Although most modern analysers require only micro-volumes of plasma or serum to
perform a clinical chemistry test (e.g. 2 µl of sample is needed for glucose determination
on the Hitachi 747 autoanalyser), problems with blood collection may mean that
insufficient sample is obtained for the analysis of all the designated tests. Some
investigators suggest pooling samples for animals in the same group or cage and
analysing the pooled samples. This approach is not recommended since it can lead to
difficulties when interpreting the results. For example, pooling a grossly haemolysed
sample with four non-haemolysed samples will markedly increase the pooled potassium
value; however, there is no way of knowing how many samples were affected. When
samples of reduced volume are received, it is preferable that the tests should be
prioritized such that the important tests are analysed first for each individual. In extreme
circumstances a further blood collection for specific animals should be considered. If an
inadequate amount of blood is a regular occurrence, possibly because of large blood
volumes required