Any cellular element of the blood, including erythrocytes, leucocytes, and platelets.
Note: A blood cell is produced by hematopoiesis and is normally found in blood. In mammals, these fall into three general categories: red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).
Source:
PAC, 2018, 90, 1121. 'Terminology of bioanalytical methods (IUPAC Recommendations 2018)' on page 1124 (https://doi.org/10.1515/pac-2016-1120)