Final answer:
To determine a patient's sodium level, a phlebotomy technician should select a collection tube with a top color of yellow, known as a serum separator tube (SST), which contains a gel to separate the blood cells from the serum during centrifugation.
Step-by-step explanation:
The phlebotomy technician should select a collection tube with a top color of yellow to obtain a blood specimen for determining a patient's sodium level. The yellow top tube is called a serum separator tube (SST) and contains a gel that separates the blood cells from the serum during the centrifugation process. This allows for the collection of clear serum, which is needed for the sodium level analysis.