A capillary blood sample allows for the collection of a small volume of blood from the tiny vessels near the skin’s surface. This technique is commonly used for at-home diagnostic testing, such as monitoring blood glucose levels for diabetes management or collecting samples for mail-in laboratory tests. Collecting a proper sample requires careful preparation and technique to ensure the blood is clean and the volume is sufficient. Understanding the correct steps helps to minimize discomfort and prevent the need for a repeat puncture.
Gathering Supplies and Choosing the Best Site
Before beginning the process, gather all necessary materials. You will need a sterile, single-use lancet, the specific collection item (such as a test strip or micro-collection tube), an alcohol wipe, a clean cotton ball or gauze, and a puncture-proof sharps container. Proper preparation includes increasing blood flow, which is achieved by washing your hands with warm water and soap or by gently rubbing the chosen finger.
The most suitable location for a finger prick is the ring or middle finger on your non-dominant hand. These fingers generally have enough tissue to provide a good sample while avoiding the more sensitive nerves and calluses often found on the index finger. Puncturing the side of the fingertip, rather than the fleshy pad or the very center, is recommended because the sides have fewer nerve endings and better capillary flow. Avoid using the pinky finger, as it has less soft tissue protecting the underlying bone structure.
Executing the Finger Prick Technique
After selecting the site, use an alcohol wipe to clean the area thoroughly, then allow the alcohol to air dry completely. If the alcohol is not fully dry, it can cause a stinging sensation upon puncture and contaminate the blood sample, leading to inaccurate results. Next, prepare the lancing device by setting the appropriate depth based on your skin thickness, noting that a deeper setting yields more blood but can cause more discomfort.
Press the lancing device or safety lancet firmly against the chosen side of your fingertip to ensure a stable, secure puncture. Maintaining firm pressure helps to compress the tissue, which aids in blood flow and makes the puncture more effective. Activate the lancet mechanism, and then immediately set the device aside. The goal is a quick, continuous action to create a clean puncture that promotes good blood flow.
Collecting the Sample and Safe Disposal
Once the puncture is made, the first drop of blood should be wiped away gently using a clean piece of gauze or cotton. This initial drop often contains tissue fluid, residual alcohol, or skin debris that could dilute the sample or interfere with test results. After wiping the first drop, a second, clean drop will typically form.
Encourage the formation of this second drop by gently massaging the finger from its base toward the puncture site, avoiding forceful squeezing directly at the fingertip. Excessive pressure or vigorous milking risks sample dilution by mixing tissue fluid with the blood. Allow the blood drop to fall naturally onto the collection strip or into the tube without touching the skin to the collection surface. After collecting the sample, apply light pressure to the puncture site with a clean cotton ball or gauze until the bleeding stops.
The used lancet must be disposed of safely to prevent injury or infection. Immediately place the entire used lancet, without attempting to recap or dismantle it, into a designated sharps container. This container should be made of hard, puncture-proof plastic, such as a specialty sharps box or a heavy-duty laundry detergent bottle with a secure, screw-on lid. When the container is about three-quarters full, it should be sealed and disposed of according to local guidelines, which often involves drop-off locations at pharmacies or hospitals.