RDW-SD (Red Cell Distribution Width) in fL

A high RDW means that the red blood cells vary a lot in size. There are many possible reasons why the RDW level can be too high. To determine what the possible cause of a high RDW level is, a comparison is made to the mean corpuscular volume (abbreviated MCV).

The MCV is the average amount of space occupied by each red blood cell.

If both the RDW and MCV levels are increased, there are several possible causes:

1. One possible cause is liver disease:

The liver is the largest organ in the body and is responsible for filtering (→ removing) harmful chemical substances, producing important chemicals for the body, and other important functions. Liver disease can increase RDW-SD due to several interconnected factors related to the liver's role in blood health and maintenance:

→ Hemoglobin Synthesis:

The liver plays a critical role in the synthesis of hemoglobin. Liver disease can impair this function, leading to imbalances in hemoglobin production and, consequently, red blood cell production.

→ Iron Metabolism:

The liver is central to iron metabolism, storing excess iron and releasing it as needed. Liver dysfunction can disrupt this balance, resulting in either iron deficiency or overload, which can both cause variations in red blood cell size and lead to a higher RDW-SD.

→ Erythropoietin Production:

While most erythropoietin (a hormone that regulates red blood cell production) is made in the kidneys, liver disease can indirectly affect its levels, impacting red blood cell maturation and leading to a greater variation in their sizes.

→ Dyserythropoiesis:

Liver diseases, particularly those causing cirrhosis (a condition in which your liver is scarred and permanently damaged), can lead to ineffective erythropoiesis, which is the production of red blood cells that are often of abnormal size or shape.

→  Nutrient Processing:

The liver processes many nutrients critical for red blood cell development, including vitamins B12, folate, and iron. Liver disease can lead to deficiencies in these nutrients, which are necessary for the proper production of red blood cells, thus resulting in a higher RDW-SD.

→ Inflammation:

Chronic liver disease is often associated with systemic inflammation, which can negatively affect red blood cell life span and production.

2. Another cause of high RDW & MCV levels is hemolytic anemia:

Hemolytic anemia can increase RDW-SD due to the premature destruction of red blood cells (RBCs) and the body's response to that destruction. Here's how it affects RDW-SD:

→ Premature RBC Destruction: Hemolytic anemia is characterized by the rapid destruction of red blood cells, which can occur in the bloodstream or in the spleen. This destruction shortens the lifespan of RBCs and leads to a decrease in their number.

→ Increased Reticulocyte Count: In response to anemia, the bone marrow increases production of new red blood cells, called reticulocytes, which are usually larger and less dense than mature red blood cells. This release of immature RBCs into the bloodstream increases the variability in cell size, thereby raising the RDW-SD.

→ RBC Size Variation: The presence of both smaller, potentially damaged red blood cells and larger, immature reticulocytes in circulation causes a wide variation in cell size, which is reflected by an increased RDW-SD value.

→ Response to Treatment: If the cause of hemolytic anemia is treated, such as stopping a medication that is causing the hemolysis (destruction of red blood cells) or treating an underlying infection, there may be a transient increase in RDW-SD as the bone marrow produces new RBCs to replace the ones that were destroyed.

→ Coexisting Deficiencies: Hemolytic anemia can be associated with nutrient deficiencies due to increased turnover of red blood cells. These deficiencies, particularly of vitamin B12, folate, or iron, can contribute further to the heterogeneity in red blood cell size.

→ Oxidative Stress: Conditions causing hemolytic anemia can also lead to oxidative stress, which can damage the red blood cell membrane and cause variation in red blood cell shapes and sizes.

Another scenario is that the RDW level can be high, but the MCV level can be low:

1. This can happen because of iron deficiency anemia.

Iron deficiency anemia is a decrease in hemoglobin in the blood that is caused by an inadequate supply of iron. Hemoglobin is a substance present in red blood cells that help carry oxygen to cells in the body. Iron is needed to make hemoglobin, which is why a decreased amount of iron leads to a decreased amount of hemoglobin.

2. Another cause of a high RDW level and a low MCV level is thalessemia intermedia.

Thalessemia intermedia is another type of blood disorder in which there is impaired production of one or more of the elements that make up hemoglobin. If the red blood cells are fragmented (broken) into smaller parts, this can cause the RDW to be high and the MCV to be low. In this situation, the red blood cells vary in size when they are broke up (which is why the RDW level is high) but the cells do not take up much space (which is why the MCV level is low).

A final possibility is that the RDW level is increased and the MCV level is normal.

This can be caused by the beginning stages of a decrease in vitamin B12 or folic acid in the body. It can also be caused by the beginning stages of iron deficiency anemia (see above).

