The tube order may not seem like a big deal and may seem unnecessary to some, but it is very important to pay attention too. It also matters as to what type of needle is being used for the draw. If a butterfly needle is being used it is important to have a spit tube because with a butterfly there is air within the hose that connects the needle to the vacutainer. Its important to get this air out before filling any tubes used for patient testing. If a standard needle is being used, you typically don’t need the spit tube, but its good practice. The order still remains the same for each.
Light Blue: The typical tube for routine coagulation studies. The additive is sodium citrate (3.2% or 3.8%). Citrate is a anticoagulant which binds to calcium within the blood so the blood can’t clot. Calcium plays an important role in primary and secondary homeostasis. See my post on DIC for that information, in short it is used in the coagulation cascade. An important aspect of coagulation studies is that the light blue tube must, must be filled completely. There is a ratio of sodium citrate to whole blood and that must remain constant. The tube must be rejected if it is not filled completely.
Green or Mint Tubes: These tubes are used for chemistry studies. Often referred to as PST or plasma separator tubes. The additive in these tubes are sodium heparin, lithium heparin or ammonia heparin. The heparin, being an anticoagulant activates antithrombin, which blocks the coagulation cascade and produces a whole blood with plasma sample instead of a clotted blood and serum sample. When these tubes are centrifuged, the gel barrier moves upwards creating a barrier that separates the plasma from the red cells allowing the plasma to be aspirated directly for testing.
Gray Tube: The gray tube tops are typically used for glucose testing, ethanol levels or lactate level testing. The additive is potassium oxalate and sodium fluoride. Potassium oxalate is an anticoagulant which prevents clotting and the sodium fluoride is an anti-glycolytic which prevent the cells from using the glucose in the sample.
Lavender/Pink Tube: The lavender tube is typically used for hematological testing or for Hemoglobin A1C testing. The pink tube is used primarily for blood bank testing such as type and screen and cross-matching. The additives in the lavender and pink tubes are EDTA K2 or EDTA K3. The EDTA binds to calcium which blocks the coagulation cascade in the same way that citrate in the light blue tube does. Red cells, leukocytes, and platelets are in EDTA anticoagulated blood for 24 hours. Blood smears should be done within 3 hours of receiving the sample.
SST/Mustard Tube: Serum separator and clot activator that will separate the blood from the serum upon centrifugation. This tube is usually used to test for aldosterone, B12, ferritin and folate levels.
There are not all the different tubes that are used, but these are the most common tubes that I listed and the ones that a laboratory professional will most likely come across. Its important to understand the additive in each one to make sure that they are appropriate for the testing that needs to be done on the patient sample itself within the tube.