The hemocytometer or haemocytometer is a device originally designed for the counting of blood cells. It is now also used to count other types of cells as well as other microscopic particles.
Automated cell counters sample the blood, and quantify, classify, and describe cell populations using both electrical and optical techniques. Electrical analysis involves passing a dilute solution of the blood through an aperture across which an electrical current is flowing. The passage of cells through the current changes the impedance between the terminals (the Coulter principle). A lytic reagent is added to the blood solution to selectively lyse the red cells (RBCs), leaving only white cells (WBCs), and platelets intact. Then the solution is passed through a second detector. This allows the counts of RBCs, WBCs, and platelets to be obtained. The platelet count is easily separated from the WBC count by the smaller impedance spikes they produce in the detector due to their lower cell volumes.
Optical detection may be utilised to gain a differential count of the populations of white cell types. A dilute suspension of cells is passed through a flow cell, which passes cells one at a time through a capillary tube past alaser beam. The reflectance, transmission and scattering of light from each cell is analysed by sophisticated software giving a numerical representation of the likely overall distribution of cell populations.
Reticulocyte counts can now be performed by many analysers, giving an alternative to time-consuming manual counts. Many automated reticulocyte counts, like their manual counterparts, employ the use of a supravital dye such as new methylene blue to stain the red cells containing reticulin prior to counting. Some analysers have a modular slide maker which is able to both produce a blood film of consistent quality and stain the film, which is then reviewed by a medical laboratory professional.
Examples of full blood count machines are:
- Abbott Cell-Dyn product line
- Sysmex XE-2100
- LH 700 series
- Medonic M Series
Coagulometers
Automated coagulation machines or Coagulometers measure the ability of blood to clot by performing any of several types of tests including Partial thromboplastin times, Prothrombin times (and the calculated INRs commonly used for therapeutic evaluation),Lupus anticoagulant screens, D dimerassays, and factor assays.
Coagulometers require blood samples that have been drawn in tubes containing sodium citrate as an anticoagulant. These are used because the mechanism behind the anticoagulant effect of sodium citrate is reversible. Depending on the test, different substances can be added to the blood plasma to trigger a clotting reaction. The progress of clotting may be monitored optically by measuring the absorbance of a particular wavelength of light by the sample and how it changes over time.
Coagulation machines include:
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