There are many factors that must be taken into consideration when collecting an adequate blood sample for laboratory testing, but one of the most important is the order of draw. Order of draw is essential in avoiding cross contamination from additives of one tube to the next. Cross contamination, depending on the tests ordered, could cause seriously erroneous results, improper patient treatment and possibly death.
While most blood collections (straight venipuncture vs. winged infusion collection or skin puncture) should follow the same order of draw according to CLSI recommendation, there are some differences that need to be remembered and taken into consideration. Order of draw that should be followed is: blood cultures (sterile collections), light blue (sodium citrate), black (sodium citrate ESR), red (with or without clot activator), SST (separator), green (heparin or PST), lavender (EDTA), gray (sodium fluoride/ potassium oxalate-collected after the lavender tube in order to avoid distortion of cell morphology as well as the destruction of enzymes in chemistry analysis), royal blue (trace elements).
For a winged infusion draw, a "dummy" tube must be drawn first to negate the dead air space in the tubing (NOTE: A red top or SST should never be used as a discard tube if coagulation studies are ordered as these tubes contain a clot activator). When collecting via skin puncture, the following should be followed: blood gases, lavender, other additive tubes, non-additive tubes (to minimize clotting).
Most, if not all, laboratories have a form of a test catalog. A good, clear, test catalog will give you all of the information needed to collect an adequate specimen. Information you might find in such a catalog would include test name, test code, processing instructions, transport temperature, stability limit, reference ranges, methodology, synonyms and, most importantly, tube type/collection container that would include a picture of the specific tube that is needed.
In most cases; for example, there are tests that we would recommend be collected in a dark blue top tube, which is fine, but which type of dark blue top tube? No additive? K2 EDTA? Or dark blue Hemogard FSP collection container? The test catalog is a great reference to get an idea of what tubes are needed, specifically so the proper order of draw can be followed. There are also the same possibilities with tests that need to be collected in green top tubes (whole blood or plasma separator), or light yellow (SPS or ACD A or B solutions).
In addition to correct order of draw, there are a few steps that must be taken in order to ensure proper mixing of the additive in the tube. There are a specific number of times a tube should be inverted (gently rotating the tube from left to right). Light blue: 3-4 times, red/SST: 5-6 times, green/PST: 8-10 times, lavender: 8-10 times. Insufficient mixing can result in inaccurate test results, and cause the patient to be re-drawn.
Proper fill rates need to be followed, most specifically for coagulation studies. The proper rate for a light blue tube is 9:1 in order to avoid prolonged clotting times; proper specimen clotting, which for a SST is 30 minutes in the upright position; and lastly, specimen processing and centrifugation. To ensure the specimen is accurately spun and processed, in most cases, the tubes must be spun for 10 minutes at 3000 RPM.
Terri A. McElhattan is program director/instructor, Geisinger School of Phlebotomy; and Kristine M. Evans is team leader, Off-Site Phlebotomy, Geisinger Medical Laboratories, Danville, Pa.