American Medical Certification Association (AMCA) Phlebotomy Practice Exam

If an EDTA tube is used before a serum tube, it could cause cross-contamination and result in what?

1. High sodium levels

2. High potassium or a false low calcium value

3. False positive for anemia

4. Fluid overload

The correct answer is: High potassium or a false low calcium value

Using an EDTA tube before a serum tube can lead to cross-contamination, primarily because EDTA is an anticoagulant that binds calcium in the blood. If blood collected in an EDTA tube is then transferred to a serum tube, the presence of EDTA can interfere with several biochemical tests. Specifically, it can cause elevated potassium levels due to the release of potassium from cells that may occur during the collection process. Additionally, the calcium-binding properties of EDTA can result in a falsely low measurement of calcium in serum specimens, as the EDTA effectively removes calcium from the sample. Understanding this process highlights the importance of following the proper order of draw in phlebotomy. This order is designed to prevent such cross-contamination and ensure accurate test results. In contrast, the other options do not accurately reflect the consequences of drawing an EDTA tube before a serum tube in the context of biochemical testing.