CBC test for blood – clinical interpretation

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Whenever you get sick and visit the doctor. Most of the time, your doctor advised a CBC test for blood.

It is often recommended if you have a fever, weakness, fatigue, infection, inflammation, etc. 

CBC (or complete blood count test) is a medical laboratory test that analyzed the full blood count. It is one of the most routine laboratory tests. 

This test provides information on the quality, quantity, size, and shape of your blood count. This information also gives an idea to diagnose your disease. But it needs proper clinical correlation with your symptoms. 

Therefore, most doctors go for CBC tests in starting stage of almost all diseases. 

In this article, I will explain the crucial parameters of a CBC test for blood. But before that, we get brief information on blood and its composition. 


What is blood?

Blood is an essential biological fluid that constantly circulates in your body through blood vessels. It is a combination of blood cells (red blood cells, white blood cells, and platelets) and plasma. 

CBC test for blood

Normally, blood cells are suspended in plasma fluid. 

The primary function of blood to deliver oxygen/nutrients to tissues and remove carbon dioxide/waste products from your body.



What are the composition of blood and their percentage?

If you centrifuge your blood sample, you will see three layers in the test tube.

CBC test for blood These three layers represent – 

Top layer (yellowish color) – Plasma

Middle layer (yellowish-brown) – Buffy coat (White blood cells and platelets)

Lower layer (dark red) – Red blood cells (erythrocytes)

You can see a layer of dark red color at the bottom of the test tube. These are erythrocytes or red blood cells (RBCs). If we calculate the percentage (or volume) of erythrocytes in blood, it would call Packed cell volume (PCV). It is also known as hematocrit

Normally, it is present in 45%. Here, we can calculate PCV like – 

0.45 μL (microliter) = RBCs 

1 μL (microliter) = Blood

0.45/1×100 = 45%

Almost half portion of the blood contains RBC. The normal range of erythrocyte counts is around 5 million/μL or (50 lakh/microliter), which is vast in number.

You may see yellowish-brown color in the middle layer of a blood sample. These are buffy coats. It contains white blood cells (leukocytes) and platelets (thrombocytes). 

It is generally present in less than 1% of the whole blood. As far as the concern of blood cells count of buffy coat. It is normally present in a range of –

4800 to 11000 /μL = White blood cells 

1,50,000 – 4,50,000 / μL = Platelets

The remaining portion or upper portion of the blood sample is called plasma. It contains 55% of total blood. It is a slightly yellowish color.

The main components of plasma are water (90 -93%). Rest portion contains– 

1. Plasma protein 8%. There are three major types of protein in plasma – albumin (60%), globulins (alpha, beta, and gamma), and fibrinogen. 

2. Gases – oxygen (O2), carbon dioxide (CO2), and Nitric Oxide (NO).

3. Electrolytes – Na+, K+, Cl-

4. Nutrients – glucose, amino acids, fatty acids, vitamins, and minerals

5. Enzymes and hormones

6. Metabolic waste products like lactic acid, uric acid, creatinine, etc.



What are normal CBC levels?

The CBC is a blood test that evaluates your complete blood counts, including RBC (Red blood cells), WBC (White blood cells), and Platelets.

The range of CBC may vary from lab to lab. However, the normal range of full blood count as per modern hematology, 2nd edition by Reinhold munker  

CBC test for blood

What causes high red blood cell count, hemoglobin, and hematocrit?

Suppose, you have done a CBC test for blood and you find an elevated level of RBC count (erythrocytosis), hemoglobin, and hematocrit like – 

CBC test for blood


RBC = 7 million cells/ μL (4.5-6.5 million cells/ μL)

Hemoglobin = 18.5 g/dL (13.5-17.5 g/dL)

Hematocrit = 62% (40-52%)


These results may be due to –


1. Polycythaemia 

It usually happens if you live at a higher altitude (e.g., mountains area), then your body produces more RBC, hemoglobin content, and hematocrit volume to compensate for low oxygen level. 

2. Dehydration 

Your erythrocytes content becomes more concentrated during dehydration. It is mainly seen in excess sweating and less fluid intake. 

3. Lung and heart diseases (like ischemic heart disease

In this condition, your oxygen level starts to decrease. But our body has a dynamic feedback system. It helps to maintain oxygen levels. 

When you get hypoxia (less oxygen), then your body stimulates classical hormone erythropoietin (EPO) by the kidney. EPO sends a signal to stem cells of the bone marrow which helps in the production of RBCs. 

4. Cigarette smoking

It is a crucial factor that decreases your oxygen level and causes hypoxia. As a result, to make balance of oxygen level, your body increase RBC and hemoglobin content. 



What happens if RBC count is low? How do you read red cell indices?

If you find low hemoglobin, low hematocrit content, and less RBC count (erythropenia) in your blood report, that indicates anemia. Moreover, RBC indices (MCV, MCH, MCHC, RDW, and Retic. Count) clarify the diagnosis of your disease. 

RBC indices provide information on the shape, size, and physical characteristics of RBC. Normally, RBCs are biconcave disc-shaped. It becomes abnormal during anemia. 

You may feel weakness, tiredness,  shortness of breath, yellowish skin, and dizziness. Your doctor may correlate these results with your symptoms and other laboratory tests.

CBC test for blood

Note –

Low RDW – No clinical significance

High MCHC – rarely happen



What level of WBC is dangerous?

