A module for staging sample tubes and mixing the samples contained in the sample tubes for an automated clinical analyzer. In one embodiment, this module comprises a mixing drum, which is capable of mixing the contents of a sample tube in an end-over-end manner. The mixing drum is capable of mixing samples in the sample tubes without separating the solid components of the sample, e.g., red blood cells from the liquid components of the sample, e.g., plasma. A device for elevating the sample tube in the sample tube carrier can be used to enable the cap of the sample tube to be punctured by a piercing element in a piercing assembly. After the cap of the sample tube is punctured, a probe for aspirating the sample from said sample tube can obtain the sample in the receptacle of the sample tube through a bore in the piercing element. The piercing assembly can include a resiliently biased element for ejecting the sample tube from the piercing assembly.