Definition
A complete blood count (CBC) is a series of tests used to evaluate the composition and concentration of the cellular components of blood.
It measures the following:
- The number of red blood cells (RBCs)
- The number of white blood cells (WBCs)
- The total amount of hemoglobin in the blood
- The fraction of the blood composed of red blood cells (hematocrit)
- The mean corpuscular volume (MCV) — the size of the red blood cells
CBC also includes information about the red blood cells that is calculated from the other measurements:
- MCH (mean corpuscular hemoglobin)
- MCHC (mean corpuscular hemoglobin concentration)
The platelet count is also usually included in the CBC.
Purpose
The CBC provides valuable information about the blood and to some extent the bone marrow, which is the blood-forming tissue. The CBC is used for the following purposes:
- as a preoperative test to ensure both adequate oxygen carrying capacity and hemostasis
- to identify persons who may have an infection
- to diagnose anemia – those who suffer from anemia might take medication similar to methylfolate 15 mg to help with creating healthy red blood cells
- to identify acute and chronic illness, bleeding tendencies, and white blood cell disorders such as leukemia
- to monitor treatment for anemia and other blood diseases detected in human plasma and blood cells.
- to determine the effects of chemotherapy and radiation therapy on blood cell production
Preparation
There is no special preparation needed
How the Test is Performed
Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell with blood.
A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
In infants or young children, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any bleeding.
Tests
- White blood cell count (WBC): presence of infection
- Differential white blood cell count: specific patterns of WBC
- Red blood cell count (RBC): carries oxygen and carbon dioxide from lungs to tissue and vice versa
- Hematocrit (Hct): measures RBC mass
- Hemoglobin (Hgb): main component of RBC
- Red blood cell indices: calculated values of size and Hgb content of RBCs, important in anemia evaluation
- Platelet count: necessary for clotting and control of bleeding
- Red blood cell distribution width (RDW): indicates degree variability and abnormal cell size
- Mean platelet volume (MPV): index of platelet production
Normal Values
| TEST | NORMAL VALUES |
| Leukocyte (White Blood Cell) | X1000 cells/mm³ (µL) |
| Birth | 9.0-30.0 |
| 24 hours | 9.4-34.0 |
| 1 month | 5.0-19.5 |
| 1-3 years | 6.0-17.5 |
| 4-7 years | 5.5-15.5 |
| 8-13 years | 4.5-13.5 |
| Adult | 4.5-11.0 |
| Neutrophils Bands | 3-5% (total WBC count) |
| Segs | 54-62% |
| Lymphocytes | 25-33% |
| Monocytes | 3-7% |
| Eosinophils | 1-3% |
| Basophils | 0-0.75% |
| Erythrocytes (Red Blood Cells) | |
| Cord | 3.9-5.5 million/mm³ |
| 1-3 days | 4.0-6.6 million/mm³ |
| 1 week | 3.9-6.3 million/mm³ |
| 2 weeks | 3.6-6.2 million/mm³ |
| 1 month | 3.0-5.4 million/mm³ |
| 2 months | 2.7-4.9 million/mm³ |
| 3-6 months | 3.1-4.5 million/mm³ |
| 0.5-2 years | 3.7-5.3 million/mm³ |
| 2-6 years | 3.9-5.3 million/mm³ |
| 6-12 years | 4.0-5.2 million/mm³ |
| 12-18 years (male) | 4.5-5.3 million/mm³ |
| 12-18 years (female) | 4.1-5.1 million/mm³ |
| Hemoglobin | |
| 1-3 days | 14.5-22.5 g/dL |
| 2 months | 9.0-14.0 g/dL |
| 6-12 years | 11.5-15.5 g/dL |
| 12-18 years (male) | 13.0-16.0 g/dL |
| 12-18 (female) | 12.0-16.0g/dL |
| Hematocrit | |
| 1 day | 48-69% |
| 2 days | 48-75% |
| 3 days | 44-72% |
| 2 months | 28-42% |
| 6-12 years | 35-45% |
| 12-18 years (male) | 37-49% |
| 12-18 years (female) | 36-46% |
| Mean Corpuscular Volume (MCV) | |
| 1-3 days | 95-121µm³ |
| 0.5-2 years | 70-86 µm³ |
| 6-12 years | 77-95 µm³ |
