Background
The burden of non-communicable diseases (NCDs) is rising rapidly in middle-income countries (MICs), where NCDs are often undiagnosed, untreated and uncontrolled. How comorbidity impacts diagnosis, treatment, and control of NCDs is an emerging area of research inquiry and have important clinical implications as highlighted in the recent National Institute for Health and Care Excellence guidelines for treating patients suffering from multiple NCDs. This is the first study to examine the association between increasing numbers of comorbidities with being undiagnosed, untreated, and uncontrolled for NCDs, in 6 large MICs.

Methods
Cross-sectional analysis of the World Health Organisation Study of Global Ageing and Adult Health (WHO SAGE) Wave 1 (2007–10), which consisted of adults aged ≥18 years from 6 populous MICs, including China, Ghana, India, Mexico, Russia and South Africa (overall n = 41, 557).

Results
A higher number of comorbidities was associated with better odds of diagnosis for hypertension, angina, and arthritis, and higher odds of having treatment for hypertension and angina. However, more comorbidities were associated with increased odds of uncontrolled hypertension, angina, arthritis, and asthma. Comorbidity with concordant conditions was associated with improved diagnosis and treatment of hypertension and angina.

Conclusion
Patients with more comorbidities have better diagnosis of chronic conditions, but this does not translate into better management and control of these conditions. Patients with multiple NCDs are high users of health services and are at an increased risk of adverse health outcomes. Hence, improving their access to care is a priority for healthcare systems.