Comorbidity is common. National Institute for Health and Clinical Excellence (NICE) guidelines have been created to make best use of resources to improve patients' quality of life but do not currently take account of comorbidity. The effect of multiple chronic conditions with regard to health-related quality of life (HRQoL) is poorly researched. Criticisms of previous research have been due to patient-defined chronic conditions, lack of quantification of the effects of confounding factors, selection of affected patients only, small sample sizes, and upper age limits. This study aims to address these issues, looking into the impact of combinations of chronic conditions on HRQoL. Participants filled in a questionnaire containing general health information, specific respiratory questions, and the EQ-5D measure of HRQoL. The questionnaires were then matched up to their GP records to obtain their disease status for six common chronic diseases (asthma, chronic obstructive pulmonary disease, ischaemic heart disease, hypertension, diabetes, and cerebrovascular disease). Data from a mailed questionnaire were analysed from 5169 patients aged >16 years from two general practices in Wythenshawe, Manchester in 2004. Completion of the questionnaire was taken to indicate consent to participate. Significant correlations were found between a lower HRQoL and increasing numbers of chronic conditions (P<0.001), increasing age, possible obstructive airway disease, lack of higher education, smoking, and female sex. These all remained significant following regression, except for sex, with number of chronic conditions being a strong predictor of the weighted health state index score, EQ-5D(index) (coefficient = -0.079, P<0.001). Increasing numbers of chronic conditions have a strong negative effect on HRQoL.
