WBC Lab Tests: Topic 1

Question 1

what is the WBC count?

Answer 1

the number of white blood cells per mm3 of blood

Question 2

how are WBC counted?

Answer 2

by an automated hematology analyzer or by viewing a blood smear

Question 3

what are the 5 types of WBC?

Answer 3

1. basophils
2. monocytes
3. eosinophils
4. neutrophils
5. lymphocytes

“the differential” WBC count

usually reported as % values which are used to calculate the absolute numbers of individual WBC types

Question 4

how do automated analyzers work?

Answer 4

sort blood cells into into groups based on their size and internal complexity

the machine sorts the cells into groups, and counts the number of cells in each group; works MOST of the time

ex. monocytes are big and simple with just a big nucleus
ex. neutrophils are medium sized and are complicated with lots of granules and segmented nucleus

Question 5

what do you do if something on the complete blood count (CBC) looks unusual, or if you are concerned about the morphology of a particular type of cell?

Answer 5

since the automated analyzer can’t “see” the cells like a human can, sometimes things get put in the wrong category. Giant platelets, for example, might be counted as red blood cells, or malignant blasts might be put in the lymphocyte group

if something on the complete blood count (CBC) looks unusual, or if you are concerned about the morphology of a particular type of cell, it’s important to look at the blood smear the old- fashioned way, using a microscope.

Question 6

what does the differential count measure?

Answer 6

The differential measures the relative amounts of the five major white blood cell types in blood: basophils, monocytes, eosinophils, neutrophils, and lymphocytes

MAKE SURE YOU USE THE ABSOLUTE COUNT THOUGH!! Just because the % is janky, doesn’t mean the actual number of a certain WBC is messed up

Question 7

what is the normal WBC count?

Answer 7

4,500 – 11,000 cells/mm3

Question 8

Which white blood cell type makes up the largest percentage of the total WBC?

Answer 8

neutrophils

57-67%

Question 9

what is the WBC differential? AKA which types of WBC are most/least prominent?

Answer 9

neutrophils > lymphocytes> monocytes > eosinophils > basophils

neutrophil: 57-67%
lymphocytes: 25-33%
monocytes: 3-7%
eosinophils: 1-3%
basophils: <1%

Question 10

Which is a better estimate of the true number of white blood cells: absolute counts or percentages?

Answer 10

Absolute counts. Always.

Question 11

how are WBC counts changed when there’s an infection?

Answer 11

infections usually produce high WBC = leukocytosis

Question 12

what can the differential WBC count tell you about an infection?

Answer 12

differential count can provide important clues as to the type of infection

bacterial infections typically cause the neutrophil count to go up, and viral infections cause the lymphocyte count to go up

Question 13

how do bacterial infections effect the WBC differential?

Answer 13

cause the neutrophil count to go up

Question 14

how do viral infections effect the WBC differential?

Answer 14

cause the lymphocyte count to go up

Question 15

what causes changes in the WBC and differential?

Answer 15

1. bacterial infections
2. viral infections
3. drug reactions (drug induced eosinophilia)
4. immune conditions (HIV)
5. malignancies (acute lymphoblastic leukemia)

Question 16

what happens in acute lymphoblastic leukemia?

Answer 16

malignant lymphoblasts proliferate in the bone marrow, crowding out normal hematopoietic precursors

as malignant cells pour into the blood, the WBC skyrockets, but the number of normal WBCs often drops to a dangerously low level