Three terms are commonly used interchangeably to identify vulnerable older adults: comorbidity, or multiple chronic conditions, frailty, and disability. However, in geriatric medicine, there is a growing consensus that these are distinct clinical entities that are causally related. Each, individually, occurs frequently and has high import clinically. This article provides a narrative review of current understanding of the definitions and distinguishing characteristics of each of these conditions, including their clinical relevance and distinct prevention and therapeutic issues, and how they are related. Review of the current state of published knowledge is supplemented by targeted analyses in selected areas where no current published data exists. Overall, the goal of this article is to provide a basis for distinguishing between these three important clinical conditions in older adults and showing how use of separate, distinct definitions of each can improve our understanding of the problems affecting older patients and lead to development of improved strategies for diagnosis, care, research, and medical education in this area.

The risk of an avoidable inpatient admission or a preventable complication in an inpatient setting increases dramatically with the number of chronic conditions. Better primary care, especially coordination of care, could reduce avoidable hospitalization rates, especially for individuals with multiple chronic conditions.

Noncardiac comorbidities are highly prevalent in older patients with CHF and strongly associate with adverse clinical outcomes. Cardiologists and other providers routinely caring for older patients with CHF may improve outcomes in this high-risk population by better recognizing non-CHF conditions, which may complicate traditional CHF management strategies.

In a nationally representative sample, higher Medicare expenditures associated with a diagnosis of dementia are in large part due to increased hospitalization. Further study is needed into the factors associated with high rates of hospitalization in dementia patients including aspects of ambulatory management that may be improved.

The amount of NIH funding for research on a disease is associated with the burden of the disease; however, different measures of the burden of disease may yield different conclusions about the appropriateness of disease-specific funding levels.