What is a CBC Blood Test?

A Complete Blood Cell Count (CBC) measures the different cells in your blood. It looks at three main types:

• Red Blood Cells (RBCs): These cells carry oxygen from your lungs to the rest of your body and bring carbon dioxide back to your lungs to be exhaled. The CBC measures the number of red blood cells, as well as related components like:
  • Hemoglobin: The protein in red blood cells that carries oxygen.
  • Hematocrit: The proportion of red blood cells in your blood.
  • Mean Corpuscular Volume (MCV): The average size of your red blood cells.
  • Mean Corpuscular Hemoglobin (MCH): The average amount of hemoglobin in each red blood cell.
• White Blood Cells (WBCs): These cells are part of your immune system and help fight infections. The CBC counts the total number of white blood cells in your blood.
• Platelets: These small cell fragments help your blood clot, stopping bleeding when you get a cut. The CBC measures the number of platelets you have.

Beyond the counts, a CBC also looks at shape, size, and other characteristics of these cells. Those details help your doctor narrow down what's going on.

Key Components Measured in a CBC

• Red Blood Cell Count (RBC): Indicates the number of red blood cells in your blood.
• White Blood Cell Count (WBC): Shows the total number of white blood cells in your blood.
• Platelet Count: Reflects the number of platelets in your blood.
• Hemoglobin (Hgb): The amount of the oxygen-carrying protein in your red blood cells.
• Hematocrit (Hct): The proportion of your blood that is made up of red blood cells.
• Mean Corpuscular Volume (MCV): The average size of your red blood cells.
• Mean Corpuscular Hemoglobin (MCH): The average amount of hemoglobin in your red blood cells.
• Mean Corpuscular Hemoglobin Concentration (MCHC): The average concentration of hemoglobin in your red blood cells.
• Red Cell Distribution Width (RDW): A measure of the variation in the size of your red blood cells.

Each value is a clue. Low hemoglobin can suggest anemia. A high white blood cell count often points to infection. Your doctor reads them together, not in isolation.

What is a CBC with Differential?

A CBC with differential adds detail to the white blood cell count. Instead of just a total, it breaks WBCs into five subtypes. Each one fights different threats, so the breakdown gives your doctor much more information than the total alone.

Types of White Blood Cells Measured in a CBC with Differential:

• Neutrophils: These are the most common type of white blood cells and are your body's first line of defense against bacterial infections. They quickly respond to infections by destroying bacteria and other harmful organisms.
  • High Neutrophil Count: Often indicates a bacterial infection, inflammation, or stress.
  • Low Neutrophil Count: Could suggest a severe infection that has overwhelmed your immune system, or conditions like bone marrow disorders.
• Lymphocytes: These cells are essential for your immune system. There are two main types of lymphocytes: B cells and T cells. B cells produce antibodies to fight infections, while T cells destroy infected or cancerous cells.
  • High Lymphocyte Count: May indicate a viral infection or chronic inflammatory condition.
  • Low Lymphocyte Count: Can be seen in cases of severe illness, immune deficiency, or certain types of cancer.
• Monocytes: These cells are responsible for engulfing and digesting foreign substances in the body, including bacteria and dead or damaged cells.
  • High Monocyte Count: Often seen in chronic infections, autoimmune diseases, or certain cancers.
  • Low Monocyte Count: Rare and usually not a concern unless in combination with other abnormal counts.
• Eosinophils: These cells combat parasites and play a role in allergic reactions.
  • High Eosinophil Count: Commonly associated with allergic reactions, asthma, or parasitic infections.
  • Low Eosinophil Count: Typically not a concern as they naturally exist in lower numbers.
• Basophils: These are the least common white blood cells and are involved in allergic reactions and inflammatory responses.
  • High Basophil Count: Can indicate allergic reactions, chronic inflammation, or certain types of blood disorders.
  • Low Basophil Count: Usually not a concern as they are normally found in low numbers.

Why a CBC with Differential is Ordered

Your doctor orders it when they want a closer look at your immune system. It helps diagnose:

• Infections: By identifying whether the infection is bacterial, viral, or parasitic.
• Allergic Reactions: Through elevated eosinophil counts.
• Blood Disorders: Such as leukemia or lymphoma, by showing abnormal levels and types of white blood cells.
• Immune System Disorders: Indicated by abnormal levels of lymphocytes or neutrophils.

Breaking the WBC count into subtypes lets your doctor make more accurate diagnoses and tailor treatment.

Why is a CBC Ordered?

A CBC gets used for a lot of different reasons. Common ones:

Diagnosis

1. Anemia: Too few red blood cells, or not enough hemoglobin. Causes fatigue, weakness, and shortness of breath. CBC values pinpoint the type.
2. Infections: WBC count tells the doctor whether you're fighting one. High WBC usually means infection; very low WBC can mean a severe infection or immune issue.
3. Inflammation: Conditions like rheumatoid arthritis or lupus often shift CBC values.
4. Bleeding disorders: Low platelets suggest the blood isn't clotting properly, which can mean easy bruising or bleeding.

