CBC with differential
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Why the test is done?
The test may be done to assess your general health status. Your doctor may also order the test to evaluate you for certain conditions that affect your blood cells, such as anemia, inflammation, infection, cancer, or bleeding disorder.
When is it done?
This test is usually done in the following circumstances:
• As part of routine health checkup.
• When you have signs and symptoms of any condition that affects your blood cells.
• When you have a disease, to monitor its status and effectiveness of the treatment.
• When you are on a treatment that affects your blood cells such as chemotherapy.
What sample is needed and how is it collected?
The sample required is a blood sample, which is collected from the veins of your arm, typically from the site of your elbow fold.
What preparations are required before the test?
No specific preparation is required for this test.
What is tested?
The test evaluates your blood cells which consist of the Red blood cells (RBCs), White blood cells (WBCs), and the platelets. These cells perform many vital functions in your body such as supplying oxygen to the body cells, fighting infection, and others.
There are a number of conditions that affect these cells directly or indirectly. By checking these blood cells, your doctor can assess your general health status and evaluate you for conditions, such as anemia, infections, inflammations, and blood cancer.
This is done by means of a complete blood count (CBC) test, which consists of a number of tests that evaluate the various parameters of these blood cells.
Red Blood Cells
Red blood cells (RBCs), as the name indicates are the red-colored blood cells that give the blood its peculiar color. These are red due to the presence of a protein called hemoglobin which performs the vital function of carrying oxygen to all the parts of the body.
These cells are formed in the bone marrow and get released into the bloodstream where they have a life span of about 120 days. After that RBCs undergo breakdown and are replaced by new cells formed the bone marrow. Thus, to maintain the proper functioning of the RBCs, a constant supply of well-formed RBCs are needed.
There are multiple conditions that can affect the RBCs at different levels, causing its deficiency, leading to anemia:
• Production of RBCs: deficiency of iron, vitamin B12 and folic acid.
• Structure of the RBCs: sickle cell disease
• Loss of RBCs: due to bleeding.
White Blood Cells
White blood cells (WBC), also known as leukocytes, are another variety of the cells found in the blood. These cells are also found in the lymphatic system and tissues and forms a vital component of your body’s immune system. These cells help protect your body against infection and play a central role in inflammation and allergic reactions.
There are five types of WBCs, namely neutrophils, lymphocytes, monocytes, basophils, and eosinophils. The total number of WBCs and the proportion of each type remains relatively stable within a normal. However, certain conditions can lead to a decrease or increase in their number which can be detected by the blood test. These conditions can be:
• Bacterial infection: may cause an increase in total number of WBCs and/or increase in a number of neutrophils.
• Viral infection: may lead to increased lymphocytes.
• Allergies: may cause increased eosinophils.
• Blood cancers (leukemia): increased number of immature and mature WBCs.
Platelets
Platelets, also known as thrombocytes, are small cell fragments found in the blood. They play a central role in the clotting of the blood and prevent continued bleeding from the site of the injury.
They work by clumping together at the site of injury and by releasing chemicals that cause aggregation of more cells to form a clot.
There are a number of common and uncommon conditions that can affect the platelets and may cause a decrease or increase in its number:
Conditions causing a low platelet count:
• Viral infections such as dengue, mononucleosis, and other hepatitis, HIV, and others.
• Idiopathic thrombocytopenia (ITP)
• Use of certain drugs
Conditions causing a high platelet count (thrombocytosis):
• Anemia
• Inflammatory conditions
• Cancer
• Infection: such as tuberculosis
What tests are included in the CBC and differential?
A complete blood count is normally performed with an automated instrument that measures various parameters, including cell counts and physical structure. A typical CBC includes:
Red blood cell (RBC) tests:
• RBC blood cell (RBC) count is an estimate of the number of red blood cells present in the blood sample.
• Hemoglobin counts the amount of oxygen-carrying protein present in your blood.
• Hematocrit calculates the percentage of total blood volume that is constituted by the red blood cells.
• Red blood cell indices give information about the physical structure of the RBCs.
• Mean corpuscular volume (MCV) gives an estimate of the average size of your RBCs.
• Mean corpuscular hemoglobin (MCH) gives an estimate of the average amount of the hemoglobin present in your RBCs.
• Mean corpuscular hemoglobin concentration (MCHC) calculates the average concentration of the hemoglobin in your RBCs.
• Red cell distribution width (RDW) gives an estimate of the variation in the size of your RBCs.
Sometimes, the CBC may also consist of reticulocyte count, which is a dimension of exact count and percentage of new fresh red blood cells present in your blood sample.
White blood cell (WBC) tests:
• White blood cell (WBC) count gives the total number of WBCs found in your blood sample.
