Preparation and distribution of samples

Samples for blood count are usually prepared from microbiologically screened, discard venesection bags. Samples are partially fixed and aliquoted in-house.

The stabilisation or fixation of red blood cells alters their response to outside influences such as diluents, lysing agents and cytochemical dyes. The variation in response to these changes may be instrument-dependent, so the grouping of instruments for statistical analysis of performance is vitally important. Even the gentle fixation process used by CQAS still has influences on red cell shape, size, deformability and resistance to lysis. For all cellular components one also has to consider changes in optical and biochemical characteristics. These will impact both on basic enumeration of cells and differentiation of white cell types in particular.

Samples for plasma viscosity are prepared from screened NBS plasma and distributed in liquid form.

Samples D-dimer are prepared from screened patient plasma and distributed in liquid form.

Coagulation and haemoglobinopathy samples are all freeze-dried.

For coagulation samples this invariably involve freeze-drying of plasma and care is taken throughout the lyophilisation process to use appropriate buffers and stabilisers to prevent the deterioration of coagulation factors.

For haemoglobinopathy trials the sample should be such that sensitivity to varying, and clinically relevant, levels of abnormal haemoglobin subtypes is maintained. The aims of the trials should be to clearly separate and identify abnormal haemoglobins. In preparing the sample, the EQA provider must ensure that any small changes which take place during sample preparation do not impinge on the laboratories ability to be able to identify abnormality. (ie. the co-migration of abnormal haemoglobins in HPLC or electro-separation techniques as a result of pre-analytical manipulation).

  • All samples purchased from commercial sources are microbiologically screened.
  • All material is sent by Royal Mail – Airmail where required.