Vacutainer tubes are specialized containers for blood sample collection. They use a pre-measured vacuum to draw a precise volume of blood from a patient’s vein for efficient, standardized collection. Their widespread use ensures sample integrity, crucial for accurate results and effective diagnosis.
Vacutainer Tube Components
Vacutainer tubes feature effective blood collection and preservation. Each tube is made of glass or plastic and sealed with a rubber stopper. The internal vacuum draws blood to a predetermined volume, preventing contamination and standardizing collection.
The stoppers are color-coded, with each color signifying specific additives. These chemicals prepare the blood sample for analysis. Anticoagulants prevent clotting for tests requiring whole blood or plasma, while clot activators promote rapid clotting for serum samples. Some tubes also contain gel separators, which form a stable barrier between cellular components and the fluid portion of the blood after centrifugation.
Matching Tubes to Diagnostic Tests
Tube top colors indicate contents and intended diagnostic use. Recommendations follow established clinical guidelines, like those from the Clinical and Laboratory Standards Institute (CLSI).
Red-top tubes often contain no additive or a clot activator. Without an additive, blood naturally clots, yielding serum after centrifugation. They are used for tests requiring serum (e.g., blood bank procedures, drug levels, serology) and can also serve as discard tubes.
Gold- or tiger-top tubes (Serum Separator Tubes or SSTs) include a clot activator and a gel separator. The clot activator promotes faster clotting; the gel creates a barrier between serum and clotted blood cells after centrifugation. These tubes are used for chemistry determinations, including Comprehensive Metabolic Panels (CMP), Lipid Panels, and thyroid function tests.
Light blue-top tubes contain sodium citrate as an anticoagulant. This prevents clotting by binding to calcium ions, yielding plasma. They are designed for coagulation studies, such as Prothrombin Time (PT/INR), Activated Partial Thromboplastin Time (aPTT), and D-dimer tests. A precise blood-to-additive ratio is important for accurate results.
Lavender- or purple-top tubes contain Ethylenediaminetetraacetic acid (EDTA) as an anticoagulant. EDTA prevents clotting by chelating calcium ions, making them suitable for whole blood or plasma collection. They are used for hematology tests, including Complete Blood Count (CBC), hemoglobin A1c (A1C), and erythrocyte sedimentation rate (ESR). EDTA also helps preserve cellular components for blood typing and DNA analysis.
Green-top tubes contain heparin, an anticoagulant. Heparin enhances antithrombin III activity, inhibiting clotting factors and yielding a plasma sample. These tubes are used for various plasma chemistry tests, such as Basic Metabolic Panels (BMP) and ammonia levels.
Gray-top tubes contain sodium fluoride and potassium oxalate. Sodium fluoride acts as an antiglycolytic agent, preserving glucose levels by inhibiting breakdown, while potassium oxalate functions as an anticoagulant. These tubes are used for glucose and lactate measurements, and sometimes for blood alcohol levels.
Yellow-top tubes, often containing Acid Citrate Dextrose (ACD), serve as an anticoagulant and cell preservative. ACD maintains blood cell viability, making them suitable for specialized tests. Applications include DNA studies, paternity testing, and tissue typing for transplant compatibility.
Sequential Blood Collection
When multiple blood samples are required from a single venipuncture, a specific “order of draw” prevents additive cross-contamination. This sequence follows standards from organizations like the Clinical and Laboratory Standards Institute (CLSI). Adhering to this order maintains sample integrity and ensures accurate laboratory results.
The generally accepted order of draw for evacuated tube systems is:
- Blood culture bottles.
- Light blue-top tubes (sodium citrate).
- Serum tubes (red, gold, or tiger-top), which may or may not contain clot activators or gel.
- Heparin tubes (green tops).
- EDTA tubes (lavender/purple tops).
- Glycolytic inhibitor tubes (gray tops).
This careful sequencing minimizes the risk of additive carryover, which could otherwise interfere with subsequent test results.