Optimization of Formaldehyde Fixative Concentration for Individual Blood Cells to Develop a Stabilized Blood Control for Automated Hematology Analyzers.

In a modern haematology laboratory, the complete and differential counts of blood are performed using complex haematology auto analyzers. In order to ensure the accuracy and reliability of test results, various regulatory authorities have prescribed the use of stabilized blood controls. The major pitfalls of these blood controls are their short shelf life. This could be due to the fact that they are prepared by a common cocktail of fixatives which acts on the discrete cells in various ways and would result in either under-fixation or over-fixation of various cells. Thus, in the present study, we have explored and optimized fixative and buffering for individual cells to achieve stable blood control. Blood cells were isolated using the centrifugation technique and were fixed individually with different concentrations of formaldehyde. After fixation, cells were pooled. Analysis of cell count was done till six months. Cells were also analysed morphologically to see the effect of fixation and storage on cell morphology. In the present study we compared the effect of the concentration of formaldehyde fixative for individual cells in the blood and their role in enhancing the shelf life and maintaining the morphology of the cells when suspended in plasma or suitable buffers post-fixation. It was observed that WBCs can be better fixed with 3 and 3.5% formaldehyde in a buffered solution, whereas RBCs and Platelets can be optimally fixed with 2.5% formaldehyde in a buffered solution.