• White blood cells differential gives the number of five types of the WBCs separately, namely neutrophils, monocytes, lymphocytes, eosinophils, and basophils. This test can be done along with the CBC or once the CBC comes abnormal.
Platelet tests:
• Platelet count gives the total number of platelets found in your blood sample.
• Mean platelet volume (MPV) gives the measurement of average size of your platelets.
• Platelet distribution width (PDW) suggests the uniformity in the size of your platelets.
What does the test result mean?
If complete blood counts results come outside the established reference, then indicates the presence of diseases or conditions. Normally, other tests are also done to find out the exact cause of abnormal results. Sometimes, a blood smear is also examined through a microscope. The lab technician will assess the appearance and physical structure of blood cell such as size, shape, and color and will note down the abnormalities present in the blood cells. These test results give extra clues to the doctor regarding the cause of abnormal CBC results.
Doctor will evaluate and interpret the results in correlation with all the CBC test results. Depending on the purpose and findings of the test, doctor may ask for addition test for further investigations.
For additional details, see the table below:
| Test | Normal | Abnormal | Flag | Units | Reference range |
|---|---|---|---|---|---|
| Complete blood count | |||||
| White blood cells | 6.9 | K/mcL | 4.8-10.8 | ||
| Red blood cells | 1.8 | L | M/mcL | 4.7-6.1 | |
| Mean cell volume | 109.6 | H | fL | 80-100 | |
| Mean cell hemoglobin | 36.5 | H | pg | 27.0-32.0 | |
| Hemoglobin | 6.5 | L** | g/dL | 14.0-18.0 | |
| Hematocrit | 19.5 | L** | % | 42-52 | |
| Platelet count | 180 | K/mcL | 150-450 | ||
| Mean platelet volume | 7.9 | fL | 7.5-11.0 | ||
| Mean cell Hb concentration | 33.3 | g/dL | 32.0-36.0 | ||
| Red cell distribution width | 16.0 | H | % | 11.5-14.5 | |
| WBC Differential | |||||
| Neutrophil | 50 | % | 33-73 | ||
| Monocyte | 8 | % | 0-10 | ||
| Eosinophil | 5 | % | 0-5 | ||
| Lymphocyte | 36 | % | 13-52 | ||
| Basophil | 1 | % | 0-2 | ||
| Neutrophil, Absolute | 3.5 | K/mcL | 1.8-7.8 | ||
| Lymphocyte, Absolute | 2.5 | K/mcL | 1.0-4.8 | ||
| Eosinophil, Absolute | 0.4 | K/mcL | 0-0.45 | ||
| Basophil, Absolute | 0.1 | K/mcL | 0-0.2 | ||
| Monocyte, Absolute | 0.6 | K/mcL | 0-0.8 | ||
| Note: L= Abnormal low, L** = Critical value, H= Abnormal high, |
1. RBC count
| Test | Normal range | Low RBC count (anemia) causes | High count (polycythemia) causes |
|---|---|---|---|
| Red blood cells: Red blood cell count (RBC) | Men: 4.5-5.9x 106 /microliter Women: 4.1-5.1x 106 /microliter | Acute or chronic bleeding • Bone marrow disorders or damage • RBC destruction (e.g., hemolytic anemia, etc.) • Nutritional deficiencies like vitamin B12, iron deficiency and folate deficiency. | Acute or chronic bleeding • Excess production of the erythropoietin by the kidney or tumor • Dehydration • Genetic problems such as abnormal hemoglobin oxygen release and altered oxygen sensing • Lung (pulmonary disease) • Polycythemia vera- a rare disease |
Hb
| Low hemoglobin | High hemoglobin |
|---|---|
| Blood loss due to trauma and bleeding from colon cancer, ulcers and polyps etc | Lung disease- The body produces more red blood cells to compensate the low level of oxygen in the blood due to lung disease |
| Bone marrow damage due to chemotherapy, infection or toxin Bone marrow disorders like myelodysplastic syndrome and aplastic anemia and cancers like lymphoma, leukemia and myeloma etc. | Excessive production of the erythropoeitin caused by kidney tumors |
| Iron, vitamin B12 and folate deficiencies | Excessive production of red blood cells due to a rare disease called polycythemia vera |
| Kidney failure- Low production of hormone called erythropoietin due to severe and chronic kidney disease | Heavy smokers tends to have high level of hemoglobin. Some genetic causes such as abnormal release of the hemoglobin oxygen and altered oxygen sensing |
| Destruction of the red blood cells due to defects such as sickle cell anemia and hereditary spherocytosis etc | Congenital heart disease- Body produces more red blood cells to compensate the low level of the blood due to abnormality in the heart |
| Low production of the hemoglobin due to a disease called thalassemia | Dehydration causes the decreased level of fluid in the blood which body tries to compensate by artificially increasing the hemoglobin level |
2. WBC and differential
WBC count
| High WBC count (also known as leukocytosis) | Low WBC count (also known as leucopenia) |
