Anemia, a condition marked by a low count of healthy red blood cells, is common in dialysis patients. Red blood cells carry oxygen via hemoglobin. When their numbers are low, the body’s tissues and organs don’t get enough oxygen, causing fatigue and other symptoms. Dialysis filters waste and excess fluid from the blood, acting as an artificial kidney for those with kidney failure. Understanding why anemia is so prevalent in these patients is important.
Kidney Failure’s Impact on Erythropoietin
Healthy kidneys play a central role in red blood cell production by secreting erythropoietin (EPO). This hormone signals the bone marrow to produce and release new red blood cells. When blood oxygen levels decrease, kidney cells detect this and increase EPO production to stimulate more red blood cell formation.
In chronic kidney disease (CKD), damaged kidneys progressively lose their ability to produce sufficient EPO. As kidney function declines, EPO production falls significantly, leading to a marked reduction in the bone marrow’s ability to create red blood cells.
Inadequate EPO production means the body cannot naturally replenish its red blood cell supply. The severity of anemia in CKD patients often correlates directly with the degree of kidney function loss, as the bone marrow receives insufficient signals to maintain healthy red blood cell levels.
Iron Deficiency and Chronic Inflammation
Iron is a mineral essential for the production of hemoglobin, the oxygen-carrying protein within red blood cells. Without enough iron, the body cannot create sufficient hemoglobin, leading to iron-deficiency anemia. Dialysis patients often experience iron deficiency due to several contributing factors.
Dietary restrictions are common for dialysis patients, which can limit their intake of iron-rich foods. Additionally, the absorption of iron from food in the digestive tract can be impaired in these individuals. Even small, chronic blood losses, such as those occurring during dialysis treatments or from frequent blood tests, can deplete iron stores over time.
Chronic inflammation, highly prevalent in CKD and dialysis patients, further contributes to anemia. Inflammation triggers the release of proteins, including hepcidin, a hormone that regulates iron metabolism. Elevated hepcidin levels interfere with the body’s ability to utilize iron by blocking its absorption from the gut and preventing its release from storage. This inflammatory state can also directly suppress red blood cell production in the bone marrow and reduce the effectiveness of available EPO.
Blood Loss and Reduced Red Blood Cell Lifespan
The dialysis process itself can contribute to anemia through small but cumulative blood losses. During hemodialysis, blood passes through an artificial kidney, or dialyzer, and a small amount of blood may remain in the machine’s components after each treatment. Frequent blood draws for laboratory testing, necessary for monitoring a patient’s condition, also contribute to ongoing blood loss.
Furthermore, the uremic environment, characterized by the accumulation of toxins in the blood due to kidney failure, negatively impacts the lifespan of red blood cells. In healthy individuals, red blood cells typically circulate for about 120 days. However, in dialysis patients, this lifespan is significantly shortened, often to around 50 to 70 days.
This accelerated destruction means red blood cells break down more quickly than the body can replace them, even with some EPO production. The toxic substances present in the blood of kidney failure patients lead to increased oxidative stress and other changes that cause red blood cells to become more fragile and be removed from circulation prematurely.