In today’s post, I will be going over the complete blood count (CBC), one of the most commonly ordered blood tests in clinical practice. It’s good for every cancer patient to understand the basics of this test. It helps to evaluate your overall health and can diagnose a wide variety of disorders. It will also help in monitoring existing medical conditions and the effects of treatments. With all this knowledge, you can ask questions and make better decisions when it comes to your care.
In this comprehensive overview, I will break down each component of the CBC in detail, including the physiological significance of the values and the clinical relevance of abnormal results. Stay to the end where I will tell you about a simple ratio you can calculate on your own that has major clinical significance.
A CBC includes the following components
- Red Blood Cell Count (RBC)
- Hemoglobin (Hb)
- Hematocrit (Hct)
- Mean Corpuscular Volume (MCV)
- Mean Corpuscular Hemoblogin (MCH)
- Mean Corpuscular Hemoglobin Concentration (MCHC)
- Red Cell Distribution Width (RDW)
- White Blood Cell Count (WBC)
- White Blood Cell Differential Count
- Platelet Count
- Mean Platelet Volume (MPV)
RED BLOOD CELL COUNT
The RBC count measures the number of red blood cells present in a given volume of blood, typically expressed as millions of cells per microliter (cells/µL). RBCs, or erythrocytes, are responsible for transporting oxygen from the lungs to the tissues and returning carbon dioxide from the tissues to the lungs. RBCs contain a protein called hemoglobin (Hb), which binds to oxygen in the lungs and releases it in the tissues.
Normal Range
- 4.2–5.4 million cells/µL
Clinical Significance of an Abnormal RBC Count
- A low RBC count indicates anemia, which may be caused by various conditions such as iron deficiency, vitamin B12 or folate deficiency, chronic disease, blood loss or bone marrow suppression. In addition, chronic kidney disease and cancer treatments can also cause anemia. Nutrient deficiencies may be caused by malabsorption in the gut and/or low intake (i.e. vegan or vegetarian diets).
- An elevated RBC count, called polycythemia, can occur due to chronic hypoxia (low oxygen levels) from lung disease or living at high altitudes, genetic bone marrow disorders like polycythemia vera, or dehydration.
HEMOGLOBIN (Hb)
Hemoglobin is the iron-containing protein in RBCs responsible for oxygen transport. The hemoglobin test measures the amount of hemoglobin in the blood. Hemoglobin binds to oxygen in the lungs and releases it in tissues with lower oxygen levels. It also carries carbon dioxide from tissues back to the lungs for exhalation.
Normal Range
- 12.1–15.1 g/dL
Clinical Significance of Abnormal Hemoglobin
- Low hemoglobin levels typically reflect anemia. The most common cause is iron deficiency as iron is necessary for hemoglobin production. However, cancer patients often have plenty of iron, and a low Hb may suggest bone marrow damage most often caused by treatments. Other causes include, vitamin B12 and folate deficiency, chronic diseases, inflammatory diseases or blood loss.
- If you have tests showing iron deficiency anemia on the CBC, it is important to check ferritin (iron level) and iron storage capacity tests to see if iron deficiency is really a problem.
- High hemoglobin levels can occur in response to polycythemia vera (a condition of excessive RBC production in the bone marrow, most often genetic), chronic hypoxia or dehydration.
HEMATOCRIT (HCT)
The hematocrit is the percentage of blood volume that is occupied by red blood cells. It is closely related to the RBC count and hemoglobin levels. The hematocrit is used to assess the blood’s oxygen carrying capacity.
Normal Range
- 36-48%
Clinical Significance of Abnormal Hematocrit
- Low hematocrit is often seen in anemia and suggests a reduction in the oxygen carrying capacity of the blood. The causes of this are the same as for low red blood cells. See my notes above on iron deficiency.
- A high hematocrit, as with hemoglobin, can be due to dehydration or low oxygen conditions.
MEAN CORPUSCULAR VOLUME (MCV)
The mean corpuscular volume measures the average volume of a red blood cell. It is expressed in femtoliters (fL). Fun fact, a femtoliter is one quadrillionth of a liter! The MCV helps classify anemia into different categories based on the size of the RBCs. These are microcytic (smaller than normal), normocytic (normal size) and macrocytic (larger than normal).
