A hemacytometer is a counting chamber which can be used to count a variety of formed elements such as platelets.
(1) Dilute a well mixed anticoagulated whole blood sample 1:100 in diluent.
(2) Charge both sides of the hematocytometer with the diluted sample.
(3) Count the center large square on each side of the hemacytometer; this is composed of 25 smaller squares. According to convention, elements are counted if they lie on the topmost and leftmost lines, but not the bottommost or rightmost lines.
(4) Compare the counts of both squares. They should agree within 5% of each other. If not, repeat the count or the dilution step until they agree within 5%.
(5) Take the average of the two counts.
(number of elements in 1 cumm (1 microliter) =
= ((number of elements counted) * (dilution factor)) / ((number of squares counted) * (volume of squares counted))
platelet count in 1 microliter =
= ((number of platelets counted) * (100)) / (1 * 0.1) =
= (number of platelets counted) * 1000
• Use of hemocytometers has a high coefficient of variation (CV).
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Specialty: Hematology Oncology, Clinical Laboratory