WHAT SHOULD I DO IF MY RDW IS HIGH?

Finding an unfamiliar abbreviation flagged on your blood test results can feel unsettling, especially when you are not sure what it means or how concerned to be. If your RDW has come back higher than the reference range, the first thing to know is that a raised RDW is relatively common and does not automatically indicate something serious. What it does tell you is that your red blood cells are varying more in size than would normally be expected, and that is worth understanding and, in most cases, investigating a little further.

A full blood count includes RDW alongside other red blood cell markers and gives a much clearer overall picture. You can arrange one with no GP referral needed, and results are lab-reviewed and returned quickly.

RDW stands for red cell distribution width. It is a measurement included in a full blood count that reflects how much variation there is in the size of your red blood cells. In a healthy person, red blood cells are fairly uniform in size. When the body is struggling to produce red blood cells normally, whether due to a nutritional deficiency, an underlying condition or another cause, cells of different sizes start appearing in the bloodstream together. The RDW captures this variation.

The normal reference range for RDW is typically 11% to 14.5%, though this can vary slightly between laboratories. A result above this range suggests that there is greater size variation than expected, a state known medically as anisocytosis. The higher the RDW, the more pronounced the variation tends to be.

It is worth noting that RDW is always interpreted alongside other markers in the full blood count, particularly mean corpuscular volume (MCV), which measures the average size of red blood cells, and haemoglobin. Looking at these together gives a much more informative picture than RDW alone.

There are several common reasons why RDW can be elevated, and the most important step after receiving a high result is understanding which of these might apply to you.

Nutritional deficiencies are among the most frequent causes. Iron deficiency is particularly common and causes the body to produce smaller than normal red blood cells alongside normal ones, leading to variation in size. Deficiency in vitamin B12 or folate has a similar effect but in the opposite direction, producing larger than normal cells. Both of these are very treatable once identified.

Anaemia of various types can raise RDW, including iron deficiency anaemia, megaloblastic anaemia caused by B12 or folate deficiency, and anaemia related to thalassaemia, which is an inherited condition affecting haemoglobin production. In thalassaemia, the RDW pattern looks different and is usually interpreted alongside other characteristic findings.

Liver disease can also cause RDW to rise, as the liver plays a central role in regulating blood chemistry and supporting the production of healthy red blood cells. Chronic conditions including kidney disease, diabetes and certain inflammatory conditions have also been associated with changes in RDW.

A mildly raised RDW can sometimes follow a recent infection or a period of significant physical stress, and may return to normal without specific treatment once the trigger resolves. If you have recently had a blood transfusion, your RDW may temporarily appear elevated as your body contains two populations of red blood cells.

The appropriate next step depends on how high your RDW is, what the rest of your blood count shows, and whether you have any symptoms.

If your RDW is only mildly raised and all other markers in your full blood count are within normal range, and you have no symptoms, this may not require urgent action. It is still worth discussing with your GP, who can advise whether a repeat test or further investigation is appropriate.

If your RDW is raised alongside low haemoglobin, an abnormal MCV, or you have symptoms such as persistent fatigue, breathlessness, dizziness, pale skin or heart palpitations, this should be discussed with your GP promptly. These combinations can indicate anaemia that needs treatment, and identifying the underlying cause is essential because the treatment differs depending on the type.

If your result came from a private blood test, sharing it with your GP is a sensible step. They can assess it in the context of your wider health history and decide whether further investigation is needed, such as iron studies, B12 and folate levels, or other more specific tests.

There is no single treatment for a raised RDW because it is a finding rather than a diagnosis. What matters is addressing the underlying cause.

If iron deficiency is identified, treatment typically involves dietary changes to increase iron-rich foods such as red meat, dark leafy greens, pulses and fortified cereals, alongside iron supplementation in cases where deficiency is significant. Vitamin C alongside iron-rich foods can help with absorption.

If the cause is B12 or folate deficiency, supplementation is usually very effective and can lead to noticeable improvement in blood markers within a few weeks. B12 deficiency in particular can sometimes require injections rather than oral supplements, depending on the cause and severity.

Where the elevated RDW is linked to a more complex underlying condition such as liver disease, kidney disease or a chronic inflammatory condition, management focuses on treating that condition appropriately. This is why a proper clinical assessment matters rather than simply acting on the RDW number alone.

Supportive lifestyle measures such as regular moderate exercise, consistent sleep, a varied and nutritious diet, and reducing alcohol and tobacco can all support healthier blood cell production over time, though they are not a substitute for treating an identified cause.

Most cases of raised RDW do not require urgent attention, but there are situations where you should speak to a GP sooner rather than later. These include significant breathlessness or fatigue that is affecting your daily life, heart palpitations, chest pain, very pale or yellow skin, unexplained weight loss or persistent symptoms that you cannot explain.

If any of your results are significantly outside the reference range or your GP has previously flagged a concern, it is worth following up promptly rather than waiting.