A capillary sample is a blood sample collected by pricking the skin. Capillaries are tiny blood vessels near the surface of the skin.

Blood transports oxygen, food, waste products, and other materials within the body. It also helps regulate body temperature. Blood is made up of a fluid called plasma and cells. Plasma contains various dissolved substances. The cellular portion consists primarily of red blood cells, but also includes white blood cells and platelets.

Because blood has multiple functions, tests on the blood or its components can provide valuable clues in the diagnosis of a multitude of medical conditions.

Capillary blood sampling offers several advantages:

• It is relatively easy to obtain (it can be difficult to obtain blood from the veins, especially in infants).
• There are several collection sites on the body (heel, fingertips, etc.) and these can be rotated.
• Testing can be performed at home and with minimal training. For example, diabetics must check their blood sugar several times a day using capillary blood sampling.

There are some disadvantages to capillary blood sampling.

• Only a limited amount of blood can be obtained using this method.
• There are some risks associated with the procedure (see below).
• Capillary blood sampling may provide inaccurate results, such as falsely elevated sugar, electrolyte, and blood count values.

Some blood tests are performed on blood obtained by pricking the skin of the finger, heel, or other areas and collecting a drop (or a few drops) of blood on a test strip or into a small container.

The area is cleansed with antiseptic and pricked with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

Some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.