CBC Test

A CBC test or Complete Blood Count test, is a blood test that helps determine your overall health status. This test can serve as a pointer to disorders ranging from different types of anaemia, infections, fever, inflammation and cancers.

The CBC test is usually prescribed as an essential blood test and can help guide further investigations. For example, it can be advised as a part of routine visits to your physician if your doctor suspects some illness or when you have symptoms such as bleeding, rashes, fever, discomfort or unexplained bruising.

The CBC test is also done at various stages of your treatment to monitor the progress of the patient and it is part of different health check plans offered at multiple hospitals.

The CBC test requires a sample of your blood for testing.

Anaemias, Infections, Bleeding disorders, Cancers, Inflammation, Fever, Bone marrow disorders

CBC test is helpful in monitoring, screening and diagnosis of various diseases. Some of them are-

• Infections
• Cancers
• Anaemia
• Bleeding disorders
• Vitamin and mineral deficiencies
• Autoimmune disorders
• Disorder of bone marrow
• Iron and vitamin B12 deficiency
• Allergies

This test helps point out various kinds of diseases and health conditions.

The CBC test results are usually used as a base parameter to aid in the diagnosis of a disease condition. Then, based on the CBC test reports, the doctor will advise additional investigations to confirm the diagnosis.

The main parameters that are checked for in the CBC test result are as follows -

The normal values and reference ranges of the test may vary from lab to lab. Please refer to the ranges mentioned in the report and consult a doctor to understand the interpretation of lab reports.

Each parameter is important in diagnosing different diseases in the individual.

Low RBC counts lead to anaemia. This may be due to -

• Acute or chronic bleeding
• RBC destruction - haemolytic anaemia
• Nutritional deficiency - iron deficiency, vitamin B12 or folate deficiency
• Bone marrow disorders or damage
• Chronic inflammatory disease
• Chronic kidney disease

The haemoglobin levels are usually low when the RBC count is low.

High RBC counts lead to polycythaemia. This may be due to -

• Dehydration
• Lung diseases
• Renal tumours or other tumours that produce an excess of erythropoietin
• Smoking
• Living at a high altitude
• Genetic causes (altered oxygen sensing, abnormality in haemoglobin oxygen release)
• Polycythemia vera - a rare disease

The haemoglobin levels are also usually high when the RBC count is high.

Low MCV and MCH values indicate red blood cells are smaller in size than normal. This could be due to -

• Iron deficiency anaemia
• Thalassaemia (little to no haemoglobin)

High MCV and MCH values indicate red blood cells are larger in size than normal. This could be due to -

• Vitamin B12 deficiency anaemia
• Folate deficiency anaemia
• Myelodysplasia (a condition where blood cells are formed poorly)
• Liver disease
• Hypothyroidism

Low MCHC values could be due to -

• Iron deficiency anaemia
• Thalassaemia

High MCHC values could be due to -

• Autoimmune haemolytic anaemia
• Hereditary spherocytosis (RBCs are destroyed earlier than normal)

Low reticulocyte count could be due to -

• Bone marrow disorder
• Nutritional deficiencies like iron deficiency, folate deficiency, B12 deficiency

High reticulocyte count could be due to -

• Bleeding disorders
• Haemolysis
• Response to treatment - iron supplementation for iron deficiency anaemia

Low WBC counts lead to leukopenia. This may be due to -

• Bone marrow disorders or damage
• Autoimmune conditions
• Severe infections (sepsis)
• Lymphoma or other cancer that spread to the bone marrow
• Dietary deficiencies
• Diseases affecting the immune system - HIV/AIDS

High WBC counts lead to leukocytosis. This may be due to -

• Viral or bacterial infections
• Inflammation
• Leukaemia, myeloproliferative neoplasms
• Allergies, asthma
• Tissue death caused due to trauma, burns, heart attack
• Intense exercise or severe stress

Low neutrophil count leads to neutropenia. This is due to -

• Severe, overwhelming infection (sepsis)
• Autoimmune disorders
• Dietary deficiencies
• Reaction to drugs
• Immunodeficiency
• Myelodysplasia
• Bone marrow damage (e.g., chemotherapy, radiation therapy)
• Cancers that spread to the bone marrow
• Congenital neutropenia

High neutrophil count leads to neutrophilia. This is due to -

• Acute bacterial infections
• Inflammation
• Trauma, heart attack, or burns
• Stress, rigorous exercise
• Certain leukaemias (e.g. chronic myeloid leukaemia)
• Cushing syndrome (production of excess cortisol)

Low lymphocyte count leads to lymphocytopenia. This is due to -

• Autoimmune disorders (e.g., lupus, rheumatoid arthritis)
• Infections (e.g., HIV, viral hepatitis, typhoid fever, influenza, Covid-19)
• Bone marrow damage (e.g., chemotherapy, radiation therapy)
• Corticosteroids

High lymphocyte count leads to lymphocytosis. This is due to -

• Acute viral infections (e.g., chickenpox, cytomegalovirus (CMV), Epstein-Barr virus (EBV), herpes, rubella)
• Certain bacterial infections [e.g., pertussis (whooping cough), tuberculosis (TB)]
• Toxoplasmosis (infection from a parasite)
• Chronic inflammatory disorder (e.g., ulcerative colitis)
• Lymphocytic leukaemia, lymphoma
• Stress (acute)

Repeated low monocyte count could be due to -

• Bone marrow damage or failure
• Hairy cell leukaemia
• Aplastic anaemia

High monocyte count could be due to -

• Chronic infections (e.g., tuberculosis, fungal infection)
• Infection within the heart (bacterial endocarditis)
• Collagen vascular diseases (e.g., lupus, scleroderma, rheumatoid arthritis, vasculitis)
• Monocytic or myelomonocytic leukaemia (acute or chronic)

High eosinophil count leads to eosinophilia. This is due to -

• Asthma, allergies such as hay fever
• Drug reactions
• Parasitic infections
• Inflammatory disorders (coeliac disease, inflammatory bowel disease)
• Some cancers, certain acute or chronic leukaemias or lymphomas
• Addison disease
• Connective tissue disorders

High basophil count could be due to -

• Rare allergic reactions (hives, food allergy)
• Inflammation (rheumatoid arthritis, ulcerative colitis)
• Certain leukaemias
• Uraemia

Eosinophil and basophil counts are normally low in healthy individuals. The differential WBC counts indicate a different medical condition, with each cell being high or low in the count. However, there are other specific investigations needed to confirm the diagnosis.

Low Platelet counts lead to thrombocytopenia. This can be due to -

• Viral infections like dengue, mononucleosis, measles, hepatitis
• Drugs like acetaminophen, quinidine, sulfa drugs
• Liver Cirrhosis
• Autoimmune disorders like Immune Thrombocytopenic Purpura (ITP),
• Sepsis
• Leukaemia, lymphoma
• Myelodysplasia
• Chemotherapy or radiation therapy
• Disorders of bone marrow or spleen

High Platelet counts lead to thrombocytosis. This is due to -

• Cancers like lung cancer, gut cancer, breast cancer, ovarian cancer, lymphoma
• Rheumatoid arthritis
• Inflammatory bowel disease
• Iron deficiency anaemia
• Haemolytic anaemia
• A myeloproliferative disorder like essential thrombocythemia

Your doctor cannot diagnose the above conditions based on a single CBC report. Instead, the doctor will advise a series of other investigations and clinical examinations and only confirm the diagnosis.