera are limited to the IgG class, and that most of these antibodies exist as immune complexes and display clonal and minor IgG subclass restriction.

Subclasses of human IgG anti-Fab antibodies: parameters for optimum detection

In this study we have defined the parameters needed for the optimum detection of anti-Fab antibodies in the serum of patients with rheumatoid arthritis. We have found that the majority of the anti-Fab antibodies are of the IgG3 and IgG4 subclasses which were not optimally detected using polyclonal heterologous anti-human IgG antisera; subclass-specific antibodies instead were needed. Additionally we determined that dissociation of circulating immune complexes by dialysis against urea for 3-7 days was also needed for the detection of these antibodies. Lastly we have shown that the dissociated complexes can recombine with their target Fab molecules, and therefore separation of the anti-Fab antibodies from the other immunoglobulins by chromatofocusing may enhance the detection of these antibodies. When the above conditions were fulfilled it was determined that IgG anti-Fab antibodies could be detected in rheumatoid arthritis and normal sera and that acidic IgG3 and IgG4 subclasses predominated. However, IgG3 levels were 10.5-fold higher in rheumatoid arthritis sera (p less than 0.05) and IgG4 levels 5-fold higher (p less than 0.01) than in normal sera.

Clonally restricted anti-IgG antibodies in rheumatoid arthritis

Clonally restricted anti-IgG antibodies were detected, by isoelectric focusing (IEF) and chromatofocusing techniques, in the sera of patients with rheumatoid arthritis (RA). Anti-Fab antibodies were predominantly acidic proteins with isoelectric points of 4.5-6.5 and displayed restricted spectrotype patterns. Proteins reactive with the Fc portion of IgG showed polyclonal spectrotype patterns with alkaline pI of 7.5-9.0. A limited array of anti-Fab spectrotypes was consistently detected in RA sera when analyzed by IEF on 6M urea gels. Additional anti-Fab antibody bands were detected when the RA sera were dialyzed against 4-6M urea prior to IEF analysis, indicating that some anti-Fab antibodies exist in a complexed form in serum. Under these dissociating conditions, anti-Fab antibodies could also be detected in normal subjects, but the spectrotype patterns were more restricted than those in RA sera. Because anti-Fab antibodies may regulate normal immune responses, the increased quantity of clonally restricted anti-Fab antibodies in RA may indicate an abnormality of this immunoregulation.