Drawing blood from an existing intravenous (IV) line is a common hospital practice that prioritizes patient comfort and preserves access sites, avoiding repeated needle sticks. This method is convenient, especially when frequent sampling is required. The primary goal is to obtain a blood sample truly representative of the patient’s circulating blood, preventing contamination from the IV infusate while maintaining the integrity of the IV access device.
Assessing Line Suitability for Blood Sampling
Before attempting a blood draw, confirm the IV line is appropriate for sampling to ensure patient safety and accurate lab results. Central venous catheters (CVCs) and peripherally inserted central catheters (PICCs) are typically designed for both infusion and blood collection. Peripheral IV lines are smaller and may not be supported for blood draws by all facility policies due to the risk of hemolysis (destruction of red blood cells).
Lines actively infusing substances like total parenteral nutrition (TPN), lipids, or chemotherapy agents are unsuitable as they severely contaminate the sample. If the line is appropriate, any continuous infusion must be paused for at least two minutes before the draw. This allows the infused fluid to clear from the catheter tip, preventing sample dilution and artificially lowering blood component values like hemoglobin or electrolytes.
Essential Equipment and Sterile Preparation
Gathering all necessary supplies beforehand helps maintain a sterile field and ensures an efficient procedure. Required items include protective personal equipment (PPE) such as gloves and eye protection, and a skin antiseptic for cleaning the IV access hub.
Specialized equipment is needed for the collection process:
- A 10 mL syringe containing normal saline for flushing the line.
- A designated waste syringe (3 mL to 10 mL).
- Appropriate blood collection tubes, organized by the correct order of draw.
- A needless connector or blood transfer device to safely fill the vacuum tubes.
- Proper labeling materials for immediate sample identification.
Step-by-Step Blood Collection Technique
The collection process begins with meticulous hand hygiene, application of gloves, and confirming patient identity against the lab request. If an infusion is running, stop it, and vigorously scrub the IV line hub with an approved antiseptic wipe for the recommended time to prevent microbial contamination. Attach the first syringe, known as the waste syringe, to the cleaned access port.
The waste blood is drawn to clear the catheter of any residual IV fluid or saline that would otherwise dilute the sample. Standard practice often dictates withdrawing 3 mL to 5 mL of blood to ensure all infusate is removed from the catheter’s dead space. This discarded volume is important because drawing a sample contaminated with IV fluids can lead to significantly misleading test results.
After the waste is collected and safely discarded, attach the next syringe to withdraw the actual blood samples required for testing. Gently pull back the plunger to avoid excessive negative pressure, which could collapse the vein or cause hemolysis. The blood is then transferred from the syringe into the vacuum tubes using the blood transfer device in the specified order of draw.
Order of Draw
- Blood culture bottles (to prevent contamination).
- Coagulation tubes (light blue top).
- Serum tubes (red or gold top).
- Tubes with additives like EDTA (lavender top) or glucose inhibitors (gray top).
Finalizing the Procedure and Documentation
Once all required samples are collected, the access device used for the blood draw is removed, and the IV line is flushed to maintain patency. This is typically done by slowly injecting 10 mL of normal saline using a pulsatile or “push-pause” technique. This method creates turbulence to better clear the catheter lumen, helping prevent blood clots and fibrin buildup inside the catheter, preserving the line for future use.
After flushing, any continuous infusions that were paused should be restarted at the prescribed rate. Inspect the IV insertion site for any signs of complications, such as swelling, pain, or redness, which could indicate phlebitis or infiltration. The collected blood samples must be labeled immediately at the bedside, including the patient’s identifying information, time of collection, and the initials of the person who performed the draw. Document the procedure in the medical record, noting the time of the draw, the amount of blood discarded for waste, and the patient’s response to the procedure.