Selecting a proper site is an important step in avoiding pre-analytical errors during the capillary collection process. The site should be free of calluses, scars, burns, blisters, rashes, cuts, scrapes, and bruises. The site should not be cyanotic, swollen, or infected. If the finger or the heel is cyanotic, applying a warming device such as a heel warmer for 3 to 5 minutes will increase the blood flow to the site. The warming device temperature should not exceed 42°C, as it may burn the patient.
Blood should not be collected from the fingers of a hand on the same side as a mastectomy. The removal of the lymph nodes may result in increased lymph fluid on the site of surgery. If a double mastectomy was performed, it is recommended to consult with the ordering physician on whether or not to perform the puncture. Blood should not be collected from the side or very tip of the middle or ring finger, as the distance between the surface and bone is much less; bone injury is more likely. The thumb has its own pulse and should be avoided. The pinky finger should also be avoided because it has the least amount of tissue between the surface and the bone of all the fingers; bone injury is possible when using this finger.
For a finger puncture, the middle or ring (3rd or 4th) fingers of a non-dominant hand are the best sites for collection. The puncture site should be in the central, fleshy portion of the finger, slightly to the side of the center and perpendicularly to the grooves or whorls of the fingerprint to prevent blood from running into those groves and down the finger. A heel puncture should be performed on the medial or lateral plantar surfaces of the heel or the great toe. The image to the right indicates the correct areas for heel puncture.