Normal Range
- 80-100 fL
Clinical Significance of Abnormal MCV
- Low MCV indicates microcytic anemia. This is typically due to iron deficiency. It occurs when there is insufficient iron to produce hemoglobin. This can be due to inadequate dietary intake, poor absorption or blood loss. In cancer patients, malabsorption and stress can lead to low levels of vitamin B6, zinc and magnesium, which can cause low MCV (85-89). Chronic inflammatory conditions, infections or cancer can lead to microcytic anemia. The iron metabolism is disrupted and iron is not efficiently utilized for RBC production. Exposure to lead can also cause this as well as some genetic conditions. As with low hemoglobin, it will be important to get other tests to determine if you actually have low iron stores (ferritin).
- High MCV is where RBCs are larger than normal, called macrocytosis. This is commonly seen with B12 and folate deficiency, anemia, liver disease and hypothyroidism. Chemotherapy and some drugs like metformin can cause this. Certain bone marrow disorders and methylation issues (see more below) can also cause this abnormality.
MEAN CORPUSCULAR HEMOGLOBIN (MCH)
The mean corpuscular hemoglobin measures the average amount of hemoglobin in each red blood cell. MCH helps determine the hemoglobin content in individual RBCs and is used to further characterize types of anemia.
Normal Range
- 26-34 picograms (pg)
Clinical Significance of Abnormal MCH
- Low MCH is also called hypochromia. As with MCV, low levels of vitamin B6, zinc and magnesium can cause this. The most common cause is iron deficiency anemia. Other chronic conditions, like kidney disease and cancer can affect hemoglobin production and lead to low MCH as well.
- High MCH, called hyperchromia, is most often related to vitamin B12 and folate deficiencies, anemia and liver disease or hypothyroidism.
MEAN CORPUSCULAR HEMOGLOBIN CONCENTRATION (MCHC)
The MCHC measures the average concentration of hemoglobin in a given volume of red blood cells. MCHC reflects how concentrated the hemoglobin is within the RBCs and helps assess whether the RBCs are under-filled or overfilled with hemoglobin. It helps in diagnosing and classifying different types of anemia.
Normal Range
- 32-36 g/dL
Clinical Significance of Abnormal MCHC
- Low MCHC is often associated with hypochromic anemia caused by iron deficiency. This is when the RBCs contain less hemoglobin. Nutritional deficiencies, especially vitamin B6, zinc and magnesium can cause this. Other causes include, anemia of chronic disease, chronic inflammation, trouble absorbing iron, kidney disease and lead exposure.
- High MCHC is most commonly associated with autoimmune hemolytic anemia. This is where the immune system mistakenly attacks and destroys RBCs. Vitamin B12 deficiency, other autoimmune conditions (i.e. lupus), liver disease, hypothyroidism and lymphoma can also cause this abnormality. Chemotherapy and radiation can alter the RBCs and impact the MCHC.
High MCV >90/MCH >30/MCHC >30 are clues to deficient levels of vitamins B12, B6 and folate and methylation problems. DNA methylation is a chemical modification that plays an important role in the regulation and expression of genes. In cancer patients DNA methylation can be disrupted promoting cancer growth.
RED CELL DISTRIBUTION WIDTH (RDW)
The RDW measures the variation in size of red blood cells, also called anisocytosis. It is expressed as a percentage. Normally RBCs are very similar in size, but a higher RDW suggests greater variation in sizes of the RBCs.
Normal Range
- 11.5-14.5%
Clinical Significance of Abnormal RDW
- This test can aid in differentiation of the causes of anemia.
- A normal RDW in the context of anemia, suggests it is due to chronic disease. For example, chronic kidney disease, diabetes, cancer or Crohn’s disease. Other causes include acute blood loss and aplastic anemia (failure of the bone marrow to produce enough RBCs).
