Automated Cell Counter

What is the Coulter principle for particle counting?

Coulter principle, also known as electrical impedance principle, is that biological cells are poor electrical conductors, as compared with a saline solution. If the fluid in a beaker is an electrolyte, an electrical current can be established between electrodes inside the tube and outside the tube. When the fluid (electrolyte) containing cells or particles is drawn through the orifice in the tube, the cells, being poor conductors of an electrical current, momentarily cause a decrease in the voltage. Each time a cell or particle passes into the path of the current, a voltage drop occurs. The magnitude, or size, of the voltage drop is proportional to the volumetric size of each cell. The voltage drops are fed into a complex electric circuit, which can discriminate between different amounts of voltage drops. The electric circuit then generates counting pulses for those cells larger than a certain size, or above a certain threshold level, thus counting the cells.

A technologist performs an automated blood count the RBC = 3.06 106 / L, hemoglobin = 12.2 g/dL and the hematocrit = 36.8%. Do these results conform to the rule of three? Should the technologist report these results? If not, what should he or she do next?

No, the technologist should not report the results because they do not conform to the "rule of three" (the RBC is too low). The tech should check the patient's blood smear for red cell agglutination or rouleaux, which would falsely decrease. He or she should also check for a lipemic specimen, failure to add lysing reagent, failure to mix lysing reagent and dilution errors. These errors would falsely increase the hemoglobin result.

A person has an RDW of 15.9 fL, what morphologic characteristic would be seen on his blood smear?

anisocytosis

define coincidence as it applies to cell counting

coincidence refers to two (or more) cells passing through the aperture at the same time. instead of counting them as two cells, the instrument would count them as one large cell

a solution capable of conducting an electrical current is called what?

electrolyte

would you expect a person with iron deficiency anemia to an increased or decreased RDW?

increased

what is a histogram?

it is a graphic representation of a population. in hematology, we use histograms to represent cell populations

newer cell counting instruments use _________ technology to eliminate the effect of coincidence

laminar flow

rouleaux are caused by excessive _______ and lipemia is caused by __________

protein, triglycerides (fat)

The "rule of three" for the complete blood count refers to the fact that the ____________ x 3 ≈ the hemoglobin and the ____________ x 3 ≈ the hematocrit.

red cell count, hemoglobin

correct CBC results can be obtained when rouleaux or lipemia are present by what?

saline replacement

what does the RDW measure?

the RDW is a measure of variation of cell size. it is a calculation of the coefficient of variation of the red cell volume

what is the purpose of having the external and internal electrodes attached to the aperture tube?

they establish an electrical current through which the cells pass and are counted

Patient's blood is run through the automated cell counter. The print-out shows a minus sign in front of the RBC, HGB and HCT. What does the minus sign tell the operator?

those results are below the established reference range

correct CBC results can be obtained when cold reacting antibodies (agglutinins) are present by what?

warming the specimen to 37°C and repeat the count