Venous, Arterial, and Capillary Blood Specimens

Venous blood is deoxygenated blood that flows from tiny capillary blood vessels within the tissues into progressively larger veins to the right side of the heart.

Venous blood is the specimen of choice for most routine laboratory tests. The blood is obtained by direct puncture to a vein, most often located in the antecubital area of the arm or the back (top) of the hand. At times, venous blood may be obtained using a vascular access device (VAD) such as a central venous pressure line or an IV start. Most laboratory reference ranges for blood analytes are based on venous blood.

Deoxygenated blood is pumped from the right side of the heart to the lungs, where it takes up oxygen. The now oxygenated blood is pumped through the left side of the heart via arteries.

The most common reason for the collection of arterial blood is the evaluation of arterial blood gases. Arterial blood may be obtained directly from the artery (most commonly, the radial artery) by personnel who are trained to perform this procedure and are knowledgeable about the complications that could occur as a result of this procedure. Arterial blood may also be obtained from a vascular access device (VAD) inserted in an artery, such as a femoral arterial line or catheter.

Capillary blood is obtained from capillary beds that consist of the smallest veins (venules) and arteries (arterioles) of the circulatory system. The venules and arterioles join together in capillary beds, forming a mixture of venous and arterial blood. The specimen from a dermal puncture will therefore be a mixture of arterial and venous blood along with interstitial and intracellular fluids.

Capillary blood is often the specimen of choice for infants, very young children, elderly patients with fragile veins, and severely burned patients. Point-of-care testing is often performed using a capillary blood specimen.