Medical Technology Licensure Examination (MTLE) Practice Exam

In the order of draw for blood collection, which type of tube follows after light blue and red tubes?

1. EDTA tube

2. SST tube

3. Lavender tube

4. Green tube

The correct answer is: SST tube

In the order of draw for blood collection, the tube that follows the light blue and red tubes is the serum separator tube (SST). The rationale behind this order revolves around the potential for additive carryover from one tube to the next, which could affect test results. Light blue tubes contain sodium citrate, which is an anticoagulant, and are typically used for coagulation tests. Following the light blue tube, red tubes are often used for serum collection without any additives. After collecting from these tubes, the SST, which contains a gel that separates serum from the cells upon centrifugation, is drawn next. This placement ensures that any potential contamination from anticoagulants in the previous tubes does not interfere with tests performed on the serum. The other options, such as EDTA tubes (lavender), which contain an anticoagulant, or the green tube, which also has an anticoagulant (heparin), are drawn later in the process to prevent any interference with the tests that require the serum collected in the SST. Thus, the sequence is crucial to maintaining the integrity of the samples and obtaining accurate lab results.