Next, we move on to two other members of the anemia family—tests that begin to tell you if there is enough iron in your blood. If you read Module 6—Anemia and Kidney Disease, you already know the two tests that measure levels of iron in your blood are:
- Ferritin
- Transferrin saturation (TSAT)
If you didn't, don't worry, we'll explain them.
Iron is a key building block your body needs to make red blood cells. Hemoglobin contains iron. Your body absorbs some iron from foods you eat. But most of the iron used to make new red blood cells comes from old, broken-down red blood cells.
If you have anemia, you have fewer red blood cells—and fewer building blocks to make more.
Ferritin measures how much iron is stored in your body. Transferrin saturation (TSAT) measures how much of your stored iron can be used to make new red blood cells. What does this all mean?
When your ferritin or TSAT levels are too low, your doctor may prescribe iron supplements. Extra iron will help you to have enough building blocks to make new red blood cells.
Some anemia drugs work by telling your body to make more red blood cells. These drugs are called erythropoiesis stimulating agents, or ESAs. They include EPOGEN® (Epoetin alfa), Aranesp® (darbepoetin alfa), and PROCRIT® (Epoetin alfa). But they can't work properly if you don't have enough iron.
EPOGEN®? Aranesp®? PROCRIT®? What Do They Do?
One of the jobs of healthy kidneys is to make a hormone called erythropoietin (EPO). EPO signals your bone marrow to make red blood cells. When kidneys fail, EPO levels fall—and anemia is the result. Before 1989, people with kidney failure needed blood transfusions to temporarily give them enough red blood cells so they could function.
In 1989, EPOGEN®, the first synthetic erythropoiesis stimulating agent, or ESA, was made by Amgen Inc. (EPOGEN is also marketed as PROCRIT® by Ortho Biotech and is used by people with kidney disease who are not on dialysis). Now, instead of needing blood transfusions, people get weekly injections and grow their own red blood cells, just as they used to.
In 2001, Amgen introduced Aranesp®, which also tells the body to make more red blood cells. It lasts three times longer, so fewer injections are needed. Other drugs to stimulate red blood cell production are being tested.
Why Are Ferritin and TSAT Levels Different in Dialysis Patients?
Iron deficiency is very common in people on dialysis. In fact, as many as half of people on dialysis may not have enough iron to make healthy red blood cells! Ferritin and TSAT are the best two tests of how much iron is in the body.
Clinical practice guidelines for the care of people with kidney disease—the Kidney Disease Outcomes and Quality Initiative (KDOQI™) guidelines—say that people on dialysis should have a ferritin level of at least 100 ng/mL. The guideline for TSAT sets a level of greater than 20%.
Because people on dialysis have constant, small blood (iron) losses, there is very little chance that they could become overloaded with iron. For this reason, their levels of stored iron can safely be higher.
