A decrease in the number of red blood cells or in the amount of hemoglobin (an oxygen-carrying protein) in these cells that may cause such symptoms as weakness, fatigue, dizziness, shortness of breath, headache, or insomnia. Anemia, in turn, may contribute to cardiovascular disease by forcing the heart to work harder to deliver sufficient oxygen to the brain and other organs.
There are several distinct types of anemia, which can be caused by vitamin or iron deficiencies, blood loss, a genetic abnormality in the shape of the cells, or some chronic diseases. Decreased production of red blood cells is a common complication of some kidney diseases, including diabetic nephropathy.
The red blood cells, which carry oxygen to tissues and organs throughout the body, are produced in the bone marrow. Healthy kidneys produce a hormone called erythropoietin (EPO), which stimulates the bone marrow to produce red blood cells when the blood oxygen concentration is low. However, diseased kidneys often don’t make enough EPO, causing a decline in red blood cell production.
Anemia may begin to develop in the early stages of kidney disease, when the individual still has 20% to 50% of his normal kidney function; it gets progressively worse as kidney function diminishes. Nearly everyone with end-stage kidney disease has anemia. In people receiving hemodialysis for kidney failure (a therapy in which the person’s blood is slowly pumped out of the body, through a special machine that filters out wastes and extra fluid, and back into the body), the treatment itself can sometimes contribute to the problem, through blood loss.
Doctors use a laboratory test called a complete blood count (CBC) to check for anemia. The CBC counts the number of red and white blood cells and the amount of hemoglobin (Hgb) in the blood, and it also determines the hematocrit (Hct), the percentage of whole blood that consists of red blood cells. When evaluating anemia, doctors will also test for iron deficiency and blood loss in the stool to rule out these potential causes of anemia.
In people with kidney disease, anemia can usually be treated with a genetically engineered form of EPO, which is usually injected under the skin two or three times a week. Often, they may need both EPO and iron supplements to raise their hematocrit level. Iron is sometimes given by pill, but intravenous iron supplementation appears to work better in people with kidney failure. Iron can also be injected directly into the tube that carries blood back to the body during hemodialysis.