blood count

Blood Count 

Definition

One of the most commonly ordered clinical laboratory tests, a blood count, also called a complete blood count (CBC), is a basic evaluation of the cells (red blood cells, white blood cells, and platelets) suspended in the liquid part of the blood (plasma). It involves determining the numbers, concentrations, and conditions of the different types of blood cells.

Purpose

The CBC is a useful screening and diagnostic test that is often done as part of a routine physical examination. It can provide valuable information about the blood and blood-forming tissues (especially the bone marrow), as well as other body systems. Abnormal results can indicate the presence of a variety of conditions—including anemias, leukemias, and infections—sometimes before the patient experiences symptoms of the disease.

Description

A complete blood count is actually a series of tests in which the numbers of red blood cells, white blood cells, and platelets in a given volume of blood are counted. The CBC also measures the hemoglobin content and the packed cell volume (hematocrit) of the red blood cells, assesses the size and shape of the red blood cells, and determines the types and percentages of white blood cells. Components of the complete blood count (hemoglobin, hematocrit, white blood cells, platelets, etc.) can also be tested separately, and are sometimes done that way when a doctor wants to monitor a specific condition, such as the white cell count of a patient diagnosed with leukemia, or the hemoglobin of a patient who has recently received a blood transfusion. Because of its value, though, as an indicator of a person's overall health, the CBC package is most frequently ordered.

The blood count is performed relatively inexpensively and quickly. Most laboratories routinely use some type of automated equipment to dilute the blood, sample a measured volume of the diluted suspension, and count the cells in that volume. In addition to counting actual numbers of red cells, white cells, and platelets, the automated cell counters also measure the hemoglobin and calculate the hematocrit and the red blood cell indices (measures of the size and hemoglobin content of the red blood cells). Technologists then examine a stained blood smear under the microscope to identify any abnormalities in the appearance of the red blood cells and to report the types and percentages of white blood cells observed.

The red blood cell (RBC) count determines the total number of red cells (erythrocytes) in a sample of blood. The red cells, the most numerous of the cellular elements, carry oxygen from the lungs to the body's tissues. Hemoglobin (Hgb) is the protein-iron compound in the red blood cells that enables them to transport oxygen. Its concentration corresponds closely to the RBC count. Also closely tied to the RBC and hemoglobin values is the hematocrit (Hct), which measures the percentage of red blood cells in the total blood volume. The hematocrit (expressed as percentage points) is normally about three times the hemoglobin concentration (reported as grams per deciliter).

Red blood cell indices provide information about the size and hemoglobin content of the red cells. They are useful in differentiating types of anemias. The indices include four measurements that are calculated using the RBC count, hemoglobin, and hematocrit results. Mean corpuscular volume (MCV) is a measurement of the average size of the red blood cells and indicates whether that is small, large or normal. The red blood cell distribution width (RDW) is an indication of the variation in RBC size. Mean corpuscular hemoglobin (MCH) measures the average amount (weight) of hemoglobin within a red blood cell. A similar measurement, mean corpuscular hemoglobin concentration (MCHC), expresses the average concentration of hemoglobin in the red blood cells.

The white blood cell (WBC) count determines the total number of white cells (leukocytes) in the blood sample. Fewer in number than the red cells, WBCs are the body's primary means of fighting infection. There are five main types of white cells (neutrophils, lymphocytes, monocytes, eosinophils, and basophils), each of which plays a different role in responding to the presence of foreign organisms in the body. A differential white cell count is done by staining a smear of the patient's blood with a Wright's stain, allowing the different types of white cells to be clearly seen under the microscope. A technologist then counts a minimum of 100 WBCs and reports each type of white cell as a percentage of the total white blood cells counted.

The platelet count is an actual count of the number of platelets (thrombocytes) in a given volume of blood. Platelets, the smallest of the cellular elements of blood, are involved in blood clotting. Because platelets can clump together, the automated counting method is subject to a certain level of error and may not be accurate enough for low platelet counts. For this reason, very low platelet levels are often counted manually.

Normal results

Blood count values can vary by age and sex. The normal red blood cell count ranges from 4.2-5.4 million RBCs per microliter of blood for men and 3.6-5.0 million for women. Hemoglobin values range from 14-18 grams per deciliter of blood for men and 12-16 grams for women. The normal hematocrit is 42-54% for men and 36-48% for women. The normal number of white blood cells for both men and women is approximately 4,000-10,000 WBCs per microliter of blood.

Abnormal results

Abnormal blood count results are seen in a variety of conditions. One of the most common is anemias, which are characterized by low RBC counts, hemoglobins, and hematocrits. Infections and leukemias are associated with increased numbers of WBCs.

Resources

Books

Berkow, Robert, ed. Merck Manual of Medical Information. Whitehouse Station, NJ: Merck Research Laboratories, 1997.

Henry, J. B. Clinical Diagnosis and Management by Laboratory Methods. New York: W. B. Saunders Co., 1996.

---

count (kount) a numerical computation or indication.

---

Addis count  determining the number of erythrocytes, leukocytes, epithelial cells, casts, and protein content in an aliquot of a 12-hour urine specimen.

blood count , blood cell count determining the number of formed elements in a cubic millimeter of blood; it may be a complete blood count or it may measure just one of the formed elements.

complete blood count  a series of tests of the peripheral blood, including the hematocrit, the amount of hemoglobin, and counts of each type of formed element.

differential leukocyte count  a count on a stained blood smear of the proportion of different types of leukocytes (or other cells), expressed in percentages.

platelet count  determination of the total number of platelets per cubic millimeter of blood; the direct platelet c. simply counts the cells using a microscope, and the indirect platelet c. determines the ratio of platelets to erythrocytes on a peripheral blood smear and computes the number of platelets from the erythrocyte count.

---

blood count

n.

1. Calculation of the number of red blood cells, white blood cells, and platelets in a cubic millimeter of blood by counting the cells in an accurate volume of diluted blood.

2. The determination of the percentages of various types of white blood cells observed in a stained film of blood.

3. Complete blood count.

---

blood count.

See complete blood count.

---

blood count

the number of blood cells in a given sample of blood, usually expressed as the number of cells per liter of blood (RBCs × 10¹²/l, WBCs and platelets 10⁹/l). A differential white cell count determines the number of various types of leukocytes in a sampling of blood. The cell count is useful in the diagnosis of various blood dyscrasias, infections or other abnormal conditions of the body and is one of the most common tests done on the blood.

---

blood count

Complete blood count, see there

---

Patient discussion about blood count.

Q. what is a normal red blood cell count for breast cancer after operation

A. i know that the normal count is between 4.2 to 5.9 million cells/cmm. if you have anything else- i think this question should be to the Doctor...cause even if someone here will tell you it's ok that it's a bit low- the Doctor should know that and he has your chart with all your medical information. there for i would give him a phone call to ask if it's o.k. - unless you are in the normal average i told you, then you shouldn't worry about it.