Yes, managing kidney disease may help lower a high RDW in some cases, but it does not always do so. RDW measures how much red blood cells differ in size. Kidney disease can contribute to anemia, while low iron, vitamin B12 or folate, inflammation, and blood loss can also affect blood counts. Treating the cause—not the RDW number alone—is the key, with follow-up blood tests to see what changes.
What Does a High RDW Mean?
Red cell distribution width (RDW) is a measurement included in a complete blood count (CBC). It shows how much your red blood cells vary in size. When RDW is high, the cells are more different in size than expected. This finding can occur with anemia and several other medical conditions, including kidney disease. According to MedlinePlus, RDW is most useful when interpreted alongside other blood test results rather than as a stand-alone measure of health.
A high RDW does not automatically mean that kidney disease is worsening or that anemia is present. The result also cannot identify the exact cause of a blood abnormality. Hemoglobin, the average size of red blood cells, and other blood measurements help healthcare professionals determine whether further evaluation is needed. The laboratory's reference range should also be considered because normal ranges can vary.
How Can Kidney Disease Affect RDW?
Chronic kidney disease (CKD) can affect the body's ability to produce healthy red blood cells. Healthy kidneys make a hormone called erythropoietin, which signals the bone marrow to produce these cells. When kidney function declines, less of this hormone may be available, reducing red blood cell production. In people with CKD, red blood cells may also survive for a shorter time than usual. These changes can contribute to anemia and abnormal blood counts.
The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) explains that anemia associated with CKD can have several causes at once. Nutrient deficiencies, inflammation, infection, poor nutrition, and blood loss can contribute alongside reduced kidney function. These overlapping problems help explain why RDW may be high in someone with kidney disease and why treating the kidney condition alone may not resolve the blood test abnormality.
Other factors that may contribute to a high RDW
When investigating a high result, healthcare professionals may consider whether another condition is affecting red blood cell production or survival. Relevant possibilities include:
- Iron deficiency: The body may not have enough iron to make healthy red blood cells.
- Vitamin B12 or folate deficiency: These nutrients are needed for normal red blood cell production.
- Blood loss: Blood loss can contribute to anemia and may occur in people receiving dialysis.
- Inflammation or infection: These problems can affect red blood cell production and may coexist with kidney disease.
- Other medical conditions: Liver disease and certain blood disorders can also be associated with an elevated RDW.
These are possible contributors, not a checklist for identifying the cause of an individual result. More than one factor may be involved, so the evaluation depends on the person's blood counts, medical history, and other test findings.
Can Treating Kidney Disease Lower RDW?
Managing kidney disease may help address problems that contribute to abnormal blood counts, but a lower RDW is not guaranteed. Kidney care generally aims to slow further kidney damage, manage complications, and preserve health. The MedlinePlus guide to chronic kidney disease explains that treatment may include controlling blood pressure and blood sugar, taking prescribed medicines, and following an appropriate care plan.
If the elevated RDW is related partly to a treatable problem, such as iron deficiency or another nutritional deficiency, addressing that problem may improve blood cell production. However, if reduced erythropoietin production, ongoing inflammation, blood loss, or another condition continues to affect the blood, RDW may remain elevated even when kidney care is appropriate. The important goal is to identify and manage the underlying problems rather than trying to lower one laboratory number in isolation.
It is also important to distinguish between improving kidney health and treating anemia. Measures that slow CKD progression can protect kidney function, but they do not necessarily correct anemia that is already present. Anemia may require its own assessment and treatment, depending on the cause and the person's overall health.
How Is a High RDW Evaluated in Someone With Kidney Disease?
A healthcare professional usually reviews RDW as part of a CBC and compares it with other results. According to the Cleveland Clinic's explanation of RDW testing, clinicians may consider the average red blood cell size, also called mean corpuscular volume (MCV), and other blood measurements when investigating an abnormal result. This broader view helps distinguish between possible causes of changes in red blood cells.
Depending on the initial results and medical history, further tests may include:
- Hemoglobin and other CBC measurements: These help establish whether anemia is present and describe the pattern of the blood count.
- Iron studies: Ferritin and transferrin saturation can help assess iron stores and the amount of iron available to the body.
- Vitamin B12 and folate tests: These may be considered when a vitamin deficiency is possible.
- Kidney function tests: Blood and urine tests help assess kidney health and inform ongoing CKD management.
- Additional blood tests: Depending on the findings, a clinician may check reticulocyte counts or examine a blood smear to learn more about red blood cell production and appearance.
Not everyone needs every test. The choice depends on the person's symptoms, medical history, kidney function, other CBC findings, and whether the RDW has changed over time. Reviewing earlier blood test results can also help show whether the finding is persistent or new.
What Treatments May Help When RDW Is High?
Treatment is based on the identified cause, not simply on the RDW value. If CKD-related anemia is present, a clinician may consider treatments that support red blood cell production or correct a contributing deficiency. The National Kidney Foundation's guidance on anemia in CKD describes iron supplements, vitamin replacement when a deficiency is confirmed, and medicines that stimulate red blood cell production as possible options for selected patients.
Iron, vitamin B12, or folate should not be started automatically because RDW is high. These treatments are appropriate when the clinical assessment supports a deficiency or another specific reason for using them. People with CKD may also need individual dietary guidance because nutritional needs and restrictions can differ with kidney function and treatment status.
For some people, managing anemia requires more than one intervention. A healthcare professional may address a nutritional deficiency, investigate blood loss, review dialysis-related factors, or consider anemia medication when appropriate. Treatment choices depend on the person's hemoglobin level, other laboratory findings, symptoms, treatment history, and the possible benefits and risks of each option.
How Long Does It Take for RDW to Improve?
There is no single timeline for RDW to return to the reference range. Changes depend on the reason the result is high, how effectively that cause is addressed, and whether other factors continue to affect red blood cells. Even when anemia treatment improves hemoglobin or other blood measurements, RDW may not change at the same rate.
Follow-up blood tests help show whether treatment is improving the overall blood count. A clinician may compare RDW with hemoglobin, MCV, iron measurements, and kidney function over time. If RDW remains high, the next step may be to review the original explanation, consider other contributing causes, or decide whether further investigation is appropriate.
When Should You Discuss a High RDW With a Healthcare Professional?
If a blood test shows high RDW and you have kidney disease, discuss the finding with the healthcare professional managing your care. This is especially important if the result is new, remains elevated on repeat tests, or appears alongside a falling hemoglobin level or other abnormal blood counts.
Symptoms that may occur with anemia include:
- Unusual tiredness or weakness
- Shortness of breath during ordinary activities
- Dizziness or lightheadedness
- Pale skin or a racing heartbeat
- Difficulty concentrating
These symptoms can have causes other than anemia, but persistent or worsening symptoms deserve medical assessment. Seek immediate medical care for significant difficulty breathing or chest pain that does not go away. Do not change prescribed kidney medicines or begin supplements solely to lower RDW without discussing the result with your healthcare professional.
The Bottom Line
Managing kidney disease can help address some of the health problems associated with abnormal blood counts, and treating a related cause of high RDW may improve the result in some cases. However, kidney treatment does not reliably normalize RDW on its own. The most useful approach is to interpret RDW alongside the complete blood count, kidney function, iron and vitamin status when indicated, and the person's overall clinical picture. That information guides treatment and follow-up more effectively than the RDW number alone.