Drawing blood from an intravenous (IV) line provides a method for obtaining a blood sample without the need for a separate needle stick, which is beneficial for patients requiring frequent testing. This technique involves accessing the vascular access device to withdraw blood, rather than performing traditional venipuncture into a peripheral vein. The goal of this procedure is to secure an accurate blood sample for laboratory analysis while maintaining the sterility and function of the IV line. Because this process is specialized and involves vascular access, it must only be performed by trained healthcare professionals who adhere to established institutional protocols.
Essential Pre-Procedure Requirements
Before accessing any IV line for a blood draw, the healthcare professional must confirm the patient’s identity using at least two identifiers and verify the laboratory orders. The IV line must be assessed for suitability, noting if it is a peripheral IV or a central venous access device (CVAD), and confirming it is functional without signs of complication such as infiltration or infection.
A critical step is gathering all necessary supplies:
- A sterile collection kit
- Syringes of appropriate size (often 10 mL or larger for central lines)
- A blood transfer device
- Vacuum tubes
- Antiseptic wipes
- Saline flushes
- Personal protective equipment like gloves
Infection control is paramount, beginning with thorough hand hygiene and the donning of new, clean gloves. The access port—often a needleless connector—must be prepared following a strict disinfection protocol, commonly referred to as “scrub the hub.” This involves vigorously cleaning the connection port with an antiseptic agent, such as 70% alcohol or chlorhexidine, for 15 to 30 seconds. Allowing it to air dry completely ensures microbial kill and minimizes the risk of introducing bacteria into the bloodstream.
Step-by-Step Blood Collection Technique
Once the access port is disinfected, temporarily halt any running intravenous infusions, ideally for at least two minutes, to prevent dilution or contamination of the blood sample. The line’s patency is then confirmed by attaching a pre-filled saline syringe and gently aspirating to check for a smooth blood return. After confirming patency, the line is flushed with a small volume of saline to clear any medication or solution present in the catheter’s lumen.
The subsequent step involves drawing the “waste” or “discard” volume of blood. This volume is necessary to completely clear the IV line of the saline flush and any residual IV fluids or anticoagulant lock solutions, such as heparin, which could alter the lab results. The amount collected is determined by institutional policy, but it often ranges from 3 to 5 milliliters for most peripheral and central lines. This waste syringe is then detached and immediately discarded according to biohazard protocols.
Following the waste draw, attach a new, clean syringe and slowly withdraw the actual blood sample. Maintain a slow, steady aspiration pressure to prevent the collapse of the vein and to avoid hemolysis, which is the rupture of red blood cells that can skew test results. Once the required volume is collected, the syringe is removed, and the blood is transferred into the appropriate vacuum collection tubes using a specialized blood transfer device. Tubes must be filled in the correct order of draw—a standardized sequence that prevents chemical additives from contaminating the sample—and gently inverted the required number of times to mix the blood with the tube’s additive.
Maintaining Line Patency and Patient Safety
After the sample is collected and transferred, the focus shifts to restoring the IV line’s function and ensuring patient safety. The catheter lumen must be thoroughly flushed again, typically with a 10-milliliter syringe of 0.9% sodium chloride (normal saline), using a push-pause technique. This vigorous flushing action clears any remaining blood from the catheter wall, preventing clotting and maintaining the line’s patency. For certain central lines, a final “lock” solution, such as an anticoagulant like heparin, may be instilled following the saline flush to keep the line open between uses, depending on institutional policy.
The access port is then disconnected and secured with a new, sterile cap to maintain the closed system and prevent contamination. Throughout and immediately after the procedure, the provider must assess the patient for any signs of adverse reaction, such as pain, swelling, or bleeding at the insertion site. Finally, all procedural details must be accurately documented in the patient’s medical record, including the time of the draw, the volume of waste blood withdrawn, and the post-procedure condition of the IV line.