Phlebotomy and Specimen Collection: Order of Draw and Labeling
Core concepts
Specimen questions test order, technique, and identification. Memorize the order of draw: blood culture (or sterile tube first), then light blue (sodium citrate, coagulation), then serum tubes with or without clot activator (red/gold), then green (heparin), then lavender (EDTA), then gray (oxalate/fluoride). The reason is additive carryover: EDTA and heparin can contaminate later tubes and skew results. Light blue must be filled to the indicated line because the blood-to-additive ratio drives coagulation results. Gently invert tubes the number of times the additive requires; never shake, which hemolyzes the sample.
Know common tests by tube: coagulation studies in light blue, chemistry in serum or heparin tubes, hematology (CBC) in lavender, glucose in gray. Capillary collection uses the side of the fingertip, wipe away the first drop, and avoid squeezing hard. Venipuncture sites to avoid: the arm with an IV, a mastectomy arm with lymph node removal, edematous or scarred areas, and hematomas.
Traps
Questions bait you with a wrong order (putting lavender before light blue) or with a short-filled light-blue tube that "looks fine." Label at the bedside, never in advance, and never label a tube for another patient. Do not use a tourniquet longer than about one minute; prolonged tourniquet time falsely raises potassium and other values. Never draw above an IV site or from an arm with a dialysis fistula.
Worked example
You need a CBC and a coagulation panel. Rule of thumb: light blue first, then lavender. If you draw lavender first, the EDTA carryover can falsely lower calcium and alter coagulation results.
Rule of thumb
"Sterile, blue, red/gold, green, lavender, gray" keeps additive contamination in the right direction.