Which of the following is NOT detected in an unmixed specimen?

In an unmixed urine specimen, it is important to understand the properties of the components typically found within it. Red blood cells (RBCs) can settle at the bottom of a specimen if it is left undisturbed, making it less likely to be evenly distributed or detected without mixing. In contrast, white blood cells (WBCs), ketones, and contaminants are distributed throughout the urine sample to a greater extent, making them more detectable in an unmixed state.

WBCs may be suspended evenly enough to be counted in an unmixed sample, as they do not settle as readily as RBCs. Ketones, which can be present in urine in various concentrations, tend to remain mixed within the fluid. Contaminants can also be distributed throughout the sample as they often come from external sources or may dissolve in the urine.

Therefore, the nature of RBCs allows for significant settling, leading to their reduced visibility and detection in an unmixed specimen compared to the other components listed.