Compositions, systems, and methods comprising circulating endothelial cells (CECs) are provided. The compositions described herein utilize isolated CECs, including compositions in a form that allows analysis of the CECs. The systems described herein utilize isolated CECs and an analytical tool or an output from an analytical tool. The methods described herein are related to the use of isolated CECs and analytical tools for providing information, to a health care provider or the CEC donor, that is relevant to the cardiovascular health of the CEC donor. Thus, the compositions, systems and methods described herein involve both a transformation (e.g., non-isolated CECs to isolated CECs, or isolated CECs to analyzed CECs) and a machine (e.g., isolation tools and analytical tools).