What is high mono on blood test mean? Howard, welcome to Answers! The term for a high blood circulating number of the white blood cells named monocytes is monocytosis. Monocytosis is an increase in the number of monocytes in the peripheral bloodstream. Various limits are given (e.g., a total number in excess of 800/mm3, regardless of the percentage, or a total greater than 8% with the total number less than 800).