A differential blood count is a blood test to check your white blood cell levels, which can indicate the presence of infection, disease, or an allergic reaction. Your doctor might order it as part of routine testing or to check for infections and other problems.
There are various types of differential blood counts, including manual and complete blood count (CBC) with differential.
A differential blood count does not measure the amount of white blood cells in your blood; rather, it looks at the percentages and numbers of various types of white blood cells and looks for irregular cells. Your doctor might also order an ordinary white blood cell count for a better overall picture.
White blood cells are also called leukocytes. The different types include:
- Lymphocytes. These are your B cells and T cells, which make antibodies to help you fight infections.
- Neutrophils. These cells kill invaders like bacteria by traveling to the infection site and releasing enzymes. Neutrophils are the most common white blood cell.
- Monocytes. A monocyte helps break down and remove dead cells and bacteria.
- Basophils. These cells release a chemical called histamine to help fight allergic reactions. They also fight infection and inflammation.
- Eosinophils. These cells release enzymes that fight and kill cancer cells and parasites. They also help with allergic reactions and asthma attacks.
What Is a Manual Differential Blood Test?
Most differentials are automated tests done with special equipment. If something unusual shows up in an automated test, the lab might manually check the sample. This is called a manual differential. It can also help look for unusual cells and young cells called a band.
What Is a CBC with Differential?
Sometimes, a differential is also done with a complete blood count, which is called a CBC with differential. This test measures the specifics of your white blood cell count, plus all your other blood cell levels, including red blood cells and platelets.
Why Do You Need a Manual Differential Test?
Your doctor will order a differential blood count to monitor your health during some types of treatment, as a routine check-up, or if they think you have a problem with your white blood cells. These problems can happen for lots of different reasons.
In other cases, you might have something in your body that is destroying your white blood cells faster than you can make them. If your white blood cell count is too low, you have a higher chance of getting an infection because you don’t have enough immune cells to help you fight off invaders. This often happens with diseases like HIV, or chemotherapy and radiation treatment for cancer.
Other diseases that affect your blood cell levels include:
- Blood cancer
- Autoimmune diseases
- Allergic reaction
- Liver disease
- Spleen disease
Differential tests are also a part of routine newborn screening. After your baby is born, your doctor will run some blood tests to check for blood cell disorders. These blood tests can help with early diagnosis and make sure your baby gets treatment.
What Is the Normal White Blood Cell Count Range?
A normal white blood cell count means that your different white blood cells fall within the average percentage. Normal white blood cell count range can vary by lab, but generally is as follows:
- Neutrophils, 40%-70% of the total count
- Lymphocytes, 22%-44%
- Monocytes, 4%-11%
- Eosinophils, 0%-8%
- Basophils, 0%-3%
- Chemotherapy treatment
- Radiation treatment or exposure
- Severe bacterial infection
- Viral infection
- Steroid use
- High stress
- Eclampsia, a condition in pregnancy that causes seizures and coma
- Thyroid disease
- Rheumatoid arthritis
- Rheumatic fever
- Viral infection
- Bacterial infection
- Lymphocytic leukemia
- Parasite infection
- Allergic reaction
Keep in mind that a high or low white blood cell count doesn’t always mean you have a health problem. Some factors, like intense exercise, drinking alcohol, and even your diet, can affect your results. If you have abnormal results, your doctor might order more specific tests.