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To the Editor: A recent study in Heart by Edwards and colleagues found an interesting association between rheumatoid factor (RF) and ischaemic heart disease.1 In a forthcoming study we examined independently the related subject of the role of systemic inflammation in relation to clinical outcome.2 This subsequent study reports an association between systemic inflammation, as measured by C reactive protein (CRP), and all‐cause mortality (n=22982). We also found a weak association with heart disease, but the study was, we believe, statistically underpowered to evaluate this outcome properly. In light of the findings reported by Edwards and colleagues, here we report supplementary data from a subgroup of subjects from the CRP2 study, where data were available characterising RF (n=3588). The objective of this report was to characterise survival over a 4‐year period from the first CRP observation in this subgroup of subjects where RF data were also available.
Details of the data source and the general methods have been published elsewhere.2 In brief, routine data were obtained from hospital, record‐linked sources in Cardiff and the Vale of Glamorgan. A Cox proportional hazards model (CPHM) was developed using SPSS for Windows v14. We evaluated a number of potential model covariates, including age, sex, prior disease (cancer, diabetes, vascular disease), general morbidity at baseline (total days in hospital in the year before the first CRP observation) and CRP itself. RF was measured in IU/ml and included in the model as a continuous variable after logarithmic transformation.
The mean age of the 3588 evaluable subjects was 62 years and 33% were female. The CPHM of survival determined a strong association between RF and survival (hazard ratio for log RF=1.229; p=0.008). Furthermore, CRP (log transformed) was also included simultaneously in this statistical model (hazard ratio = 1.495; p<0.001) in preference to other factors such as a history of diabetes and cancer. As expected, age and being male also increased risk of death in the CPHM. Figure 11 illustrates the association between RF and all‐cause mortality.
Data from our study support the findings from the study by Edwards and colleagues, and show that RF not only predicts the likelihood of ischaemic heart disease but it also predicts the likelihood of all‐cause mortality. Furthermore, data from this subgroup of subjects showed that CRP and RF were independent risk factors for all‐cause mortality. Thus, they are likely to represent distinct inflammatory processes that increase the risk of adverse outcome.