Age, sex, and socioeconomic differences in multimorbidity measured in four ways: UK primary care cross-sectional analysis

Background: Multimorbidity poses major challenges to healthcare systems worldwide. Definitions with cut-offs of more than ≥2 long-term conditions (LTCs) might better capture populations with complexity but are not standardised.

Aim: This study examined variation in prevalence using different definitions of multimorbidity.

Design and setting: Cross-sectional study of 1168620 people in England.

Methods: Comparison of multimorbidity prevalence using four definitions: MM2+ (≥2 LTCs), MM3+ (≥3 LTCs), MM3+ from 3+ (≥3 LTCs from ≥3 ICD-10 chapters), and mental-physical MM (≥2 LTCs where ≥1 mental and ≥1 physical). Logistic regression was used to examine patient characteristics associated with multimorbidity under all four definitions.

Results: MM2+ was most common (40.4%) followed by MM3+ (27.5%), MM3+ from 3+ (22.6%), and mental-physical MM (18.9%). MM2+, MM3+, and MM3+ from 3+ were strongly associated with oldest age (aOR 58.09 [56.13-60.14]), aOR 77.69 [75.33-80.12]), and aOR 102.06 [98.61-105.65] respectively), but mental-physical MM was much less strongly associated (aOR 4.32 [4.21-4.43]). People in the most deprived decile had equivalent rates of multimorbidity at a younger age than those in the least deprived. This was most marked in mental-physical MM at 40-45 years younger, followed by MM2+ at 15-20 years, and MM3+ and MM3+ from 3+ at 10-15 years. Women had higher prevalence of multimorbidity under all definitions, which was most marked for mental-physical MM.

Conclusion: Estimated prevalence of multimorbidity depends on the definition used, and associations with age, sex, and socioeconomic position vary between definitions. Applicable multimorbidity research requires consistency of definitions across studies.