A Peripheral Intravenous (PIV) line is a short, flexible catheter inserted into a small vein, typically in the arm or hand, designed for short-term use in delivering fluids and medications. While traditional venipuncture remains the gold standard for blood collection, drawing from an existing PIV is a common practice. This method is highly conditional and often debated within healthcare settings. It is generally avoided unless a specific protocol is followed to mitigate the risks of sample inaccuracy and patient harm.
Why Drawing Blood From a PIV is Attempted
The primary motivation for drawing blood from an existing PIV is optimizing the patient experience and improving clinical workflow efficiency. Patients often require multiple blood tests daily, and repeated venipuncture causes increased pain, anxiety, and trauma. Utilizing an already-in-place PIV minimizes the number of painful needle sticks a patient endures during hospitalization.
This approach offers significant advantages in clinical efficiency, especially in fast-paced environments like the emergency department. Drawing from a PIV saves time for healthcare personnel and reduces the overall workload associated with performing separate venipunctures. Immediate access allows for rapid blood collection, which is useful when time-sensitive laboratory results are needed for urgent patient management.
For patients with poor or limited venous access, such as those with chronic illnesses, preserving veins is a major concern. Using an existing catheter helps protect remaining veins from the cumulative damage of repeated punctures. The convenience of access is a compelling argument for adopting PIV draws when appropriate protocols are strictly followed, but this must be balanced against the potential for compromising sample quality.
Maintaining Sample Quality
The largest technical challenge of drawing blood through a PIV is ensuring the integrity and reliability of the collected sample. A significant risk is the mechanical stress placed on red blood cells as they are pulled through the narrow catheter lumen, which can lead to hemolysis. Hemolysis is the rupture of red blood cells, which releases internal components, like potassium and lactate dehydrogenase, into the blood plasma. This can inaccurately elevate certain lab values, potentially leading to misdiagnosis or inappropriate treatment.
The small diameter of PIV catheters, especially those 20-gauge or smaller, increases the shear stress on the cells, making hemolysis a more frequent complication compared to traditional venipuncture. Samples can also be contaminated or diluted by residual fluids within the catheter, such as saline flushes or intravenous medications. Even a small amount of residual fluid can skew results for analytes like sodium or glucose.
To counteract dilution, a specific volume of blood must be discarded immediately before the sample is collected; this is known as the “waste” volume. This initial blood volume, typically 1 to 2 milliliters, clears the catheter and extension tubing of any contaminating fluids or flush solutions. The use of specialized vacuum tubes and avoiding excessive suction force can also help mitigate the risk of red blood cell damage.
Patient Safety and Procedural Limitations
Patient safety is the overriding concern when considering the use of a PIV for a blood draw, and strict contraindications limit when this procedure can be performed. The manipulation of the catheter hub during the draw introduces a risk of infection, potentially allowing bacteria to enter the bloodstream. Maintaining a meticulous sterile technique is therefore paramount to minimize the potential for a bloodstream infection.
Another procedural risk is the potential for damaging the vein or the catheter itself. Aggressive or forceful aspiration of blood can cause the vein to collapse around the catheter tip, leading to infiltration or phlebitis. This forceful suction can also dislodge the catheter, requiring a completely new PIV insertion and delaying patient care.
Specific clinical circumstances prohibit drawing blood from a PIV. A PIV actively infusing certain medications, such as vasopressors, chemotherapy agents, or blood products, should not be used for blood collection due to the risk of contaminating the sample with the drug. Additionally, catheters with a smaller gauge, such as 22-gauge or 24-gauge, are highly restrictive and inappropriate for drawing blood due to the increased risk of hemolysis. PIVs placed across areas of joint movement, like the wrist or antecubital space, are also avoided because of the risk of mechanical complication or positional occlusion during the draw. Finally, certain sensitive laboratory tests, particularly blood cultures or coagulation studies, may require a fresh venipuncture to ensure the highest degree of accuracy.