Complete Blood Count (CBC)

A complete blood count (CBC), sometimes called CBC with differential or full blood count, is a common test which tests for a wide range of disorders. The test usually involves a lab technician drawing blood, usually from the inside of the elbow. It is quick and usually fairly painless.

After a CBC, a hematology analyzer determines if there are any increases or decreases in white blood cell, red blood cell, and platelet counts. Normal complete blood count ranges depend on age and sex. A CBC can help diagnose a broad range of conditions, including anemia, infections and cancer.

A complete blood count test is usually ordered by doctors to diagnose a suspected medical condition, to monitor a medical condition, or to monitor medical treatment.

A CBC is helpful for evaluating patients’ health. A CBC is also often done as a part of a routine medical examination to help the doctor get a clear picture of the patient’s health.

CBC tests analyze red blood cells, white blood cells, and platelets.

Red blood cells are the most common blood cell, and contain hemoglobin, an important protein for transporting oxygen around the body.

White blood cells are cells found in the blood that fight against viruses, bacteria and parasites. Platelets are tiny cell fragments that circulate through the body and make blood clot normally.

Red blood cell count includes examining hemoglobin and hematocrit. If the red blood cell, hemoglobin, or hematocrit counts are low, this indicates anemia. If these levels are higher than normal, this can indicate a medical condition such as polycythemia vera or heart disease.

If the white blood cell count is high, this might be because of an infection or inflammation. However, it can also indicate problems with the bone marrow or immune system, or a reaction to a medication. In contrast, a low white blood cell count may indicate an autoimmune disorder destroying white blood cells, white blood cell production issues, or even cancer.

An abnormally high or low platelet count often indicates a medical condition. It can also be due to side effects from medication.

A CBC is a complete blood count, and offers a complete overview. This is why they are such a common test. Some of the most common diseases a CBC detects include anemia, autoimmune disorders, bone marrow disorders, dehydration, infections, inflammation, leukemia, lymphoma, myeloproliferative neoplasms, myelodysplastic syndrome, sickle cell disease, thalassemia, nutritional deficiencies (e.g., Iron, B12 or folate), and cancer that has spread to the bone marrow.

Depending on the condition, CBC results often will not result in a diagnosis. Follow up tests may be done to properly determine the condition. What these tests will include depends on the abnormalities found, medical history, and the suspected condition.

If you have had a CBC done recently, you may need help with the interpretation of full blood count. Blood is made of two components - plasma and cells. Plasma is the liquid the cells are supported by. A CBC is responsible for testing the cells. There may be several terms on the results you are not familiar with. The normal ranges listed below are for a healthy adult. Ranges vary depending on sex, age, and other conditions.

Hemoglobin is a protein that carries oxygen around the body. Its normal range is 13.5 to 17.5 g/dL for men, and 12 to 15.5 g/dL for women. Hematocrit indicates the proportion of the count that are red blood cells. A normal range is a 0.33 to 0.42 ratio.

MCV is mean cell volume, and should be 74 to 87 fL. MCH is the amount of hemoglobin per blood cell, and a normal range is 24 to 29 pg.

WBC stands for white blood cells, and indicates the total number of white blood cells in the blood. A White blood cell normal range is 4.5 to 12 x 109/L.

Neutrophils, lymphocytes, monocytes and eosinophils are all types of white blood cells. Their absolute counts should be:

• neutrophils: 1.5 to 8 x 109/L
• lymphocytes: 1.4 to 5.7 x 109/L
• monocytes: 0.3 to 1 x 109/L
• eosinophils: 0 to 1 x 109/L
  

A normal platelet count is between 150 and 475 x 109/L.

If you’re concerned or unsure about any of your CBC results, you can ask your doctor.

A CBC with differential is also known as a blood differential test, white blood differential count, or leukocyte differential count. It may be performed as part of a CBC test or as a follow-up to a CBC test that reveals you have an abnormally high white blood cell count.

While a CBC test measures the total number of red blood cells (erythrocytes), white blood cells (leukocytes), platelets, hemoglobin, and hematocrit, a CBC with differential goes one step further to identify and count the number of each type of white blood cell in your blood.

Humans have five different types of white blood cells in their blood. These are the neutrophils, eosinophils, basophils, monocytes, and lymphocytes (T cells and B cells). A CBC with diff checks if there are any abnormalities in any of the white blood cells.

The CBC differential results are typically recorded as a percentage.

Real time CBC testing produces the following normal CBC differential ranges[1]:

• Neutrophils: 40% to 60%
• Lymphocytes: 20% to 40%
• Monocytes: 2% to 8%
• Eosinophils: 1% to 4%
• Basophils: 0.5% to 1%
• Band (young neutrophil): 0% to 3%
  

Abnormal results of a CBC differential:

Certain medical disorders can cause your bone marrow to produce abnormal counts of white blood cells.[1:1][2]

Increased number of neutrophils: Your bone marrow may make a higher number of neutrophils if you have a bacterial infection or are experiencing acute stress or trauma.

Increased number of eosinophils: Allergies can cause an increased number of neutrophils. Also, if you have Addison disease, collagen vascular disease, parasitic infection, or cancer, you may have increased eosinophil production.

Increased number of lymphocytes: Your bone marrow may produce excess lymphocytes if you have a viral or chronic bacterial infection, lymphocytic leukemia, or multiple myeloma.

Increased number of monocytes: This can be due to chronic inflammatory disease, leukemia, parasitic infection, tuberculosis, or viral infection.

Increased number of basophils: This can result as a side effect of splenectomy, allergic reaction, chronic myelogenous leukemia, collagen vascular disease, myeloproliferative diseases, and chickenpox.

Rapid CBC for clinical trials and research are important, especially in the study of various cancer therapies.

Oncology drugs typically result in bone marrow toxicity that can destroy the production of blood cells. During clinical trials, the participants’ complete blood count should be checked frequently to ensure that the therapeutic drug in the trial is not destroying the body’s blood cells excessively.

One example of cancer therapy that is toxic to the bone marrow is 131I therapy for thyroid cancer, although the adverse effects are rarely life-threatening. Clinical researchers showed that 131I therapy affects the complete blood count of patients, although the benefits of the therapy outweigh the hematological risks.[3]