Performing A Manual Differential And Assessing Red Blood Cell Morphology

Principle

When blood samples are evaluated by the use of automated hematology analyzers, this analysis includes automated differentials. Specific criteria pertaining to normal, abnormal, and critical values have been programmed into the analyzers by the institution, and if the differentials do not meet these criteria, verification is necessary. This is done by performing manual differentials and further evaluating the peripheral smear. First, a differential white blood cell (WBC) count is performed to determine the relative number of each type of white cell present. Technologists/technicians must recognize and properly record the type(s) of white cell observed. Simultaneously, red cell, white cell, and platelet morphology is noted and recorded. Also, a rough estimate of platelets and WBC counts is made to determine if these numbers generally correlate with the automated hematology analyzer. Technologists/technicians must be proficient at recognizing red and white cell abnormalities, identifying them correctly, and quantifying them.

Reagents and Equipment

1. Microscope

2. Immersion oil

3. Differential cell counter

Specimen Collection and Storage

Well-made stained blood smear obtained from a capillary puncture or an EDTA tube at least three-fourths full.

Quality Control

The slide should have three zones: head, body, and tail (Fig. 20.7). In the tail area, neutrophils and monocytes predominate, while red cells lie singly. In the body area, lymphocytes predominate, and red cells overlap each other to some extent.

306 PartV • Laboratory Procedures

Head

Body

Tail (includes feathered edge)

Head

Body

Tail (includes feathered edge)

306 PartV • Laboratory Procedures

Blood Smear Slide Feathered Edge

Figure 20.7 Three zones of wedge preparation.

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