Quality control in blood cell analysis

Abstract

In the literature various methods are described for quality control in the determination of haemometric and haemocytometric values. In most clinical laboratories, commercial blood cell control material is utilised in internal quality control. Although it is claimed that the materials do not change markedly within 4 to 6 weeks, variations may occur. The values assigned to the materials are determined by utilising various blood cell analysers in selected laboratories, and may vary according to the type of instrument. Since the analytical results should be the same for every type of instrument, one may deduce that, by using such materials, only the repeatability and reproducibility, i.e., the constancy of performance of the instrument is checked. Although the use of the materials has some advantages, it is clear that accuracy is not guaranteed where there is lack of a calibrator.

In the National Institute of Public Health and Environmental Hygiene (RIVM) in the Netherlands, efforts were made to improve on the methods of quality control in haematology. After studying five methods mentioned in the literature for the preparation of stabilised erythrocytes, the method described by Benedek (1966) was found to be the best when taking into consideration the shapes of the cells, the suitability for counting, and the stability. In a contract with the Council of Europe the method was further developed.

Thorough studies were also undertaken into the performance of cell counting instruments. In collaboration with nine clinical laboratories we succeeded, taking into account the basic anomalies of the various types of blood cell counting instruments, in determining the concentration of a suspension of stabilised cells (Stabicells) to a tolerance of less than 2%. As its lifetime is virtually unlimited, this suspension may be considered to be a calibrator.

A comparable procedure was used to prepare a calibrator for the automated determination of haemoglobin concentration. The concentration could be shown not to deviate markedly within a period of 3 years.

Using a combination of technical anomaly corrections with quality control by daily calibration, we set up a system independent of external control. Since in animal haematology, problems are greater than in human haematology, and external support is less available, application of the system is strongly recommended in animal haematology.