During storage many analytes will change, some in a way that can have a clinical implication, for example glucose and platelet numbers.

The glucose value cannot be used as the blood has been left in room temperature too long without centrifugation and separation of the blood cells from serum. Glycolysis will continue in the blood cells consuming glucose. Glucose in the sample will therefore be reduced. Under normal conditions glucose will decrease with 5-10% per hour, even more if leucocytosis is present.

Glucose should be analysed as soon as possible after sampling, or the tube must be centrifuged, and serum separated from the blood cells. Special collecting tubes containing NaF can be used to block glycolysis (grey top). F complexes with Mg, a cofactor needed for glycolysis to occur.

Platelets are very reactive and when blood is collected they are activated by contact with the tube walls. They have then plenty of time during storage to form aggregates. Aggregates are too large to be counted in the haematology instrument and the platelets in the aggregates are not counted properly, yielding a lower platelet number. This can easily be checked for by doing a smear and looking for the aggregates. The more and the larger the aggregates, the higher the impact is on the platelet counting. Aggregates are often most numerous in the feathered edge.