| 12-18 years (male) | 78-98 µm³ |
| 12-18 years (female) | 78-102 µm³ |
| Mean Corpuscular Hemoglobin (MCH) | |
| Birth | 31-37 pg/cell |
| 1-3 days | 31-37 pg/cell |
| 1 week-1 month | 28-40 pg/cell |
| 2 months | 26-34 pg/cell |
| 3-6 months | 25-35 pg/cell |
| 0.5-2 years | 23-31 pg/cell |
| 2-6 years | 24-30 pg/cell |
| 6-12 years | 25-33 pg/cell |
| 12-18 years | 25-35 pg/cell |
| Mean Corpuscular Hemoglobin Concentration (MCHC) | |
| Birth | 30-36 g Hg/dL RBC |
| 1-3 days | 29-37 g Hg/dL RBC |
| 1-2 weeks | 28-38 g Hg/dL RBC |
| 1-2 months | 29-37 g Hg/dL RBC |
| 3 months-2 years | 30-36 g Hg/dL RBC |
| 2-18 years | 31-37 g Hg/dL RBC |
| Reticulocyte Count | |
| Infants | 2-5% of RBCs |
| Children | 0.5-4% of RBCs |
| 12-18 years (male) | 0.5-1% of RBCs |
| 12-18 years (female) | 0.5-2.5% of RBCs |
| Platelet Count | |
| Birth-1 week | 84,000-478,000/mm³ |
| Thereafter | 150,000-400,000/mm³ |
| ERYTHROCYTE SEDIMENTATION RATE (ESR) | |
| TEST | NORMAL VALUE |
| Westergren | |
| Child | 0-10 mm/hour |
| Adult (male) | 0-15 mm/hour |
| Adult (female) | 0-20 mm/hour |
| Wintrobe | |
| Child | 0-13 mm/hour |
| Adult (male) | 0-9 mm/hour |
| Adult (female) | 0-20 mm/hour |
What Abnormal Results Mean:
High numbers of RBCs may indicate:
- Low oxygen tension in the blood
- Congenital heart disease
- Cor pulmonale
- Pulmonary fibrosis
- Polycythemia vera
- Dehydration (such as from severe diarrhea)
- Renal (kidney) disease with high erythropoietin production
Low numbers of RBCs may indicate:
- Blood loss
- Anemia (various types)
- Hemorrhage
- Bone marrow failure (for example, from radiation, toxin, fibrosis, tumor)
- Erythropoietin deficiency (secondary to renal disease)
- Hemolysis (RBC destruction)
- Leukemia
- Multiple myeloma
- Malnutrition (nutritional deficiencies of iron, folate, vitamin B12, or vitamin B6)
Low numbers of WBCs (leukopenia) may indicate:
- Bone marrow failure (for example, due to infection, tumor or fibrosis)
- Presence of cytotoxic substance
- Autoimmune/collagen-vascular diseases (such as lupus erythematosus)
- Disease of the liver or spleen
- Radiation exposure
High numbers of WBCs (leukocytosis) may indicate:
- Infectious diseases
- Inflammatory disease (such as rheumatoid arthritis or allergy)
- Leukemia
- Severe emotional or physical stress
- Tissue damage (SUCH AS burns)
Low hematocrit may indicate:
- Anemia (various types)
- Blood loss (hemorrhage)
- Bone marrow failure (for example, due to radiation, toxin, fibrosis, tumor)
- Hemolysis (RBC destruction) related to transfusion reaction
- Leukemia
- Malnutrition or specific nutritional deficiency
- Multiple myeloma
- Rheumatoid arthritis
High hematocrit may indicate:
- Dehydration
- Burns
- Diarrhea
- Polycythemia vera
- Low oxygen tension (smoking, congenital heart disease, living at high altitudes)
Low hemoglobin values may indicate:
- Anemia (various types)
- Blood loss
The test may be performed under many different conditions and in the assessment of many different diseases.
Nursing Considerations
- Explain test procedure. Explain that slight discomfort may be felt when the skin is punctured.
- Encourage to avoid stress if possible because altered physiologic status influences and changes normal hematologic values.
- Explain that fasting is not necessary. However, fatty meals may alter some test results as a result of lipidemia.
- Apply manual pressure and dressings over puncture site on removal of dinner.
- Monitor the puncture site for oozing or hematoma formation.
- Instruct to resume normal activities and diet.
Resources:
US National Library of Medicine and the National Institute of Health – Medline Plus
Encyclopedia of Surgery
Lippincott’s Review Series Pediatrics Nursing
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