The other expert is correct that this is not a typical finding on a CBC. There are some labs that will perform a modification of the CBC in which only a partial differential is performed. The standard CBC differential will count the neutrophils, lymphocytes, monocytes, eosinophils, and basophils, which are distinguished based upon their appearance. There also can be some atypical cells that would be specifically identified, if present. The partial differential counts based on the size of the white cells and generates results for the neutrophils and lymphocytes, as they have distinctive sizes, but the remaining types of cells are similar in size, so are grouped together in the "mid" result (short for midsize). Since there are several types of white cells that are included in the "mid" range, it is difficult to say what is causing the number to be elevated. For example, an elevation in the number of monocytes can occur in a variety of infections or inflammatory conditions, but an increase in eosinophils can occur from allergies or parasitic disease. Usually, the next step if the mid number is XXXXX is to perform a complete CBC so that the exact count of the various white cells can be determined, which will then guide further evaluation.