A Rainbow of a Different Sort

In life, what is sometimes normal to one person may be completely new or intriguing to another. Having worked in health care for more than thirty-five years as a hospital lab tech, the different color tubes being draw seem common place and ordinary. However, to someone getting blood work performed due to sickness or a wellness checkup, the rainbow of tubes being drawn may arouse questions and curiosity.

Vacuum tubes for collecting blood samples were invented in 1947 by Joseph Kleiner. It was revolutionary in that it allowed blood to be collected directly into the tubes, thus preventing the blood from being exposed to air or other contaminates. This groundbreaking innovation changed the future of blood testing dramatically, spawning new tests, and enhanced healthcare.

 

So, why all the colors? Each tube contains a different additive that allows testing of different analytes.

The familiar purple or lavender tube is one of the most common. It contains EDTA which acts as an anticoagulant, binding the calcium ions and interrupting the clotting of the blood sample. It is used for most hematology procedures, assessing the CBC (complete blood count). It allows for the measurement of the number of red and white blood cells along with platelets, and also the total quantity of blood, shown as hemoglobin and hematocrit. If you have a fever, malaise, fatigue or potential blood loss, expect a lavender tube to be drawn.

The green top tube is also a common collection choice as it contains lithium heparin and a gel separator used for the collection of heparinized plasma for routine chemistry tests.  Heparin works by preventing certain cofactors, namely thrombin and fibrin, from working correctly thus preventing clotting.  The tube is spun down with a centrifuge and the liquid part of the blood (plasma) is used for testing.  If you are having issues with thyroid, heart, liver, pancreas, kidneys or diabetes, the green tube will most likely be drawn.  

The blue tube is utilized for clotting factors. The sodium citrate in the tube prevents coagulation by binding ionized calcium, which is required in clot formation. During testing, these factors are added back in and measured to determine how quickly the blood clots. Patients on blood thinners will have the blue tube drawn to determine what level of medication they need to be on.

    

The red, marbled orange and yellow tubes are all similar in that they do not have additives in the tube. When the blood is drawn in these tubes it is allowed to clot. It is then spun down and the resulting liquid portion called serum is used for testing. Many specialized tests such as antibody testing, hormones, and some medications can only be done on serum. If your doctor has ordered these tests, the red tube may be in order.

The indigo tube is used to measure trace metals such as lead, mercury, and arsenic.  It, along with a few other color tubes such a grey and tan are rarely used yet could be on the draw list if certain tests were ordered by the physician.  

Getting blood work performed is often not a desired procedure, and all the color tubes can be confusing.  Therefore, a little information about a rainbow of another sort may make your experience a little better and aid in understanding the reason for the multicolored array of receptacles used in the procurement of your blood.    

~Mark