What is the correct order of draw for a CBC (lavender top), comprehensive metabolic panel (SST), PT (light blue top), and a set of blood cultures?

The correct order of draw for these blood collection tubes is critical for ensuring accurate test results and preventing cross-contamination of additives found in the tubes. Blood cultures are always drawn first to minimize the risk of contamination, as they are particularly sensitive to any additives that might be in other tubes.

Following blood cultures, the light blue top tube, which is used for coagulation studies such as PT (prothrombin time), should also come next. This is because the additive in the light blue tube, which is sodium citrate, requires a specific ratio with blood to ensure accurate testing.

Next in the order of draw is the SST (serum separator tube), which contains a gel separator and is used for various metabolic panels, including the comprehensive metabolic panel. Finally, the lavender top tube, which is used for complete blood counts (CBC), comes last. The EDTA in the lavender tube can interfere with other tests if drawn earlier, particularly those involving serum or plasma obtained from the SST.

Thus, the sequence of blood cultures, light blue top tube, SST, and then lavender top tube appropriately adheres to the standard guidelines for the order of draw, ensuring reliable and accurate laboratory results.