The transfer of blood collected via a syringe into vacuum collection tubes is necessary when standard venipuncture methods are challenging or impossible. This technique is often employed for patients with fragile or small veins, or when precise control over aspiration pressure is required, such as in pediatric or geriatric cases. Successful execution requires meticulous technique to guarantee both the safety of the healthcare worker and the integrity of the collected blood specimen. This process requires specific equipment and procedural steps that safeguard the sample from pre-analytical errors like hemolysis or clotting, which can render the specimen unusable for testing.
Essential Safety and Equipment Preparation
Before the blood transfer begins, it is mandatory to prepare the workspace and don the appropriate personal protective equipment (PPE). The minimum PPE required includes fresh gloves and protective eyewear to guard against potential blood splatter. All necessary supplies must be staged, including the syringe, the correctly labeled collection tubes, and a designated sharps disposal container placed within arm’s reach.
The single most significant safety measure is the immediate and safe disposal of the needle used for the venipuncture. This needle must never be used to pierce the rubber stopper of a vacuum tube, as this poses an extreme risk of needlestick injury and can cause hemolysis. Once the draw is complete, the needle is immediately secured using its safety mechanism and discarded into the sharps container. Only a blunt blood transfer device, such as a Luer-lock access device, is permitted to puncture the tube stopper.
Understanding the Order of Draw
The sequence in which collection tubes are filled, known as the Order of Draw, is a standardized procedure that must be followed strictly, even when transferring blood from a syringe. This order is designed to prevent the carryover of chemical additives from one tube into the next, which could contaminate the specimen and lead to inaccurate test results. For instance, the EDTA anticoagulant from a lavender-top tube could falsely elevate potassium levels in a subsequent chemistry tube.
The standard sequence begins with blood culture bottles. The remaining tubes are filled in the following order:
- Light blue-top tubes (sodium citrate) used for coagulation studies.
- Serum tubes (red or gold-top) which contain clot activators or gel separators but no anticoagulant.
- Heparin tubes (green-top).
- EDTA tubes (lavender-top).
- Glycolytic inhibitor tubes (gray-top), which contain sodium fluoride and potassium oxalate.
Following this order ensures that the most sensitive tests are not compromised by interfering additives.
Step-by-Step Blood Transfer Technique
The physical transfer of blood must occur only after the venipuncture needle has been safely discarded and the blunt transfer device secured to the syringe tip. The transfer device, which often uses a Luer-lock mechanism, is securely twisted onto the syringe, ensuring an airtight connection. This device is engineered to safely pierce the rubber stopper of the collection tube.
The transfer begins by inserting the device into the stopper of the first collection tube in the correct Order of Draw. The vacuum pressure inside the tube will automatically draw the blood from the syringe. It is critical that the plunger of the syringe is not pushed down forcefully to expedite the process.
The vacuum should be allowed to draw the blood naturally until the tube is filled to its indicated volume. Forcefully pushing the plunger causes high-velocity flow, subjecting red blood cells to excessive shear stress, a leading cause of hemolysis. Once the tube is filled, it should be removed from the transfer device. If the tube contains an additive, it must be immediately and gently inverted the number of times specified by the manufacturer to ensure proper mixing.
Minimizing Risks to Sample Integrity
Maintaining the integrity of the blood specimen is paramount, as compromised samples lead to erroneous results and potential misdiagnosis. Hemolysis, the rupture of red blood cells, is a frequent pre-analytical error that must be actively prevented during the transfer. This damage releases intracellular components like potassium and hemoglobin into the plasma, which alters chemistry test results.
Rapid clotting, which can occur almost immediately upon blood collection, must also be prevented, especially for samples requiring whole blood or plasma. This is achieved by transferring the blood promptly and immediately mixing additive-containing tubes with gentle inversions once they are filled.
Correct fill volume is another critical factor, particularly for light blue-top coagulation tubes, where the ratio of blood to the sodium citrate additive must be precisely 9:1. Under-filling this tube results in an excess of anticoagulant, which can skew test results like the Prothrombin Time (PT). Over-filling or under-filling any tube with a liquid additive will compromise the concentration ratio and must be avoided. Proper post-transfer handling includes labeling tubes accurately and ensuring the specimen is transported to the laboratory under the correct temperature and handling conditions to preserve its quality.