|---|---|
| Normally caused by bacterial and viral infections | Damage to the bone marrow due to radiation therapy, chemotherapy and toxin etc Bone marrow disorders which causes insufficient production of the WBC |
| Leukemia myeloproliferative neoplasms | Autoimmune conditions such lupus in which body destroys it own WBC |
| Due to allergies and asthma | Diseases which affects the immune system of the body like HIV. It causes the destruction of the T lymphocytes |
| Inflammation and associated conditions like vasculitis, rheumatoid arthritis and inflammatory bowel disease. | Metastasized cancer and lymphoma |
| Conditions such as necrosis caused by burns, heart attack, trauma and surgery | Serious infections such as sepsis Vitamin B12 deficiency |
WBC Differential count
| Type of WBC | Causes of an increased count | Causes of a decreased count |
|---|---|---|
| Neutrophils (Polys, PMNs) | Known as neutrophilia • Acute bacterial infections and also some infections caused by viruses and fungi • Inflammation (e.g., inflammatory bowel disease, rheumatoid arthritis) • Necrosis (tissue death) caused by surgery, burns, trauma or heart attack • Physiological (stress, rigorous exercise) • Smoking • Pregnancy- last trimester or during labor • Chronic leukemia (e.g., myelogenous leukemia) | Known as neutropenia • Myelodysplastic syndrome. • Severe overwhelming infection (e.g., sepsis- neutrophils are used up) • Reaction to drugs (e.g., penicillin, ibuprofen, phenytoin, etc.) • Autoimmune disorder. • Chemotherapy • Cancer that spreads to the bone marrow • Aplastic anemia |
| Monocyte (Monos) | Known as monocytosis • Chronic infections (e.g., tuberculosis, fungal infection) • Infection within the heart (bacterial endocarditis) • Collagen vascular diseases like rheumatoid arthritis, lupus and scleroderma • Inflammatory bowel disease • Monocytic leukemia • Chronic myelomonocytic leukemia • Juvenile myelomonocytic leukemia | Known as monocytopenia Usually, one low count is not medically significant. Repeated low counts can indicate: • Bone marrow damage or failure • Hairy-cell leukemia |
| Lymphocytes (Lymphs, lym) | Known as lymphocytosis • Acute viral infections (e.g., hepatitis, chickenpox, cytomegalovirus (CMV), Epstein-Barr virus (EBW), herpes, rubella) • Infections caused by the bacteria such as tuberculosis and whooping cough • Lymphocytic leukemia • Lymphoma | Known as lymphopenia or lymphocytopenia • Autoimmune disorders (e.g., lupus, rheumatoid arthritis) • Infections (e.g., HIV, TB, hepatitis, influenza) • Bone marrow damage (e.g., chemotherapy, radiation therapy) • Immune deficiency |
| Basophils (Absolute basophil count, percent basophils) Baso, ABC, % baso | Known as basophilia • Rare allergic reactions (e.g., hives, food allergy) • Inflammation (rheumatoid arthritis, ulcerative colitis) • Some leukemias (e.g., chronic myeloid leukemia) | Known as basopenia Like eosinophils, numbers are usually low in the blood |
| Eosinophil (Eos, eos) | Known as eosinophilia • Asthma, allergies such as hay fever • Drug reactions • Inflammation of the skin (e.g., eczema, dermatitis) • Parasitic infections • Inflammatory disorders (e.g., celiac disease, inflammatory bowel disease) • Certain malignancies/ cancers. • Hypereosinophilic myeloid neoplasms | Known as eosinopenia It becomes difficult to determine because of the low numbers in the blood |
In certain cases, immature and/ or abnormal forms of the cells may be present in the blood and may be detected with a differential.
3. Platelet count
| Low platelet count | High platelet count |
|---|---|
| Antibody production against the platelets leads to idiopathic thrombocytopenia, also called as immune thrombocytopenic purpura | Lung cancer, ovarian cancer, breast cancer and other cancers can be the cause of high platelet count |
| Certain medications such as ibuprofen, aspirin, colchicine, H2- blocking agents, quinidine and hydralazine etc can also cause low platelet count | Use of oral contraceptives can also cause high platelet count |
| Heparin-induced thrombocytopenia can also lead to low platelets, when you develop an antibody with the treatment of heparin | Diseases like tuberculosis, inflammatory bowel disease and rheumatoid arthritis |
| Some viral infections such as hepatitis, measles, mononucleosis and HIV can also cause low platelet count | If your spleen is removed surgically |
| Recovery from surgery and trauma, alcohol consumption and vitamin B12 and folate deficiency | |
| Anemia, iron deficiency and hemolytic anemia can also cause high plate platelet count |
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