Anemia may also be related to the kidneys? There is a type of anemia called "renal anemia"!

Author: Zuo Li, Chief Physician, Peking University People's Hospital

Reviewer: Mao Yonghui, Chief Physician, Beijing Hospital

When talking about anemia, people often first think of factors such as iron deficiency and malnutrition. Nutritional anemia caused by these factors is caused by insufficient hematopoietic raw materials and is a common cause of anemia.

In fact, the causes of anemia are diverse. As a symptom, it can be caused by a variety of diseases, one of which is renal anemia.

1. What is renal anemia?

The kidneys can secrete a hormone called erythropoietin, which enters the blood circulation and reaches the bone marrow, promoting the production of red blood cells and releasing them into the blood. When kidney function is impaired, the secretion of erythropoietin decreases, leading to anemia, a condition called renal anemia.

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There is another mechanism for renal anemia: when kidney function is impaired, metabolic waste accumulates in the body, stimulating the immune system and leading to an inflammatory state, which can shorten the life of red blood cells. On the one hand, the number of newly generated red blood cells decreases; on the other hand, red blood cell destruction accelerates, eventually leading to anemia. In addition, in an inflammatory state, although the body has sufficient iron content, iron is stored in the body and cannot be used. Iron is one of the important raw materials for the production of red blood cells, further exacerbating the development of anemia.

Therefore, renal anemia is mainly the result of insufficient erythropoietin produced by the kidneys, combined with the inflammatory state that shortens the lifespan of red blood cells and the inability to utilize iron.

2. What tests are needed if anemia is suspected to be caused by kidney disease?

Renal anemia is a common complication of chronic kidney disease, characterized by impaired renal function, especially when the glomerular filtration rate is less than 30 ml/min or the serum creatinine concentration exceeds 300 μmol/L, the hemoglobin level decreases, resulting in normochromic normocytic anemia.

Chronic kidney disease is usually divided into five stages: stage 1, stage 2, stage 3a, stage 3b, stage 4 and stage 5. When it progresses to stage 3b, when kidney function has dropped to about half of normal, patients may begin to experience renal anemia. As kidney function further deteriorates, the degree of anemia will also increase.

The diagnosis of renal anemia is not based on specific markers, but is an exclusionary diagnosis. First, other possible causes of anemia, such as nutritional deficiency anemia or anemia caused by blood system diseases, need to be excluded. Only after these factors are excluded can the diagnosis of renal anemia be considered.

The diagnosis can be aided by assessing the correlation between renal function and the degree of anemia. For example, if anemia occurs in chronic kidney disease stage 3b, a hemoglobin level of approximately 10 g/dL would likely indicate that the anemia is caused by the kidney disease; however, if the hemoglobin level is as low as 6 g/dL, it would suggest that there may be other factors causing the anemia.

3. What should we pay attention to when treating renal anemia?

When kidney disease causes kidney function impairment, the accumulation of metabolic waste in the body will lead to increased toxin levels, which in turn stimulates the body to produce an inflammatory response. Therefore, when entering the dialysis stage, dialysis should be performed in a timely manner to remove toxins from the body.

Dietary control is essential for patients with kidney disease, but it must be moderate to avoid malnutrition due to excessive restrictions. The metabolic waste produced daily in the body needs to be excreted through the kidneys, so for patients with kidney disease, excessive intake will increase the burden on the kidneys and accelerate the progression of the disease. Therefore, it is necessary to maintain a balanced diet to ensure that the food consumed not only meets the body's needs but also does not put additional burden on the kidneys.

Iron is one of the key components for red blood cell production, but because inflammatory responses can lead to iron utilization disorders, it is necessary to supplement iron in appropriate amounts to ensure adequate iron reserves, while also avoiding excessive iron supplementation that may lead to iron overload.

In addition, exogenous erythropoietin supplementation is required to maintain hemoglobin levels within an appropriate range to support normal life. Excessive increases in hemoglobin levels require large amounts of erythropoietin supplementation, which may cause side effects. At the same time, rapid increases in hemoglobin levels should also be avoided.

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For the treatment of renal anemia, different patients have different responses to treatment. Whether it is through the injection of exogenous erythropoietin or the use of drugs to promote the production of endogenous erythropoietin, the efficacy needs to be evaluated two weeks after the start of treatment. This includes monitoring the hemoglobin level and adjusting the dosage according to its changes. If the hemoglobin level rises too quickly, the dosage needs to be reduced, and vice versa. The ultimate goal is to stabilize the hemoglobin level within an appropriate range and conduct regular reviews to ensure that the efficacy continues to be effective.