Ein Serum-Gel-Röhrchen is a collection tube designed for serum rather than plasma. It contains no Antikoagulans, because this sample is meant to clot. It carries a clot activator on the tube wall together with a gel whose density is between that of the blood cells and that of the serum. During centrifugation the gel moves and comes to rest between the two, forming a physical barrier that holds the serum away from the clot until the analysis.
The sequence matters more than the tube itself:
- The sample is drawn and inverted as the manufacturer states.
- It then stands upright and undisturbed until clotting is complete.
- Only then is it centrifuged, and only during that spin does the gel barrier form.
Before the spin there is no barrier at all, so a tube standing on a counter is still a sample in contact with its own cells and it keeps changing. That is why the tube type belongs to Präanalytik rather than to the analysis.
For a pharmacy without a centrifuge the division of work is simple, because the pharmacy performs the draw and the mixing while the laboratory performs the Serumgewinnung when the tube arrives. What the pharmacy controls in between is the standing position, the temperature and above all the time, because the interval the laboratory allows between collection and centrifugation is what makes the result usable.
Rough handling in that window, forceful mixing or a jolted transport box are also common routes to Hämolyse, which the gel cannot undo once it has happened.
The tube type is chosen by the laboratory rather than by the pharmacy or the customer. Some parameters are validated only for serum without gel, because the gel can bind certain substances or interfere with a later addition to the request, while others require plasma and a different tube entirely. The laboratory sets that out in its own handbook along with the filling order, the minimum volume and the maximum interval before centrifugation. A pharmacy asks for that document before the first appointment and works from it rather than from the tube colour.
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.
