The Test Sample
What is being tested?
Iron is an essential nutrient to maintain life. It is needed in small quantities to help form normal red blood cells (RBCs) and is a critical part of hemoglobin, the protein in RBCs that binds oxygen in the lungs and releases it as blood circulates to other parts of the body.
Iron tests are ordered to evaluate the amount of iron in the body by measuring several substances in the blood. These tests are often ordered at the same time, where together, the results are considered in establishing the diagnosis and/or monitoring iron deficiency or iron overload.
- Serum iron measures the level of iron in the liquid portion of the blood.
- TIBC (total iron-binding capacity) measures all of the proteins in the blood that are available to bind with iron, including transferrin.
- UIBC (unsaturated iron-binding capacity) measures the portion of transferrin that has not yet been saturated. UIBC also reflects transferrin levels.
- Transferrin saturation is a calculation that reflects the percentage of transferrin that is saturated with iron.
- Serum ferritin reflects the amount of stored iron in the body.
Low iron levels can lead to anemia, causing decreased production of RBCs that are microcytic and hypochromic. Conversely, large quantities of iron can be toxic to the body. This occurs when too much iron is absorbed over time, leading to the accumulation of iron compounds in tissues, particularly the liver, heart, and pancreas.
Iron is normally absorbed from food and transported throughout the body by binding to transferrin, a protein produced by the liver. About 70% of the iron transported is incorporated into the production of red blood cell hemoglobin. The remainder is stored in the tissues as ferritin or hemosiderin, with additional small amounts used to produce other proteins such as myoglobin and some enzymes.
Iron deficiency may be seen with insufficient intake, inadequate absorption, or increased nutrient requirements as seen during pregnancy or with acute or chronic blood loss. Acute iron overload may often occur with excess ingestion of iron tablets, especially in children. Chronic iron overload may be due to excessive iron intake, hereditary hemochromatosis, multiple blood transfusions, and a few other conditions.
How is the sample collected for testing?
A blood sample is drawn by needle from a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
Fasting for 12 hours before sample collection may be required. In this case, only water is permitted.