- The most common cause of a high RDW is iron deficiency anemia. Causes for this, as discussed above include reduced dietary intake, malabsorption of iron and blood loss. Other causes for an elevated RDW are vitamin B12 or folate deficiency, hemolytic anemia, liver disease and chronic inflammatory conditions. Of note, a high RDW can also be a big indicator of oxidative stress in cancer patients. Oxidative stressis a state of imbalance between the production of harmful free radicals and the body’s ability to neutralize them with antioxidants.
The combination of low RBCs, hemoglobin, hematocrit and platelets is suggestive of bone marrow suppression and if you are getting treatments, you may need a break until these levels normalize. Blood transfusions are not ideal as they can increase oxidative stress by raising reactive oxygen species in the blood.
WHITE BLOOD CELL COUNT (WBC)
The white blood cell count measures the total number of white blood cells in a given volume of blood. WBCs are involved in the body’s defense mechanisms, fighting infections, detecting and destroying cancer cells and responding to inflammation. WBCs include neutrophils, lymphocytes, monocytes, eosinophils and basophils.
Normal Range
- 4,500-11,000 cells/µL
Clinical Significance of an Abnormal WBC Count
Leukopenia is a low WBC count (<4,000 cells/µL). Chronic illnesses like liver and kidney disease, bone marrow disorders, autoimmune diseases like lupus and rheumatoid arthritis, severe infections, chemo and radiation therapy and certain medications can all reduce WBCs. Deficiencies in vitamin B12, folate and copper can also impair WBC production. Leukemia is a well known cause of leukopenia. Leukopenia can significantly impair the immune system putting you at risk for serious infections.
Leukocytosis is a high WBC count. This is typically associated with infections (bacterial or viral), inflammatory conditions, leukemia or stress responses. Rising neutrophil levels can indicate a loss of immune function and cause a poor response to immune therapies and increased mortality.
WHITE BLOOD CELL DIFFERENTIAL COUNT
The differential count measures the relative proportions of different types of WBCs. This provides more detailed information about the cause of WBC abnormalities.
Normal Ranges
| WBC Type | Percentage | Absolute numbers |
| Neutrophils | 40-60% | 1,500-8,000 cells/uL |
| Lymphocytes | 20-40% | 1,000-4,800 cells/uL |
| Monocytes | 2-8% | 100-800 cells/uL |
| Eosinophils | 1-4% | 0-500 cells/uL |
| Basophils | 0.5-1.0% | 0-200 cells/uL |
Clinical Significance of Abnormal Differentials
- Neutrophilia (high neutrophils) is commonly seen with bacterial infections and inflammatory conditions.
- Neutropenia (low neutrophils) is the most common and clinically significant form of leukopenia, as neutrophils are the first line of defense against bacterial infections. Neutropenia significantly increases the risk of bacterial infections. Severe neutropenia (typically <500 cells/µL) is associated with a high risk of life-threatening infections, often requiring prompt intervention with broad-spectrum antibiotics. Neutropenia is commonly caused by cancer treatments.
- Lymphocytosis (elevated lymphocytes) is often seen with viral infections or chronic lymphocytic leukemia (CLL)
- Lymphopenia (low lymphocytes – T cells, B cells and natural killer cells) are critical for adaptive immunity, particularly in response to viral infections. Lymphopenia may increase susceptibility to viral infections such as influenza and COVID-19. It can also compromise the body’s ability to generate immune memory against infections. Lymphopenia can be caused by cancer treatments.
- Eosinophilia (high eosinophils) can indicate allergic reactions, parasitic infections or certain autoimmune conditions. If you are on mistletoe therapy and eosinophils rise above 5, you may need to stop treatment.
- Monocytosis (elevated monocytes) are often seen in chronic infections, especially viral and inflammatory disorders. This may indicate poor natural killer cell function.
- Monocytopenia (low monocytes): Monocytes are essential for both immune surveillance and phagocytosis (the ingestion of bacteria and cancer cells). Low monocytes indicate a non-functioning immune system. Although less common, monocytopenia can lead to impaired response to chronic infections and inflammation, as monocytes play a role in processing pathogens and promoting tissue repair.
- Basophilia (elevated basophils) are rare, but can occur in certain bone marrow disorders such as chronic myelogenous leukemia (CML).
