Which tube should be drawn last if testing for crossmatch?

In phlebotomy, the order of draw is crucial to prevent contamination of samples and ensure accurate test results. When conducting a crossmatch, the preferred tube to be drawn last is the red top tube.

The red top tube is typically used for serum tests, including crossmatching blood for transfusions. Drawing it last minimizes the risk of any additives from the other tubes contaminating the specimen, which could compromise the test results. Since the crossmatch is a critical procedure that requires high accuracy, using a tube that does not contain any additives is essential.

The other tubes mentioned, such as the blue, gold, and purple top tubes, contain various additives that can interfere with serum analysis. For example, blue top tubes contain sodium citrate, which is used for coagulation studies. Gold top tubes (which may contain a gel separator) are often used for chemistry tests, and purple top tubes contain EDTA, which is used for hematology tests. If any of these tubes were drawn after the red top tube, their additives could potentially compromise the integrity of the serum sample needed for crossmatching, making it crucial to follow the appropriate order of draw.

In summary, the red top tube is drawn last when performing a crossmatch because it is