Decoding A CBC Test: What a Complete Blood Count Can Reveal About Your Health
- Elizabeth Priest
- Sep 25
- 9 min read
Why It is Important to Run a CBC with Differential Test, and Why You Should Care About Yours
Intro and What Is a Complete Blood Count (CBC)
With all of my new clients' lab recommendations, I include a simple but powerful test: the Complete Blood Count with Differential (also known as a CBC with diff). It's one of the most basic blood tests you can get, but it can reveal a surprising amount about your overall health.
When trying to identify the origin of new symptoms, monitor a chronic condition, or prevent future health problems, a complete blood count (CBC) test is a good starting point for identifying health issues such as anemias, infections, autoimmune diseases, blood disorders, and even cancers.
I don't just run this test once. It is important to reassess a CBC with diff often because it helps me track progress and catch subtle shifts before they become bigger problems, and it also helps monitor therapies/treatment.
The results of a CBC can hint at the causes behind acute problems and chronic, low-lying problems such as inflammation or infection. They can also reveal markers of vascular damage and decreased blood flow that could indicate a heightened risk of cardiovascular and metabolic diseases. The earlier you catch these warning signs, the more time you have to start lifestyle changes and, if necessary, medications to reverse course.
Why CBCs Are Ordered
Routine health screenings to catch early anomalies
Symptom investigation, such as fatigue, fever, bruising, etc.
Monitoring ongoing conditions, e.g., cancer, chronic infections such as EBV, parasitic infections, allergy symptoms, pregnancy, medication effects, and more.
The human body runs on blood. Blood flows through your body, performing life-sustaining functions. Approximately 45% consists of red blood cells (RBC), white blood cells (WBC), and platelets.
Red blood cells, the most common type of blood cell, deliver oxygen to the other cells. While white blood cells fight infection. Platelets stick together to form clots that patch holes in blood vessels. About 55% of blood is plasma, a yellowish fluid full of proteins, sugars, and fat particles.
A CBC provides an account of the red blood cells, white blood cells, and platelets in your blood, offering a glimpse into their functioning. This is important because problems with your blood can affect the organs it supplies, such as your heart and brain.
The results of a CBC with diff include a lot of data. Here's what you need to know about what all those numbers mean.
Components of the CBC and What They Indicate
What red blood cells can tell us
In the CBC test, Red Blood Cells (RBCs) are simply the total number of erythrocytes found in a cubic millimeter of blood. Think of this as the population of red blood cells in the blood.
Functional range: 4-4.5 u/L
Red blood cells, also called erythrocytes, store and carry oxygen from your lungs to your tissues with the help of the vascular system and the heart. Red blood cells release oxygen into cells within your tissues, which use the oxygen to make energy. Without enough oxygen, these cells and tissues can function less efficiently and ultimately die.
In the CBC, we are looking for the total number of RBCs. If the total number of RBCs is depressed or elevated, it can indicate various conditions, ranging from dehydration to nutrient deficiencies to different types of cancer.
Within the CBC, we are also evaluating the markers of RBC characteristics. There are three key markers in a serum test that indicate anemia: red blood cells, hemoglobin, and hematocrit. These three measures indicate how efficiently the blood carries oxygen for delivery to the rest of the body and can help detect different types of anemia. At the most basic level, anemia is a condition in which you don't have enough healthy red blood cells or hemoglobin to carry adequate oxygen to the body's tissues. It develops for many different reasons: when iron stores in the body and bone marrow have become depleted; when there is insufficient B12 or folate to properly mature RBCs; or when there is any kind of dysfunction in the process of creating and then recycling red blood cells.
There are hundreds of kinds of anemias, ranging from iron-deficient anemia to B-vitamin deficiency to normocytic normochromic anemia to anemia of chronic disease, among others. Consequently, further testing is necessary to determine the specific type of anemia present.
Here's a fun fact:
RBCs are "born big" and gradually get smaller over their ~120-day
lifespan. They need specific nutrients along the way — iron, folate, B12, copper — to mature properly and carry oxygen to your tissues. When something's off in these markers, it often ties back to nutrient deficiencies, gut health, or chronic inflammation.
