Pearls of Knowledge: WBC and the Differential

Lab Values: WBC and the Differential 

Pearls of Knowledge          © BrainyNurses.com

There are many conditions that will alter the white blood cell count. The most common cause of an elevation is a bacterial or parasitic infection or any type of an inflammatory disorder. Some of the immune system and thyroid disorders may be implicated. Select drugs, such as glucocorticoids will also elevate the count. Leukemia will elevate the count; however, the cells are dysfunctional, and a risk for infection is present.

A low white blood cell count is often caused by viral infections, severe infections due to depletion of the cells, congenital disorders, damage to the bone marrow, autoimmune disorders, and medications such as anti-infectives or chemotherapy that suppress the bone marrow. Leukopenia is white blood cells < 1,000 cells/mm3. Agranulocytosis is a severe decrease of < 200 cells/mm3.

Types of white blood cells 

There are five different types of white blood cells. In analysis, the five are given a percentage of the total count. A normal count is 5,000-11,000 cells/mm3. In some conditions, such as pregnancy, it is normal to have a higher elevation.

• Neutrophils (55-70%)           
• Lymphocytes (20-40%)
• Monocytes (2-8%)
• Basophils (0.5-1%)
• Eosinophils (1-4%)

An analysis of the percentages can help determine what type of infection is present. Cultures will then follow to determine the organism(s).

Antistreptolysin O (ASO) titer 

The ASO titer measures antibodies produced after exposure to group A streptococcus bacteria. The result will be positive for months after the exposure. When the test is ordered an immediate result is obtained and treatment can be started without having to wait for the results of cultures.

Select disorders where it will be positive

• Strep throat
• Endocarditis
• Scarlet fever
• Rheumatic fever
• Glomerulonephritis

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