The blood is composed of cellular and liquid portions. Red blood cells, also known as erythrocytes, carry oxygen. A condition of lower red blood cell counts is called anemia, a condition that can cause weakness, fatigue and pale skin. Anemia is not a diagnosis by itself because it has an underlying cause. Causes of anemia include two classes. The blood cells can be low because of a problem with their production or their loss. A medical history, physical exam, and several lab tests can help discern what is causing the decreased production or increased loss.
Red Blood Cell Studies
Red blood cell studies characterize various aspects of the red blood cells. A red blood cell count measures the concentration of cells in the blood, similarly a hematocrit gives the percentage of blood that is made of red blood cells. Tests also measure the concentration of hemoglobin in the blood, a protein in red blood cells that carry oxygen. Similar tests discern the concentration of hemoglobin in the red blood cells, and the size or volume of the red blood cells. A reticulocyte count measures the number of new red blood cells in the blood, and studies of other cells, such as the white blood cell count or platelet count are also useful. For example, low levels of red blood cells, white blood cells and platelets suggests a possible bone marrow problem. Iron deficiency is more likely to create small red blood cells with decreased hemoglobin concentrations.
Iron Metabolism
A serum iron measures the concentration of iron in the blood. The ferritin level indicates how much iron is being stored, and the total iron binding capacity tells how much iron is being moved around the body by the protein transferrin. In iron deficiency anemia, the serum iron and ferritin are low, while the total iron binding capacity is high.
Blood Compounds
Other blood chemicals can be measured to rule out causes of anemia other than iron deficiency. Low vitamin B-12 and folate can cause anemia, and can be measure din the blood. If B-12 or folate levels are suspected are found to be low, methylmalonic acid and homocysteine can help make the diagnosis as well. Another cause for anemia is the destruction of red blood cells in the body, measures of the chemicals haptoglobin, bilirubin and LDH can help determine if this is a contributing factor.
Peripheral Smear
A peripheral smear is a study in which a small amount of blood is smeared across a glass slide, stained, and examined under a microscope. In iron deficiency anemia, the red blood cells will be variable in size, with many small cells, and a lighter color due to low amounts of hemoglobin.
Bone Marrow Biopsy
A more invasive but sometimes necessary and helpful test is the bone marrow biopsy. In this procedure, a small needle is inserted into the bone to extract bone marrow for tissue studies. The bone marrow is usually stained and observed under a microscope for any problems that could cause anemia.
References
- "Harrison's Principles of Internal Medicine"; Anthony S Fauci, et al.; 17th Ed 2008
- "Robbins and Cotran Pathologic Basis of Disease"; Vinay Kumar, et al.; 8th Ed 2009
- "Henry's Clinical Diagnosis and Management by Laboratory Methods"; Richard A. McPherson, et al.; 21st Ed 2006
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