Reihenfolge der Blutentnahme is the order in which the individual tubes are filled during a single venöse Blutentnahme. It looks like a ritual, but it is not one, because every tube contains an additive and a trace of that additive can reach the next tube on the Kanüle or through the holder. The order is the control for that contamination, which is why it belongs to Präanalytik rather than to personal preference.
The consequence is easier to remember than any sequence, because an Antikoagulans does its work by chemistry, so a few microlitres arriving in the wrong tube change the chemistry of that sample too. Contamination changes different values depending on the additive involved.
- A tube whose additive binds calcium will disturb any analysis that depends on calcium if it reaches the next tube.
- A salt of an anticoagulant brings its own cation with it, so a potassium result from a contaminated tube can look raised without anything being wrong with the person.
- Clotting parameters are the most sensitive of all, because a citrate tube depends on a fixed ratio between citrate and blood and is only valid when it is filled to its mark.
None of this is visible as an obvious defect, because the sample looks normal and the result looks plausible, so only the constellation of values gives it away.
Dead volume causes the same kind of error at the start of a draw. When a Butterfly-Kanüle is used, the tubing between the wing and the holder is filled with air at the start of the draw. That air goes into the first tube, so the first tube is underfilled by exactly the volume of the tubing. If the first tube is the one with a required fill mark, the ratio is wrong before the sample has left the room. The standard answer is to draw a discard tube first, purely to prime the line, and to fill the tube that depends on its mark only once blood is already in the tubing.
Which order applies is not for the pharmacy to decide. Tube systems differ between manufacturers and laboratories issue their own instruction, so the binding sequence is the one the receiving laboratory publishes for the tubes it supplies. That sheet goes on the wall at the draw station and into the written procedure, and it is checked again whenever the laboratory or the tube system changes.
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.
