Introduction

Using fresh blood samples for the complete blood count EQA program raises the challenge of guaranteeing stability. A study was set up to compare three different protocols for preserving fresh blood samples for haematology parameters. Two questions were of interest:  (1) which protocol is the best for preserving samples and (2) how many days can the samples be stored before analysis?

Material and methods

One blood donation from one single donor was used. The protocols were: (1) Adding a fixative (glutardialdehyde 0.025%) and storing at room temperature, (2) Adding a fixative and storing at 2-8°C, (3) Not adding any fixative and storing at 2 8°C. The samples were  analysed at day 0 in the afternoon , and at day 1, 2 and 3 in the morning and the afternoon, with day 0 as the day of preparation. The evaluated parameters were: white blood cell count (WBC), red blood cell count (RBC), haemoglobin (Hb), haematocrit  (Hct), mean corpuscular volume (MCV) and platelet count. The statistical analysis was performed by equivalence testing by means of confidence intervals around the mean changes based on the results of an Analysis of Variance after exclusion of outliers. For each protocol, comparisons with day 0 afternoon were made. The analyser used was ABX Micros ES60 (HORIBA Medical).

Results

For WBC, there is a lack of evidence that a sample stored at room temperature is still stable at day 1 in the afternoon. Samples stored at 2-8°C stay stable up to day 3 in the afternoon and the fixative does not seem to have a significant effect on the stability for the period considered in this study. For RBC, Hb and Hct, adding the fixative causes a change in the values that can be observed from day 0 on. While stability appears to be ensured for Hb through the three protocols, storage at room temperature makes RBC and Hct substantially to drop and stability is assured only for the first day. Storage at 2-8°C, in contrast, assures stability till day 3 afternoon. MCV appears to be very stable when the sample is kept at 2-8°C, but stability is not assured when the sample is kept at room temperature. Adding the fixative does not have an observable effect on MCV. Adding the fixative appears to have an effect on the measured platelet count, though. Storing the samples at room temperature provides stability until day 3; storing at 2-8°C assures stability until day 2.

Conclusion

For all parameters, stability is assured as long as the samples are stored at 2-8°C for two days. For all parameters except platelet count, this period can be extended up to three days. Except for platelet count, there is no evidence that adding a fixative prolongs stability. Adding a fixative however affects the assigned value of several parameters, which may cause a problem of commutability.