1. Take the Blood Disorders Quiz

Medical Author:

Siamak T. Nabili, MD, MPH

Siamak T. Nabili, MD, MPH

Dr. Nabili received his undergraduate degree from the University of California, San Diego (UCSD), majoring in chemistry and biochemistry. He then completed his graduate degree at the University of California, Los Angeles (UCLA). His graduate training included a specialized fellowship in public health where his research focused on environmental health and health-care delivery and management.

View Full Profile

Medical Editor:

William C. Shiel Jr., MD, FACP, FACR

William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

View Full Profile

In this Article

• Anemia facts*
• What is anemia?
• What causes anemia?
• Can inadequate iron cause anemia?
• What about acute (sudden) blood loss as a cause of anemia?
• What are other causes of anemia?
• Can anemia be hereditary?
• What are the symptoms of anemia?
• How is anemia diagnosed?
• What is a complete blood cell (CBC) count?
• How is blood collected for a complete blood cell (CBC)?
• What is the red blood cell (RBC) count?
• What is hemoglobin?
• What does a low hemoglobin level mean?
• What is the hematocrit?
• How is hematocrit determined?
• How is anemia treated?
• What are the complications of anemia?
• What is the outlook (prognosis) for anemia?
• Blood and Bleeding Disorders FAQs
• Patient Comments: Anemia - Symptoms
• Patient Comments: Anemia - Levels
• Patient Comments: Anemia - Treatments
• Find a local Hematologist in your town
• Anemia Index

Blood is collected by venipuncture (using a needle to draw blood from a vein) in a lab, hospital, or physician's office. Typically, blood is collected in a special sterile tube from an arm vein. The tube has some preservatives to prevent clotting of the blood. Results may be available in an hour or longer depending on the setting.

In some instances, a quick in office test called hemoglobin rapid test may be performed using a few drops of blood from a finger prick. The advantage of this quick test is that results may be obtained in a few minutes and only a few drops of blood may be required.

The red blood cells (RBCs or erythrocytes) are the most common type of cells in the blood. We each have millions and millions of these little disc-shaped cells. The RBC count is done to determine if the number of red blood cells is low (anemia) or high (polycythemia).

In an RBC count, the number and size of the RBCs are determined. This is usually reported as number of RBCs per a specified volume, typically in millions of RBCs in microliters (one one-thousandth of an ml) of whole blood. The shape of the RBCs is also evaluated under a microscope. All of this information, the number, size and shape of the RBCs, is useful in the diagnosis of anemia. Further, the specific type of anemia may be determined by this information.

Hemoglobin is a red pigment that imparts the familiar red color to red blood cells and to blood. Functionally, hemoglobin is the key chemical compound that combines with oxygen from the lungs and carries the oxygen from the lungs to cells throughout the body. Oxygen is essential for all cells in the body to produce energy.

The blood also transports carbon dioxide, which is the waste product of this energy production process, back to the lungs from which it is exhaled into the air. The transport of the carbon dioxide back to the lung is also achieved by hemoglobin. The carbon dioxide bound to hemoglobin is unloaded in the lungs in exchange for oxygen to be transported to the tissues of the body.