What Does a Low RDW-SD Result Mean? Understanding Its Significance

Red Cell Distribution Width-SD (RDW-SD) is a laboratory parameter used in blood tests to measure the variation in size (or volume) of red blood cells (RBCs). It is part of a complete blood count (CBC) test and helps diagnose various conditions related to red blood cell abnormalities. Most often, RDW is used to detect the presence of anemia and other disorders that affect RBC size.

While high RDW-SD values are more commonly associated with medical conditions, low RDW-SD results can also hold clinical significance. This article will explore what a low RDW-SD result could indicate, potential symptoms, and possible treatment options.

What Does a Low RDW-SD Indicate?

RDW-SD measures the standard deviation in red blood cell size distribution. A low RDW-SD value implies that there is a smaller variation in the sizes of the red blood cells. In other words, the red blood cells are more uniform in size than usual. This could suggest a few different conditions:

1. Normal Healthy State
   In some cases, a low RDW-SD may not indicate any health problems. People with a healthy, balanced diet and normal red blood cell production may exhibit low RDW-SD levels. In such instances, it is considered normal, and no further investigation is typically needed.

2. Microcytic Anemia
   In some forms of anemia, such as microcytic anemia, red blood cells are uniformly small. Conditions like iron deficiency anemia or thalassemia (a genetic disorder affecting hemoglobin production) can result in uniformly smaller RBCs, leading to a lower RDW-SD value. However, in these cases, other blood parameters like mean corpuscular volume (MCV) would also be abnormal.

3. Bone Marrow Suppression or Dysfunction
   In rare cases, a low RDW-SD could point toward bone marrow suppression, where the bone marrow is not producing a diverse population of red blood cells. This could occur due to factors such as certain medications, chemotherapy, or chronic diseases that affect bone marrow function.

4. Chronic Illness or Inflammation
   In chronic illnesses or inflammatory conditions, the body may produce red blood cells with a uniform size due to a suppressed bone marrow response. This situation might not necessarily point to a specific disease but rather indicate a general systemic issue.

Symptoms Associated with Low RDW-SD

A low RDW-SD value on its own may not produce noticeable symptoms. However, if it is associated with an underlying condition, some symptoms may be present, depending on the specific issue:

- Fatigue: This could be a symptom if low RDW-SD is linked to anemia or iron deficiency.

- Pale or yellowish skin: Associated with certain types of anemia.

- Shortness of breath or dizziness: Could indicate anemia, especially if other blood parameters are abnormal.

- Weakness or lethargy: Especially if the bone marrow is not producing red blood cells effectively.

If you experience any of these symptoms, it’s essential to consult a healthcare professional to determine the underlying cause.

Diagnosing the Cause of Low RDW-SD

To understand what a low RDW-SD means in your specific case, doctors will often look at other parameters in the complete blood count (CBC), such as:

- Mean Corpuscular Volume (MCV): Measures the average size of red blood cells. If MCV is low, it may suggest microcytic anemia.

- Hemoglobin Levels: Low hemoglobin along with low RDW-SD may indicate anemia.

- Iron Studies: Tests such as serum ferritin or total iron-binding capacity (TIBC) can assess whether iron deficiency is a factor.

- Additional Tests: In some cases, more specialized tests may be needed to assess bone marrow function or check for inflammatory markers.

Treatment Options for Low RDW-SD

Treatment depends on the underlying cause of the low RDW-SD:

1. Iron Supplementation or Diet Changes
   If low RDW-SD is due to iron deficiency anemia, increasing iron intake through diet or supplements may help. Iron-rich foods include red meat, spinach, and lentils.

2. Treatment for Thalassemia
   Thalassemia management often involves blood transfusions, chelation therapy to remove excess iron, or medication to boost hemoglobin production.

3. Addressing Bone Marrow Issues
   If bone marrow suppression is the cause, treatment might involve stopping certain medications, using drugs to stimulate blood production, or, in severe cases, bone marrow transplantation.

4. Managing Chronic Illnesses or Inflammation
   If a chronic condition is the cause, managing the underlying disease, whether through medication, lifestyle changes, or other therapies, can improve red blood cell production and distribution.

When to See a Doctor

If a routine blood test shows a low RDW-SD, it doesn’t always mean something is wrong. However, if you experience symptoms such as fatigue, weakness, or shortness of breath, or have a family history of blood disorders, further medical evaluation is advisable.

Your doctor will likely conduct additional tests to pinpoint the cause and suggest appropriate treatment options. In some cases, simply monitoring the condition over time may be sufficient.

A low RDW-SD result indicates less variation in red blood cell sizes, which is generally less concerning than a high RDW-SD. However, it can still signal conditions like microcytic anemia, bone marrow suppression, or chronic illness. If you have symptoms that may suggest an underlying disorder, further testing and specific treatments may be needed.

Being proactive about your health by understanding your blood test results can help you and your healthcare provider make informed decisions. Regular check-ups and a balanced diet can also contribute to maintaining healthy red blood cell levels.