Vascular access devices (VADs) are frequently used in healthcare to deliver medications and fluids, providing a reliable pathway into a patient’s bloodstream. These devices range from simple, short-term peripheral intravenous lines to more complex, long-term catheters. When a patient requires routine blood work, a common question arises regarding whether blood can be drawn from a midline catheter. While using the catheter already in place seems convenient, the answer depends on the device’s design, clinical policy, and associated risks. This article explores the technical possibilities and clinical recommendations for drawing blood from a midline catheter.
Defining the Midline Catheter
A midline catheter is a long, thin tube inserted into a peripheral vein, typically in the upper arm, to provide intravenous access for an extended period. These devices are generally longer than a standard peripheral IV, often ranging from 10 to 20 centimeters. The catheter is advanced until its tip rests in a large vein of the upper arm, such as the basilic, cephalic, or brachial vein, but it terminates below the axilla, or armpit.
This placement distinguishes a midline from a short peripheral IV and a PICC (Peripherally Inserted Central Catheter) line. Unlike a midline, a PICC line is advanced further until its tip reaches a central vein near the heart, such as the superior vena cava. The primary purpose of a midline is to deliver therapies well-tolerated by peripheral veins, such as long courses of antibiotics or intravenous hydration, for up to four weeks.
Feasibility and Policy for Blood Draws
It is technically possible to aspirate blood through a midline catheter; some manufacturers even design specific models for this purpose. The procedure involves attaching a syringe and applying negative pressure to withdraw the sample. Despite this technical feasibility, drawing blood from a midline is not the preferred or routine clinical practice in most healthcare settings.
Clinical guidelines often discourage routine blood collection because midlines are designed for infusion, not sampling. The catheter’s smaller internal diameter, compared to a central line, can make blood aspiration difficult, leading to sluggish flow or requiring excessive force. This can result in a failed draw or a compromised sample, which must then be discarded. Institutional policies vary; some facilities strictly prohibit the practice to preserve the catheter, while others allow it only as a last resort for patients with difficult venous access.
Recent research shows that blood samples taken from a midline, when performed using proper technique, can be clinically equivalent to a sample drawn from a peripheral stick. This suggests that for patients with very poor veins who require frequent testing, a midline draw may be an acceptable option under strict protocol. When permitted, the procedure requires meticulous attention, including discarding an initial waste volume (typically 5 to 10 milliliters) to prevent dilution by the catheter’s flushing solution.
Risks and Complications of Midline Phlebotomy
Attempting to draw blood from a midline introduces several risks that can compromise the patient’s health and the device’s function. One significant concern is the potential for catheter occlusion, or clotting. Repeated blood draws increase the manipulation of the catheter hub, raising the risk of introducing contaminants and leading to a catheter-related bloodstream infection.
Drawing blood involves pulling a sample against the natural direction of flow, creating negative pressure inside the catheter. This suction can cause the soft walls of the peripheral vein to collapse around the catheter tip, potentially damaging the inner lining of the vein. This mechanical irritation and trauma can contribute to the formation of a clot, specifically increasing the risk of superficial venous thrombosis.
A forceful blood draw can also result in hemolysis, where red blood cells are damaged and rupture. Hemolysis occurs when cells are pulled too rapidly through the catheter’s narrow lumen, making the sample unusable for laboratory analysis. Furthermore, if the initial waste volume is insufficient or not properly discarded, remaining saline or infused medications can dilute the sample, leading to inaccurate lab test results.
Alternative Methods for Necessary Blood Tests
Because of the potential for complications and the risk to the midline’s lifespan, healthcare providers prioritize alternative methods for obtaining blood samples. The preferred and most reliable method for routine lab work is a standard venipuncture, often called a peripheral stick, performed on a different vein. This approach maintains the integrity of the midline catheter for its primary use of delivering therapy, while providing a high-quality, undiluted blood sample.
If the patient has a central venous access device, such as a PICC line or a central line, that device is typically the next-best option for blood collection. These central lines are designed with wider lumens and terminate in larger, high-flow central veins, making them better suited for aspiration. Clear communication with the healthcare team is important to ensure the midline’s limitations are respected. Using the midline solely for infusions and opting for a separate peripheral stick for blood tests best preserves the longevity and function of the catheter throughout the patient’s treatment course.