Vol. 14 •Issue 21 • Page 11
Q & A
Questions About Order of Draw
Q: My question concerns the order of draw for multiple tube collections. In the past, with the glass tubes, the non-additive tube was collected prior to the coagulation tube. Even if the non-additive tube is not needed, we collect a small amount of blood in this tube prior to the coagulation tube in order to get rid of any tissue-thromboplastin crossover.
Now, NCCLS guidelines for plastic tubes say the order of draw for plastic tubes is the coagulation tube before the non-additive tube. The reasoning is that the plastic non-additive tube has a clot activator added, which might interfere with the coagulation tests. Should we still collect a glass non-additive tube before the coagulation tube?
A: Although NCCLS no longer recommends that a discard tube be collected prior to a coagulation tube, there are many facilities that prefer to continue this practice. If that is the case, these facilities may opt to continue to draw discards in a glass tube. Due to the clot activator in the plastic non-additive tube (which now seems to be a misnomer), it must be filled after the sodium citrate tube, which would defeat the purpose of collecting a discard tube for tissue fluid, which could potentially interfere with coagulation test results.
Another area that may involve collecting a glass non-additive tube as a discard would be the NCCLS recommendation for drawing specimens for testing from below an IV site. The cost of tubes and glass versus plastic waste disposal may play an important role in determining whether some facilities continue to collect discard tubes in glass or additive tubes.
–Donna Kirven, BA, CPT(ASCP), CMLA, BPPVE
A: If you are using a glass tube you should continue to draw the glass non-additive tube prior to the coagulation tube. The reasoning behind the NCCLS order of draw is that the red plastic tubes contain a clot activator, which could interfere with coagulation testing if drawn before the sodium citrate tube. However, red top glass tubes do not contain any additives and therefore would not cause any cross contamination.
–Stacy Jackson, PBT(ASCP)
A: If the test is for only a PT/PTT, a 3cc blue top is sufficient for a discard tube drawing a second blue top for the test. If the lab feels that a 3cc tube is too difficult to use with the multi-draw technique, I support using a plain 5cc red top (non-additive). For multi-draw tests, the order is designed to reduce interference in specimen testing caused by inadvertently mixing additives between tubes. This can occur when blood in a tube that contains an additive makes contact with the needle that punctures the tubes, rubber top. Blood remaining within the needle may be transferred to the next tube, contaminating that tube, thus affecting test results.
EDTA causes more contamination problems than any other additive. EDTA (K3) or EDTA (NA2) cause major effects on sodium or potassium levels. Because EDTA chelates calcium and iron, a calcium or serum iron specimen should not be collected immediately after an EDTA is drawn. Both EDTA and heparin can increase the value for coagulation studies, especially PT and PTT tests. A needle contaminated by a tissue thromboplastin test can also interfere with coagulation studies.
Potassium oxalate and sodium fluoride can elevate potassium and sodium levels. Additionally, oxalate damages cell membranes and may also cause abnormal red blood cell morphology.
It’s important to remember that tests are affected by the various additives. The order of draw eliminates the potential of these false testing results. Each lab should do its own quality assurance study on the types of instrumentation used against the additives of the tubes used to draw the specimens, to determine their particular order of draw policy.
–Rick Gregory, CPT(NPA), ISCLT
This Week’s Q&A Panel
Donna Kirven is phlebotomy education and training coordinator at John Muir Medical Center, Walnut Creek, CA.
Stacy Jackson is staff development/safety coordinator at University Medical Center, Clinical Pathology Department, Lubbock, Texas.
Rick Gregory is CEO of SCPT.com, a Southern California Phlebotomy Training Web site. He has worked in health care as a phlebotomist and lab manager for 17 years.