White blood cell count

differential white cell count

 A differential white cell count provides information on the different white cells present in the circulating

blood, i.e. neutrophils, lymphocytes, monocytes, eosinophils, basophils (rarely seen). Providing the

total WBC count is known, the absolute number of each white cell type, i.e. number of each cell per

litre of blood, can be calculated and an assessment made of whether the number of a particular cell type

is increased or decreased (compared with the accepted reference range).

Method

As previously discussed, it is only possible to report blood films reliably providing the thin blood film is

well made and correctly stained. Allow the stained film to dry completely before examining it.

1 Place a drop of immersion oil on the lower third of the blood film and cover with a clean cover

glass.

2 Examine the film microscopically. Focus the cells using the 10x objective with the condenser iris

closed sufficiently to see the cells clearly. Check the staining and distribution of cells.

3 Move to a part of the film where the red cells are just beginning to overlap and bring the 40x

objective into place. Open the iris *

*These values are guideline figures only. They should be checked locally. Neutrophil counts are lower in Africans

and Afro-Caribbean people.diaphragm.

4 Systematically examine the blood film and count the different white cells seen in each field, preferably

using an automatic differential cell counter

Differential WBC cell counter

Electronic and mechanical differential cell counters are available.  It is recommended because it is robust, easy to use and does not require batteries or mains electricity to operate it. When a total of 100 cells have been counted,

there is an audible signal. The numbers of each cell type are read from the display windows. Turning the knob on

the side returns all the displays to zero.

5 Calculate the absolute number of each white cell type by multiplying the number of each cell

counted (expressed as a decimal fraction) by the total WBC count.

Example

If: Percentage of neutrophils counted = 80%

i.e. 0.80 when expressed as a decimal fraction.

If total WBC count=8.6 x 109/l

Absolute neutrophil count is 0.80 x 8.6 =

6.9 x 109/l

Reporting absolute numbers of each cell type

When only the percentage of each cell type is reported in a differential WBC count and not the number per litre of

blood (absolute count), this can be misleading, e.g. in the above example, a neutrophil percentage count of 80% is

‘abnormal’ but when expressed in absolute numbers the neutrophil count is 6.9 x 109/l which is within the

normal reference range for an adult (see reference range figures).

6 Report the presence of white cell abnormalities, including:

– Left shift of neutrophils and toxic granulation

– Hypersegmented neutrophils

– Reactive (atypical) lymphocytes

– Malaria pigment in white cells

7 Report the appearance of the red cells, including:

– Variations in red cell staining, e.g. hypochromic cells, polychromatic cells, dimorphic

blood picture. If normal, refer to the red cells as normochromic.

– Variations in red cell size, e.g. microcytes, macrocytes, spherocytes, significant anisocytosis.

If normal in size, refer to the red cells as normocytic.

– Cells of abnormal shape or form, including pencil cells, sickle cells, target cells, fragmented

cells (schistocytes), tear drop cells, ‘bite’ cells, burr cells, cells showing rouleaux, significant poikilocytosis.

– Cells with inclusions, e.g. nucleated red cells, megaloblasts, cells containing Howell-Jolly cells containing malaria parasites, cells containing Bartonella organisms.

The degree of each type of red cell abnormality can be reported in plus signs as follows:

++++(very marked)

+++ (marked)

++(moderate)

+(slight but significant)

Nucleated red cells, target cells, sickle cells, megaloblasts, malaria parasites, Howell-Jolly

bodies, pencil cells, and other abnormal red cells can be reported as many, moderate numbers,

few, occasional. .

8 If the blood film has been made from EDTA anticoagulated venous blood, comment when platelet numbers appear greatly reduced or have an abnormal appearance .Perform a platelet

count when platelet numbers appear significantly reduced (check first that the blood sample is free

from clots) or increased.

Differential WBC reference range  Absolute

number Percentage

ADULTS

Neutrophils . . . . . 1.5–7.5 * 10^9/l (40–75%)

Lymphocytes‡ . . . 1.2–4.0 “ “ (21–40%)

Monocytes . . . . . 0.2–1.0 “ “ (2–10%)

Eosinophils . . . . . 0.02–0.6 “ “ (1–6%)

Basophils. . . . . . . 0.01–0.1 “ “ (0–1%)

CHILDREN (2–6 y)

Neutrophils . . . . . 1.5–6.5 * 109/l (20–45%)

Lymphocytes‡ . . . 6.0–8.5 “ “ (45–70%)

Monocytes . . . . . 0.1–1.0 “ “ (2–10%)

Eosinophils . . . . . 0.3–1.0 “ “ (1–6%)

Basophils. . . . . . . 0.01–0.1 “ “ (0.1–1%)

‡In an adult, lymphocytes are mainly of the

small type whereas in a child, large lymphocytes