Differential blood test: Uses, procedure, and results

The results provide information about the condition of a person’s immune system and how it responds to diseases and other threats.

In this article, learn more about how doctors use the differential blood test and how they interpret its results.

Who needs a differential blood test?

A doctor will often order this test when trying to confirm a diagnosis.

They may be looking for signs of an acute illness, such as the flu or a urinary tract infection.

Or, they may be checking for a chronic condition, such as an autoimmune disorder or one that affects the bone marrow.

The bone marrow is responsible for producing white blood cells, so changes in white blood cell counts can indicate how well the bone marrow is functioning.

A doctor may order a differential blood test if a person has symptoms, such as:

  • body aches
  • chills
  • fever
  • a headache
  • pain, particularly in the bones

While a differential blood test can indicate problems with the white blood cells, it will not be the only test that doctors use to make a diagnosis.

To perform the test, doctors draw a blood sample from a vein in the arm or finger. When testing an infant, a doctor will draw blood from the heel.

There is no need to fast or make any special preparations for a differential blood test.

While the results of a differential blood test give information about all five types of white blood cell, a doctor is usually focusing on just one or two types.

Depending on the type of cell, high or low levels can indicate different issues, such as:


  • High: A basophil count can point to certain types of leukemia, including chronic myeloid leukemia. A high count can also indicate that a person has severe allergic reactions. People with inflammatory disorders, such as rheumatoid arthritis or ulcerative colitis, may also have high basophil counts.
  • Low: A low basophil count does not typically suggest a medical condition. However, stress, allergic reactions, steroid use, and hyperthyroidism can each cause a basophil count to be low.


  • High: A high eosinophil count tends to result from an allergic reaction, such as asthma, eczema or a reaction to a medication. Inflammatory disorders, such as celiac disease or inflammatory bowel disease (IBD), can also cause high eosinophil levels.
  • Low: Eosinophils are usually present in such low quantities that low readings do not tend to indicate issues. However, stress or steroid use can also cause an eosinophil count to be low.


  • High: A high lymphocyte level can indicate an acute viral infection, such as chicken pox, herpes, or hepatitis. Or, a lymphocyte count may be high because of a bacterial infection, such as tuberculosis or pertussis, or a condition such as lymphocytic leukemia or lymphoma.
  • Low: A low lymphocyte level can point to an autoimmune disorder, such as lupus or rheumatoid arthritis. The presence of HIV, tuberculosis, hepatitis, or the flu can also cause a lymphocyte count to be low.


  • High: A high monocyte count can result from a chronic infection, such as tuberculosis, or a fungal infection. The presence of a condition such as endocarditis (bacterial inflammation of the heart), IBD, monocytic leukemia, juvenile myelomonocytic leukemia, scleroderma, or rheumatoid arthritis can also cause a count to be high.
  • Low: Most doctors do not consider a single low monocyte count to be significant. However, low monocyte results on several tests can indicate hairy cell leukemia or bone marrow damage.


  • High: A high neutrophil level can indicate an acute bacterial infection, inflammation, tissue death (such as after a heart attack), stress on the body, or chronic leukemia. A level may also be high because a person is in the last trimester of pregnancy.
  • Low: A neutrophil count may be low after an adverse drug reaction or chemotherapy treatments. Illnesses, such as myelodysplastic syndrome, autoimmune disorders, bone marrow cancers, and aplastic anemia can also cause low neutrophil counts.


A differential blood test is one of many lab tests that a doctor can use to confirm a diagnosis of an infection or illness.

Values can vary from lab to lab, and a person should carefully review their results with the doctor.

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