A capillary puncture looks like the simplest part of a blood draw and is the part where technique decides most. The Punktionsstelle is the side of the finger pad, roughly where the pad curves round towards the nail edge, and not the centre of the pad and not the very tip. The centre and the tip carry the densest nerve endings, so a puncture there hurts more than it has to, and on a hand that works the skin is often thicker there as well. The middle or ring finger of the less used hand is the usual choice. The thumb and the index finger are avoided, and the little finger has too little tissue over the bone.
Blood flow at the fingertip decides the rest. A cold hand gives nothing, so the hand is warmed first, by letting it hang down for a moment, by rubbing it, or with a warm cloth where one is available. The disinfectant is applied and then allowed to dry completely, because a wet surface stings on puncture and dilutes the drop that follows. The puncture itself is made in a single movement with an Einmalstechhilfe held flat against the skin, and the device goes straight into the disposal container afterwards.
The first drop is wiped away with a dry swab. It is mixed with tissue fluid and with whatever remains of the disinfectant, and it is the drop least representative of the blood the laboratory wants to measure. Everything after it is collected, letting the drops form on their own and touching the collection vessel to the drop rather than to the skin.
The error worth remembering is squeezing. Milking the finger to force a drop out presses interstitial fluid into the sample and damages red cells on the way, which is how a capillary sample arrives showing Hämolyse and a potassium value that means nothing. Diluted, haemolytic capillary blood is the classic reason a kapillare Blutentnahme has to be repeated, and the repeat is considerably more unpleasant than getting the first attempt right. If the blood does not come, the answer is a warmer hand, the hand held lower, and a fresh puncture at a different site, never more pressure on the finger.
All of this sits in Präanalytik, before any analysis begins, and it is written down rather than left to habit, so that every person doing the draw chooses the same site and follows the same sequence. Hygiene bei der Blutentnahme covers the parallel requirements around the same few minutes, from gloves and skin disinfection through to disposal of the used lancet.
This glossary entry is general information about German pharmacy law and practice. It is not legal advice. For binding guidance on your own pharmacy, contact your Landesapothekerkammer.
