Which tubes are sent to Microbiology for testing?

The correct choice is the blood culture tubes because they are specifically designed to detect the presence of microorganisms in a patient's blood. These tubes contain culture media that promote the growth of bacteria or fungi, allowing healthcare professionals to identify infections that may be present in the bloodstream. Blood cultures are a critical tool in diagnosing septicemia and other systemic infections.

In the context of the other options, plain red tubes and SST (serum separator tubes) are used for collecting serum samples for various chemistry and serology tests, but they do not support the growth of microorganisms and thus are not utilized in microbiological testing. The pink tube primarily serves for blood bank testing and is not intended for microbiology studies. Therefore, blood culture tubes are uniquely suited for the specific needs of microbiological analysis.