Venous aspiration is useful because it is a noninvasive way of obtaining cells and extracellular fluid (plasma) from the body for analysis. And since the blood flows through the whole body - thus serving as the medium responsible for providing oxygen and nutrients to the body and pushing waste products to the excretory system for disposal, the degree of blood flow is affected by many diseases, and even affects them. For all these reasons, blood tests are among the most frequently performed medical examinations for patients.

The phlebotomy technician, laboratory technician, and nurse are responsible for drawing the blood sample from the patient. However, in emergency situations and in special cases, the paramedic and the doctor draw blood. In addition, the respiratory therapist is trained to draw arterial blood for arterial blood gas analysis.