When we hear of iron in food or supplements we immediately think of the blood. Indeed the blood and specifically red blood cells require iron for its development and function. But iron is also needed by a host of other cells for different processes that sustain life. Iron is also needed for metabolic activities, for immune system functioning and for the production of a range of chemicals that are needed in the body. At times we do not give iron the same importance in human physiology as we do with other vitamins and minerals. But without iron, health and wellbeing would not be possible.
Iron In The Human Body
The human body sources all of its iron from food. Sometimes we do not get enough dietary iron due to our restrictions on the food we eat. At other times iron is lost during bleeding, or is not absorbed and assimilated properly. Whatever the case, the lower than normal levels of iron has various adverse effects on the body as does higher than normal levels. The signs and symptoms of these different conditions is one way of identifying the problem. But a blood test is the definitive measure of just how abnormally high or low the blood iron levels are at any point in time.
In order to understand what the iron blood test results mean, it is important to understand how iron is used in the body. For this purpose it is best to view iron in the body in terms of red blood cells – the carriers of gas through the bloodstream. Iron is part of hemoglobin – the compound in red blood cells that allows it to transport oxygen throughout the body. The total body iron is about 3.5 grams in men and 2.5 grams in women with about 60% of this iron being in hemoglobin and almost 30% stored as ferritin and hemosiderin.
Hemoglobin is made up of proteins and iron but it is the iron that plays the central role of binding to oxygen and carrying it in the bloodstream. Each hemoglobin molecule has four chains, each of which contain one iron atom. And each of these iron atoms bind to one oxygen molecule containing two oxygen atoms. In this way one iron atom can carry two oxygen atoms. So even though your body may have a normal number of red blood cells despite low iron levels, these red blood cells will not have the same oxygen-carrying capacity.
Human blood is made up of solids and liquids. The serum iron test measures the amount of iron in the liquid portion of blood. This does not include the iron in red blood cells that are circulating in the blood vessels. It is essentially a measure of the iron in transit which is being taken to the bone marrow to produce red blood cells. This level can vary during the course of the day and usually you will need to fast prior to the test. The serum iron is often done along with other iron tests.
- Low* = iron deficiency anemia, chronic illness
- Normal* = sideroblastic anemia
- High* = Hemochromatosis, hemolytic anemia, iron poisoning, sideroblastic anemia
* On its own the serum iron levels will not indicate these conditions unless considered in conjunction with the results of other iron tests.
Iron is transported through the blood by binding to a protein known as transferrin. It is the carrier protein to move iron through the bloodstream but should not be confused with hemoglobin, which is a protein containing iron that is found in red blood cells. Most of this iron is taken by transferrin to the bone marrow where it will be used to produce red blood cells. The remaining iron, if not utilized immediately, is stored in the tissues as ferritin and hemosiderin.
There are several tests that may be done to measure the transferrin levels. This includes total iron-binding capacity (TIBC) or unsaturated iron-binding capacity (UIBC). When considered with the results of a serum iron test, it will reveal the transferrin saturation levels which is a more useful indicator of the interplay between transferrin and iron in the blood. High levels usually occur when iron is low like in iron deficiency anemia. Low levels tend to occur when the iron levels are high or when the liver is not producing enough transferrin.
Ferritin is one form of iron storage. It is actually a protein which binds to iron and stores it within cells. Therefore ferritin levels reflect the body’s iron storage capacity. The major storage form is hemosiderin. Ferritin levels become low and depleted when there is insufficient iron to meet the body’s needs. It has to then turn to its stores. The levels of ferritin may be high when there is an overload of iron in the body, as the system takes the iron out of the bloodstream and stores it in the cells. Only small amounts of ferritin are normally found in the blood.
- Low* = Iron deficiency anemia
- Normal* = Iron poisoning, chronic illness
- High* = Chronic illness, hemochromatosis, hemolytic anemia, sideroblastic anemia
* Other blood iron test results need to be considered in conjunction with ferritin to be indicative of these conditions.
A hemoglobin test is often done as part of a complete blood count (CBC) or with other tests like the hematocrit. It is an iron test as such but if often done along with iron tests when conditions like iron deficiency anemia are suspected. Iron is one component of hemoglobin. High levels of hemoglobin is known as polycythemia and low levels is referred to as anemia. When it comes to iron specifically, low hemoglobin levels may be indicative of nutritional deficiencies in iron, loss of iron and blood from bleeding or increased utilization of iron during pregnancy.
The normal hemoglobin levels for adults are as follows:
- Men = 13.8 to 17.2 gm/dL (grams of hemoglobin per deciliter of blood)
- Women = 12.1 to 15.1 gm/dL
The results for children may vary according to age and gender. Newborns tend to have higher hemoglobin levels than older children and even adults but this is temporary.