Various embodiments of the present invention provide, for example, a system and method for automatically adjusting the inoculum level of a sample. Certain embodiments of the present invention may measure a concentration of particles present in a preliminary sample using a sensor device and determine an amount of diluent to be added to or removed from a sample container to prepare a sample having a selected concentration of particles, corresponding to a selected inoculum level. Embodiments of the present invention may also automatically add or remove the diluent using an automated fluidics system so as to prepare a sample having the selected particle concentration. Once the selected particle concentration is achieved and verified, some embodiments may also remove at least a portion of the sample from the sample container such that the container contains a selected volume of the sample.