Hemoglobin (Hb) is an iron-rich protein in red blood cells. Its primary role is to bind to oxygen and deliver it to tissues. Then, hemoglobin picks up carbon dioxide, a waste product, and carries it back to your lungs so you can exhale it.
Functional range: 13-15 g/dL
Hematocrit (Hct) is the percentage of red blood cells in your blood. It often trends in the same direction as red blood cell count, but not always. Hematocrit indicates how many red blood cells you have in the context of other blood fluids.
Functional range: 40-45%
Mean corpuscular volume (MCV) is the measurement of the average size of red blood cells. It indicates whether the red blood cell size appears normocytic (normal-sized), microcytic (too small), or macrocytic (too large). An increase or decrease in this marker will help you determine the type of anemia present, if anemia is the problem. We can also use this marker to monitor vitamin deficiencies. For example, a lack of iron and hemoglobin can stunt the growth of red blood cells, while vitamin deficiencies (particularly folate and B12) can disrupt red blood cell division, causing them to stay oversized, which impairs their functioning.
Functional range: 82-89 fL
Platelet count: Platelets are tiny, disc-shaped cells that originate in bone marrow. They flock to wounds and clump together to form clots, sealing the injured area so it can heal without further damage. Platelets can also interact with other immune cells and become overactivated in some inflammatory diseases, possibly contributing to joint inflammation.
Functional range: 175- 250 x103/uL
What white blood cells can tell us
White blood cells (WBC), also known as leukocytes, are a type of blood cell that lack hemoglobin, making them colorless. They are larger in size than red blood cells and are found throughout the body, including the blood and lymphatic system.
There are a number of different types of white blood cells, each with a specific function and role in combating invaders.
As a critical part of your immune system, white blood cells fight infection. Your white blood cells (WBCs) are the "foot soldiers" of your immune system. When you get sick, your body makes more white blood cells to battle bacteria, viruses, and other unwelcome guests. Approximately 1% of blood is composed of white blood cells. WBC functional range: 5-7 u/L
When we see high or low total WBC counts, it can indicate an active infection (acute or chronic), immune suppression, inflammation, or other stressors. We cannot just look at the total amount of WBC; we have to look further. This is where the "with differential" part comes in.
Most conventional doctors order a CBC, but they often overlook (or skip discussing) the WBC differential —the breakdown of your white blood cells into different types. The WBC is the armed forces, with different troops. From a functional perspective, the breakdown of the differential is gold.
Neutrophils: In a healthy person, neutrophils are the most abundant type of white blood cells. The Functional range is: 40-60%
They are short-lived and highly motile. Neutrophils are your first line of defense against infections from bacteria, fungi, and other germs. Neutrophils are a type of phagocyte and are usually found in the bloodstream. They rush to the site of infection or inflammation, and protect the body by ingesting harmful foreign particles, bacteria, and dead or dying cells. Neutrophils are like Pac-Man, eating and destroying pathogens and waste products.
Neutrophils are also one of the first responders of inflammatory cells to migrate towards the site of inflammation. They travel throughout the body via blood vessels in response to signals from cytokines.
Lymphocytes: Lymphocytes are stored in Lymph nodes, which are found in various areas of the body. Lymph fluid is filtered through the lymph nodes, where any foreign organisms, such as bacteria, are trapped and attacked by the lymphocytes. The primary function of the lymph nodes is to combat pathogens, such as bacteria and cancer cells. They do this by removing foreign particles from the body, creating antibodies, producing lymphocytes, and housing macrophages, which engulf and digest cellular debris and foreign substances.
Lymphocytes are a type of white blood cell that plays a crucial role in the immune system. Three types of lymphocytes develop from lymphoid stem cells: B cells, T cells, and natural killer cells.
It is important to view lymphocytes in conjunction with neutrophils, looking for a pattern. They second in total numbers to neutrophils. An example would be if there is a normal total WBC count but neutrophils are low and lymphocytes are elevated, which can indicate a chronic infection, often of viral etiology.
