Red Blood Cell Count: Understanding MCV, MCH, RDW, and More

Some of the most common blood tests are the red blood cell (RBC) indices. These are part of a larger battery of tests known as the complete blood count (CBC). The information offered by the RBC indices can provide valuable insights about your current health, possible diseases you may have, or how well you are responding to treatments.

As valuable as the tests are, understanding what a high RBC, low MCV, or low MCH mean can be difficult and confusing. But, with a little insight and education, you can make sense of the different tests and participate more actively in your healthcare decisions.

This article breaks down the various tests that make up the RBC indices, including what high and low test values mean.

What Is a Complete Blood Count?

The RBC indices are part of the larger complete blood count (CBC). The CBC is a battery of blood tests ordered by your healthcare provider to evaluate the composition and quality of the blood cells in your body.

The CBC not only includes white blood cells (leukocytes) that help fight infection and platelets (thrombocytes) that clot blood but also red blood cells (erythrocytes) that transport oxygen throughout the body

The complete blood count is so named because that is exactly what it does: count all the blood cells in a sample. The values are reported in different ways, sometimes by the actual number of cells in a sample of blood and, at other times, by the proportion of one group of cells to another group.

In their totality, these values can tell a healthcare provider a lot about the state of your health.

How to Read a Blood Test Report

The first step in learning how to read any blood test report is to understand the reference ranges of values. This is the set of values between which a blood test result is considered normal. It is validated through testing patients.

Simply put:

• Anything above the reference range of values is considered high (and is usually marked on the report as "High" or "H").
• Anything below the reference range of values is considered low (and is usually marked on the report as "Low" or "L").
• Anything between the high and low values is normal.

It's important to note that high and low values are "abnormal" but, on their own, don't necessarily mean anything until they are investigated further with other blood, lab, or imaging tests.

By way of example, hemoglobin values (used in part to detect anemia) are invariably higher at high altitudes than they are at sea level. Therefore, not only does the reference range for hemoglobin differ but so does the diagnostic definition of anemia.

Normal values can also sometimes differ by age, biological sex, and even race.

Red Blood Cell (RBC) Count

The red blood cell (RBC) count is the general starting point of any evaluation of red blood cells. As per its name, it simply counts the number of red blood cells in a sample of blood. The RBC count is measured in millions of cells per microliter (one-millionth of a liter), or cells/mcL.

A normal RBC count depends on age and sex:

• Women: 4.2–5.4 million cells/mcL
• Men: 4.7–6.1 million cells/mcL
• Children: 4.1–5.5 million cells/mcL

A low and high RBC count can mean any number of things, both benign and severe.

What Are Red Blood Cell (RBC) Indices?

Along with the RBC count, the RBC indices provide information about the quality of your red blood cells. The RBC indices look at specific components or characteristics of red blood cells, including their size and proportion.

The RBC indices also look at a protein in red blood cells called hemoglobin that is responsible for transporting oxygen from the lungs to the rest of the body. Hemoglobin is also the protein that gives red blood cells their red color.

The main components of the RBC indices include the mean corpuscular hemoglobin concentration (MCHC), the mean corpuscular volume (MCV), the mean corpuscular hemoglobin (MCH), and the red cell distribution width (RDW).

Mean Corpuscular Hemoglobin Concentration (MCHC)

The mean corpuscular hemoglobin concentration (MCHC) is the average concentration of hemoglobin in a sample of red blood cells. A corpuscle is simply a term used to describe a living cell, particularly red and white blood cells.

The MCHC basically tells whether you have more or less hemoglobin than what would be expected. The MCHC is measured in grams of hemoglobin per deciliter (one-thousandths of a liter) of blood, or g/dL.

A normal reference range for MCHC is between 32 and 36 g/dL in adults.

Low and high MCHC can mean any number of different things:

Mean Corpuscular Volume (MCV)

Mean corpuscular volume (MCV) measures the average volume of red blood cells. Any increase or decrease in the normal volume/size of a red blood cell can affect its ability to transport oxygen, leading to anemia. The MCV is measured in femtoliters (one thousand trillionths of a liter) per cell, or fL/cell.

A normal reference range for MCV is between 80 and 96 fL/cell.

Low and high MCV values can mean any number of things:

It's important to note that a person can have anemia and have a normal MCV. This is called normocytic anemia. Causes may include:

• Sudden blood loss
• Kidney failure
• Hemolytic anemia
• Nutritional deficiencies
• Anemia of chronic disease
• Rheumatoid arthritis
• Giant cell arteritis

Mean Corpuscular Hemoglobin (MCH)

Mean corpuscular hemoglobin (MCH) is the average amount of hemoglobin per red blood cell in a sample of blood. MCH is measured in picograms (one trillionth of a gram) per cell, or pg/cell.

The MCH value directly parallels the MCV value, and, for this reason, some healthcare providers find the test redundant. As such, if the size of the red blood cells is large (as measured by the MCV), the amount of hemoglobin per red blood cell will be high (as measured by the MCH), and vice versa.

A normal reference range for MCH is between 27 and 32 pg/cell.

The possible causes of low and high MCH tend to echo those of a low and high MCHC.

Red Cell Distribution Width (RDW)

Red cell distribution width (RDW) is a test that assesses the variability in the size of the red blood cells. A normal RDW would mean that your red blood cells are all similar in size, whereas a higher RDW means that there is more variability in the size of the red blood cells. This is called anisocytosis.

RDW values are described in percentages. It is instead calculated as the standard deviation of red blood cell volume/mean cell volume) × 100.

A normal reference range for RDW is 11.5% to 14.5%.

The interpretation of the RDW differs from the other blood tests in that it varies based on its relationship to the MCV. In short, the sizes and variability of red blood cells can indicate vastly different things.

Here are just a handful of examples:

Summary

Red blood cell (RBC) indices are a battery of tests that evaluate measurable characteristics of red blood cells, including their size and the concentration of hemoglobin in them. The tests include the mean corpuscular hemoglobin concentration (MCHC), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and red cell distribution width (RDW).

The test values can point a healthcare provider in the direction of the possible causes when compared to each other or to other blood, lab, or imaging test results.