Many patients having their blood drawn notice the Phlebotomist uses several different blood collection tubes, each bearing a different colored top. These blood collections tubes, part of the Phlebotomist’s daily supplies, play an important part in the blood collection process.
Known as a vacutainer tube, the blood collection tubes were first developed in the late 1940’s by Joseph Kleiner. Originally all glass, now only certain types of blood collection tubes remain glass. Others are plastic. Currently, BD (Becton and Dickinson) manufactures the vacutainers used by most healthcare facilities.
Test tubes are covered in color-coded caps to differentiate between them. The Phlebotomist will use specific tubes when drawing blood for tests ordered by the Physician. Certain blood tests require the collected blood to be mixed with an anticoagulant. An anticoagulant prevents blood, which normally forms clots, to remain in a liquid state. Some blood collection tubes contain these additives which mix with the collected blood. Other tests do not require an additive. The cap color on each test tube indicates any additives that are contained within the tube as well as what tests that particular tube is used for.
Anticoagulant Blood Tests
Certain blood tests require anticoagulants to be added. These anticoagulants prevent the blood from clotting. The additives bind to ions which prevent proteins in the blood from clotting, their normal function.
Light Blue – This tube contains a certain amount of citrate which is an anticoagulant. This is used for coagulation assays. The tube must be filled because citrate dilutes the blood.
Light green / green – This tube contains sodium heparin (or lithium heparin).This is used for plasma determinations for chemistry such as urea.
Lavender- This tube contains EDTA (potassium salt), a powerful anticoagulant. This is used for a CBC, complete blood count, as well as blood films. This tube is also used for blood bank type and screen, or for whole blood analysis.
Pink (Blood Bank EDTA) – This tube contains EDTA (potassium salt). This is used for cross matching, for use in a blood bank.
Gray – This tube contains oxalate (an anticoagulant) and fluoride, which prevents enzymes from working.
Royal Blue – This tube contains sodium heparin (anticoagulant) as well as EDTA. This is used for trace metal analysis of a patient’s blood.
Blood Collection Tubes
Neither coagulant / anticoagulant
Black –This tube goes to the hematology department. This is used for Erythrocyte Sedimentation Rate, commonly referred to as a ‘sed rate.’ This is used to measure the rate at which red blood cells settle to the bottom of the test tube within one hour. The rate helps to determine any inflammatory processes with the patient.
Red (glass)-This contains no additives. This is used for drug testing as well as antibodies.
Light Yellow –This contains SPS (sodium poly sulfonate) or acid citrate dextrose. This is used for blood cultures, DNA testing, paternity testing, and blood bank studies.
Light Tan –If glass, this contains sodium heparin. If plastic, this contains K2EDTA. This is used to determine lead. The tubes are certified lead free.
White – This contains EDTA as well as a gel additive. This is used for molecular diagnostic testing such as branched DNA amplification.
Coagulant Blood Tests
Before a surgical procedure, a patient’s clotting ability is usually tested. This ensures the patient will not continue to bleed after the surgery. Patients that are on blood thinning medications, such as those with a history of heart attack or stroke, will also have their ability to clot checked.
Gold or Red/Black (tiger)-This contains both a clot activator and gel. This is used for serum separation.
Red – This contains a clot activator. This is used when serum is needed. This is used to test for both blood donor screening as well as infectious disease.
Orange or Grey / Yellow (tiger)-This contains a clot activator, Thrombin. This is used for STAT serum testing (serum separation), the clot activator is rapid.
Order of the Draw
Along with the many types of blood collection tubes, the order in which the Phlebotomist uses these tubes is important. Known as the Order of the draw, one specific blood collection tube must follow another.
Because some collection tubes contain additives, accidentally mixing up the order could cause cross-contamination. This would occur when the additives of one tube would accidentally be added to another. Following the order of the draw ensures the collected blood can be used for testing. Along with the first three steps, the last draw must be completed in the order noted.
First – Yellow Blood culture tube or bottle
Second – Light Blue Coagulation tube
Third – Red Non-additive
Last– Red-Gray SST, contains clot activator
Green Sodium heparin
Lite Green PST, contains anticoagulant
Yellow ACDB or ACDA, contains acid citrate dextrose
Lite Gray Fluoride/Oxalate
It is important to note that non- additives such as the red collection tube is drawn before the collection tubes that contain additives such as the Green collection tube (containing Sodium heparin).
Each distinction, from the blood collection tubes and their colors to the order of the draw provides insight into the exacting standards of venipuncture that are in place to ensure the best possible blood collection for diagnostic testing.