High basophils, high monocytes and high eosinophils can be a signal of parasites and indicate gut dysbiosis and leaky gut.
PLATELET COUNT
The platelet count measures the number of platelets in a given volume of blood. Platelets, also called thrombocytes, are critical for blood clotting and wound healing. Platelets clump together to form blood clots and help stop bleeding after injury. They also release growth factors to aid in tissue repair.
Normal Range
- 150,000 – 450,000 cells/µL
Clinical Significance of Abnormal Platelet Count
- Thrombocytopenia (low platelets <150,000 cells/µL) is often caused by chemo and radiation therapy. Other causes include viral infections, toxins (pesticides and arsenic), autoimmune diseases, blood clotting disorders, leukemia and lymphoma. Certain anemias (aplastic, hemolytic), an enlarged spleen, severe systemic infections (sepsis), nutritional deficiencies (vitamin B12 and folate) and bone marrow failure as well as immune thrombocytopenia purpura also cause thrombocytopenia.
- Thrombocytosis (elevated platelets >450,000 cells/µL) may be a major early indicator of a cancering process. It is also associated with acute inflammatory responses, rapid blood loss, possibly a viral infection, iron deficiency anemia or certain types of cancer like leukemia and lymphoma. Having thrombocytosis can cause the blood to become thick and sticky increasing risks for clotting.
PLATELET VOLUME (MPV)
Platelet volume indicates the average size of platelets in the blood. Larger platelets are generally younger and more recently released from the bone marrow, while smaller platelets are older. Platelets play a crucial role in blood clotting.
Normal Range
- 7.5-11.5 fL
Clinical Significance of an Abnormal MPV
- High MPV may be seen in conditions like immune thrombocytopenia purpura (ITP). This is an autoimmune condition where the body mistakenly attacks its own platelets and destroys them. Certain proliferative bone marrow disorders or significant blood loss will cause elevated MPV.
- Low MPV can occur in conditions such as aplastic anemia or when the bone marrow is suppressed due to chemotherapy.
Of note, some studies suggest that high MPV may be associated with cardiovascular risk, as large platelets can be more reactive and prone to forming clots.
NEUTROPHIL TO LYMPHOCYTE RATIO (NLR)
As promised now I will tell you about a simple ratio you can calculate yourself and monitor from the numbers on your CBC. Simply take the neutrophil absolute number divided by the lymphocyte absolute number and this will give you the NLR.
It is surprising that doctors don’t check this anymore as the NLR is a known prognostic marker for various types of cancer, all cause mortality and response to standard of care treatments.
The ideal NLR is 2 or 2:1. Standard ranges may list 4:1 or 3:1, but 2:1 is optimum.
A high NLR (high neutrophils and low lymphocytes) reflects an imbalance in the immune system often indicating a state of systemic inflammation. It has been associated with poorer outcomes, including higher mortality rates and increased risk of cancer recurrence. It may also mean that treatment is overdone and you need a break if your other clinical symptoms are improving.
Patients with a high NLR may not respond as well to treatments. In this study they showed that an elevated NLR prior to immunotherapy was associated with a poorer response to treatment and a poorer prognosis. Read More
If the ratio is low because lymphocytes are higher than neutrophils, you have a “switched NLR”. This is often a sign of over treatment, blood dyscrasias (any disorder or abnormality of the blood) or blood cancers like leukemia or multiple myeloma.
Radiation can impact this ratio and it can take years to normalize.
It is best to monitor the trends of the NLR over time. Each time you get a CBC, calculate your ratio to see the trend. This can help you know if your treatments are working and see shifts in your immune status and overall health.
The neutrophil-to-lymphocyte ratio as a new prognostic factor in cancers: a narrative review Read More
IN CONCLUSION
I hope you found this review of the CBC helpful. Please refer back to this post when you get your next test results to help you understand what might be going on in your body. Proper interpretation of the CBC in conjunction with clinical findings and other diagnostic tests is essential, so discuss any concerns you have with your doctors. You have to be proactive when it comes to your health in today’s medical world!
May He give you the desire of your heart and make all your plans succeed. ~Psalm 20:4