Tracking Existing Conditions

1. Chronic disease: If you have chronic kidney disease, heart disease, or diabetes, regular CBCs flag changes that may signal complications.
2. Chemotherapy: Chemo affects bone marrow, so CBCs are run often during treatment.
3. Medication side effects: Some drugs change blood cell counts. CBCs help your doctor catch trouble early.

Routine and Preventive Care

1. Annual checkups: A CBC gives a quick snapshot of overall health and can catch issues before symptoms show up.
2. Before surgery: Doctors often order a CBC pre-op to rule out anything that could complicate the procedure.

How to Prepare

Prep is simple, but a few notes:

Fasting and Diet

1. Fasting: A CBC on its own doesn't require fasting. If it's bundled with other tests (like a lipid panel), you may need to fast 8 to 12 hours. Follow what your doctor told you.
2. Diet: No special diet ahead of time. Eat a balanced meal and stay hydrated.

Medication

1. Tell your doctor what you take: Prescriptions, OTC drugs, and supplements can all affect blood cell counts.
2. Blood thinners: Make sure your doctor knows. They affect platelets and clotting.

Information for the Lab

1. Health conditions: Mention any chronic illness or recent infection.
2. Symptoms: If you've been dealing with fatigue, fever, or unusual bleeding, say so. It helps your doctor interpret the numbers in context.

Understanding Your Results

Your doctor will go through the report with you. Here's what the numbers mean.

Normal Ranges

Ranges vary slightly between labs, but typical adult reference ranges look like this:

• Red Blood Cell Count (RBC):
  • Men: 4.7 to 6.1 million cells per microliter
  • Women: 4.2 to 5.4 million cells per microliter
• White Blood Cell Count (WBC): 4,500 to 11,000 cells per microliter
• Platelet Count: 150,000 to 450,000 platelets per microliter
• Hemoglobin (Hgb):
  • Men: 13.8 to 17.2 grams per deciliter
  • Women: 12.1 to 15.1 grams per deciliter
• Hematocrit (Hct):
  • Men: 40.7% to 50.3%
  • Women: 36.1% to 44.3%
• Mean Corpuscular Volume (MCV): 80 to 100 femtoliters
• Mean Corpuscular Hemoglobin (MCH): 27 to 31 picograms per cell
• Mean Corpuscular Hemoglobin Concentration (MCHC): 32 to 36 grams per deciliter
• Red Cell Distribution Width (RDW): 11% to 15%

What Abnormal Results Mean

• Red Blood Cells (RBCs)
  • High RBC Count: This condition is known as polycythemia. It might indicate dehydration, living at high altitudes, or conditions that cause the body to produce too many red blood cells.
  • Low RBC Count: Known as anemia, this can result from blood loss, nutritional deficiencies (like low iron, vitamin B12, or folate), or bone marrow problems.
• White Blood Cells (WBCs)
  • High WBC Count: Called leukocytosis, it may indicate an infection, inflammation, an immune system disorder, or certain types of leukemia.
  • Low WBC Count: Known as leukopenia, it can be caused by severe infections, bone marrow disorders, autoimmune diseases, or the side effects of medications like chemotherapy.
• Platelets
  • High Platelet Count: Called thrombocytosis, this might be due to bone marrow disorders, inflammation, or certain cancers.
  • Low Platelet Count: Known as thrombocytopenia, this can result from bone marrow problems, autoimmune diseases, infections, or the use of certain medications.
• Hemoglobin (Hgb) and Hematocrit (Hct)
  • High Levels: Can be a sign of dehydration, smoking, living at high altitudes, or certain diseases.
  • Low Levels: Often indicate anemia, which could be due to various causes including nutritional deficiencies, chronic diseases, or bone marrow problems.
• Mean Corpuscular Volume (MCV)
  • High MCV: Indicates larger than normal red blood cells (macrocytic anemia), which can be caused by vitamin B12 or folate deficiency.
  • Low MCV: Indicates smaller than normal red blood cells (microcytic anemia), which can be due to iron deficiency or certain genetic conditions.
• Mean Corpuscular Hemoglobin (MCH) and Mean Corpuscular Hemoglobin Concentration (MCHC)
  • Abnormal Levels: Can provide further information about the type of anemia you might have, helping doctors pinpoint the cause.
• Red Cell Distribution Width (RDW)
  • High RDW: Indicates a large variation in the size of red blood cells, which can help diagnose different types of anemia.

What Can Affect Results

A few things can push your CBC numbers off without indicating real disease:

• Dehydration: Can falsely elevate RBC, hemoglobin, and hematocrit levels.
• Recent Illness or Infection: Can affect white blood cell counts.
• Medications: Certain drugs can impact blood cell counts, either increasing or decreasing them.
• Stress: Both physical and emotional stress can temporarily change blood cell counts.

If anything's abnormal, your doctor will usually order follow-up tests to find the cause. A low red blood cell count, for example, might mean an iron studies panel or vitamin B12/folate testing next.

Cost of Testing

CBC is included in many of the panels TeleTest offers. In Canada, provincial insurance like OHIP usually covers a CBC when it's medically necessary. Without insurance, it runs $15 to $20 at most labs.

Disclaimer: This blog post is intended for educational purposes only and should not be taken as medical advice. Always consult your healthcare provider for personal health concerns.