Functional range: 24-44%
Neutrophil to Lymphocyte ratio (NLR): Looking for a 2 to 1 ratio with 2 Neut to 1 Lymph.
Monocytes are the largest type of white blood cells, and they serve as the body's second line of defense against infection. Monocytes patrol for germs and head toward whatever mess they find. When they encounter infected or inflamed tissue, they can divide and differentiate into two new cell types: macrophages and dendritic cells, which enable them to mount an immune response.
Macrophages are phagocytes (think of them as Pac-Men), and they are often referred to as scavengers or antigen-presenting cells because they pick up and ingest foreign materials, then present these antigens to other cells. The other type of monocyte is called a dendritic cell. Dendritic cells function as antigen-presenting cells.
Functional range: 1-7%
Eosinophils are white blood cells that are primarily found in tissues and not in the blood. Their primary job is to mobilize against triggers of allergies and asthma, as well as infections, tissue injuries, and tumors, and to destroy antigens and antibodies. Eosinophils contain histamine, making them the reactive white blood cells. When out of balance, it is more common to see eosinophils elevate than depress. When we see this, it's a strong indicator of intestinal parasites and/or allergies and sensitivities to triggers from environmental agents (ie, pollens, grasses, mold, even food). Because Eosinophils are primarily found in the tissues, an increase in this marker indicates an issue in the tissues.
Functional range: 1-3%
Basophils play a leading role in many specific kinds of inflammatory reactions, particularly allergic reactions. When you eat, breathe in, or touch an allergen, basophils migrate to your gut, lungs, or skin to release histamine, a vasodilator which promotes blood flow to tissues, spurring inflammation. Basophils also contain anticoagulant properties, which prevent blood from clotting too quickly.
Functional range: <1%
Common Abnormal Findings & What They Suggest From a Functional Lens
Low hemoglobin/RBC/Hct: Anemia (like iron/B12 deficiency or from internal bleeding
High RBC/Hgb/Hct: Most often due to dehydration, this condition could also be caused by respiratory distress, sleep apnea, or, in rarer cases, Polycythemia.
Low WBC: Immune-compromised/ suppression, chronic infections, cancer, can be a clue to an increased heavy metal burden in the body.
High WBC: Acute infection, inflammation, parasitic infection, cancer, stress
Even if your total White Blood Cell (WBC) count is "normal", the ratios between these different types can reveal hidden patterns. For example:
Low neutrophils + elevated lymphocytes: may suggest a chronic, low-grade viral infection (like EBV or CMV), overall increased total body burden.
Elevated eosinophils can indicate the presence of intestinal parasites, allergies, or mast cell activation syndrome (MCAS).
High Basophils + high monocytes + high eosinophils = "poor man's parasite test" and can indicate gut dysbiosis, and/or leaky gut.
Increases in monocytes or basophils can give additional clues about inflammation or immune reactivity.
The CBC doesn't tell us exactly which infection or trigger is present, or which anemia is at play; that's where more targeted functional testing comes in, but it can help us understand where to look next (ie, stool testing, food sensitivity testing, chronic viral assessments, low-lying bacterial infections such as MARCoNS, Lyme, etc.)
Why I Use This Test
The CBC with differential is inexpensive, quick, and non-invasive. From a functional lens, it's like having a sneak peek into your body's internal strategy, how your immune system is allocating its resources, and how well your oxygen transport system is running.
When we take a closer look at the biomarkers in the CBC with differential, we can see small shifts in the numbers, which can indicate that your body is quietly working hard behind the scenes. When we pair the CBC patterns with a client's history, symptoms, and other laboratory results, it often provides the "first breadcrumb" that leads the path to uncovering deeper root causes. With proper nutrition and lifestyle support, we can work to modulate the immune system and restore it to balance.
If you're ready to take charge of your health and gain valuable insights into your underlying conditions, working with me can make all the difference. This simple test could be part of your first step towards optimizing your health or gaining a fresh perspective on your chronic health concerns. When you work with me, I can help identify the key areas to focus on for improved well-being and develop a tailored approach to enhance your overall health. Don't wait, reach out today, and let's begin your journey to better health!
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