A finger stick, also known as capillary blood sampling, is a simple, minimally invasive technique used to collect a small volume of blood from the fingertip. This method draws blood from the capillaries beneath the skin, rather than from a larger vein. It is a common procedure for at-home monitoring and point-of-care testing because it requires only a few drops of blood. Finger sticks are frequently performed for self-monitoring of blood glucose levels, a regular practice for managing diabetes. This collection method is also employed for at-home testing kits designed to measure various biomarkers, such as cholesterol or coagulation factors like the International Normalized Ratio (INR).
Preparing Supplies and Selecting the Site
Before beginning the procedure, gather all necessary supplies and ensure the environment is clean. You will need a sterile, single-use lancet or lancing device, the specific collection medium (like a test strip or micro-collection tube), a fresh alcohol wipe, and sterile gauze. Wash your hands thoroughly with warm, soapy water and dry them completely to prevent contamination and reduce the risk of infection.
Selecting the puncture site carefully is important for both comfort and sample quality. The recommended site for an adult is the side of the middle or ring finger on the non-dominant hand. The sides of the fingertip have fewer nerve endings than the center pad and sufficient tissue depth to prevent bone injury. Avoid using the index finger or thumb, which are generally more sensitive, or fingers that are swollen or have visible calluses.
Step-by-Step Lancing and Collection
Once the site is chosen, use the alcohol wipe to clean the area and allow the skin to air-dry for several seconds. Air-drying is necessary because residual alcohol can cause stinging and may dilute or contaminate the blood sample, leading to inaccurate results. Prepare the lancing device by loading a new, sterile lancet and adjusting the depth setting, which typically ranges from 1.0 to 2.2 millimeters for adults based on skin thickness.
Press the lancing device firmly against the side of the fingertip, ensuring solid contact, and then trigger the stick. The firm pressure helps minimize pain and ensures the lancet reaches the capillary bed. Immediately wipe away the first drop of blood with a clean piece of gauze. This initial drop often contains interstitial fluid, which can dilute the sample and interfere with test accuracy.
To collect the sample, apply gentle pressure to the finger, starting from the base and moving toward the puncture site, allowing a second, rounded drop of pure capillary blood to form. Avoid aggressive squeezing directly at the puncture site, as this can cause hemolysis, or the rupture of red blood cells, compromising the sample integrity. Touch the collection medium—such as the test strip or micro-collection tube—to the blood drop, allowing it to draw the sample in by capillary action until the required amount is collected.
Post-Procedure Care and Safe Disposal
Immediately after collecting the required blood volume, place clean gauze or a cotton ball over the puncture site and apply gentle, steady pressure for about 30 seconds. This action helps to stop the bleeding quickly. Once the bleeding has stopped, apply a small adhesive bandage to protect the site from contamination.
Safe disposal of the used lancet is necessary to prevent accidental needle-stick injuries. Never attempt to recap or reuse a lancet, as this increases the risk of injury and infection. The used lancet must be immediately discarded into a designated sharps container, which is a specialized, puncture-resistant plastic container with a secure lid.
If an approved sharps container is unavailable, a heavy-duty, puncture-proof plastic bottle, such as a laundry detergent container, can serve as a temporary alternative. Once the sharps container is full, it must be disposed of according to local regulations. This may involve dropping it off at a hospital, pharmacy, or a designated hazardous waste facility.
Maximizing Blood Flow and Troubleshooting
If you are having trouble getting an adequate blood sample, several techniques can help increase blood flow to the fingers.
Techniques to Increase Blood Flow
Warming your hands beforehand is highly effective, as heat causes the blood vessels to dilate; this can be achieved by washing them in warm water or rubbing them together briskly. Allowing gravity to assist by holding your hand below your waist level before and during the collection can also encourage good blood flow to the fingertip. Gently massaging the finger from the palm toward the fingertip can further promote blood flow to the puncture site.
If the first attempt is unsuccessful, try using a different finger and adjusting the lancing depth setting slightly deeper on the device. Maintain the gentle pressure technique. Aggressively squeezing the finger can force tissue fluid out and dilute the sample, which may lead to inaccurate test results.