The leukocytes (WBC) have an important function in the fight against infection. It destroys the foreign organism through phagocytosis. 

The number of WBC is measure by the CBC test. It gives information on infection, allergic reaction, inflammation, blood cancer such as leukemia or lymphoma. 

The normal range of leukocyte count is 4,500 to 11,000 cells/ μL. It becomes dangerous if more than 11,000 cells/ μL indicates Leukocytosis and lower (<4,500 cells/ μL) than normal range called Leukopenia

It can be more dangerous or critical if it is less than 500 cells/μL that indicates the risk of fatal infection. If it is over than 30,000 cells/μL means massive illness or severe disease such as leukemia.


In Leukocytosis (High WBC count) – As per a study, Leukocytosis also impacts subtypes of WBC – neutrophils, lymphocytes, basophils, eosinophils, and monocytes.

1. Elevated neutrophils count (neutrophilia)– Your neutrophils count increases if you have a bacterial infection, chronic myeloid leukemia, chronic inflammation like rheumatic disease, pregnancy, trauma, smoking, stress, medications, and congenital disease.

2. Elevated lymphocytes count (lymphocytosis) – e.g., viral infection (like such as cytomegalovirus, Epstein-Barr), hepatitis, tuberculosis, hypersensitivity reactions, leukemia (cancer of blood cells), and lymphoma (cancer of lymphatic system).

3. Elevated eosinophils count (eosinophilia)– It is generally seen in allergic conditions, such as seasonal and environmental allergies. Some medications such as pain killers (NSAIDs), common antibiotics (nitrofurantoin, quinolones, cephalosporins, penicillins, sulfa-containing drugs) may cause eosinophilia. 

4. Elevated monocytes count (monocytosis) – It commonly happens if you have chronic infections, inflammation in the heart, cancer, and autoimmune diseases like rheumatoid disease.

5. Elevated basophils count (basophilia) – 

Like eosinophilia, it can be seen in allergic or anaphylactic conditions. Basophilia can also happen in inflammatory conditions, viral infections, endocrine diseases like diabetes and cancer. 


In Leukopenia (Low WBC count) – 

If you have a low WBC count, then you can’t fight against infection. Leukopenia is strongly associated with AIDS, HIV, dengue, malaria, aplastic anemia, and other immunocompromised diseases. 

It can also happen if you are taking medicines like – 

  • chemotherapy (almost all anticancer drugs)
  • prolonged use of steroid
  • antiepileptics medicines like lamotrigine
  • antipsychotic medicine – clozapine
  • antibiotics like Penicillin G, oxacillin, sulfasalazine, vancomycin, and trimethoprim-sulfamethoxazole
  • antimalarial – quinine
  • antirheumatic drugs like hydroxychloroquine, methotrexate.


If their subtypes count below the normal range, it would say – 

  • neutropenia (decrease neutrophils)
  • lymphocytopenia (decrease lymphocytes)
  • eosinopenia (decrease eosinophils)
  • monocytopenia (decrease monocytes) 
  • basopenia (decrease basophils)


Except for neutrophils, it does not much impact on other subtypes of leukocytes. Eosinopenia, monocytopenia, and basopenia are less frequently happen. 


When should I worry about my platelet count? Or What causes abnormal blood platelets?

The primary function of platelets to stop bleeding. If you get injury or inflammation, platelets help to make a clot to prevent bleeding. 

Although, platelets can slightly increase during inflammation. It can be a concern if there is damage to your blood vessels. In this circumstance, your body increases the platelets count from the normal range (>4,50,000) and deposits in the damaged area that makes a clot. 

The high platelet count is called thrombocytosis that can lead to a risk of clotting. It can also elevate in – 

  • Heart disease by atherosclerosis
  • Myeloproliferative disorders (bone marrow make too many blood cells)
  • Infection
  • Iron deficiency anemia and hemolytic anemia 
  • Inflammatory illness like rheumatoid arthritis, IBD (Inflammatory bowel disorder)
  • Cancer


If there is an unknown cause of high platelet count is called thrombocythemia

It may be life-threatening if your blood platelet count is below the normal range (<1,50,000), leading to the risk of bleeding. The lower platelet count is called thrombocytopenia

It is most commonly seen in dengue, malaria, typhoid, viral infection, vitamin B12 deficiency, leukemia, anemia, autoimmune disease, etc.

You may have decreased platelet count if you take medicine like valproic acid, methotrexate, isotretinoin, H2 blocker, and proton pump inhibitors. 




A CBC test does not reflect any particular disease. This is a helping tool to identify and diagnose the medical condition.

Your doctor may correlate the CBC report with your symptoms, medical history, current medication, and other factors. It can be used in regular health check-ups. 

I hope today’s post showed you how to read a CBC report. If you have any doubts regarding this post (CBC test for blood), please let me know by leaving a comment below.

If you found this article is informative, please share it on social media.


Sources –

1. Reinhold munker et al. Modern hematology. Biology and clinical management, 2nd edition. Humana press, new jersey, 2007. Chapter -1, 2, 5, and 7.

2. The Etiology and Management of Leukopenia

3. Drugs induced neutropenia 

4. Complete blood count

5. Megaloblastic Anemia and Other Causes of Macrocytosis

6. Complete blood count. Wikipedia


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One thought on “CBC test for blood – clinical interpretation
  1. Yogesh kumar

    Very nice

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