Get In Touch With Us
MCH & RDW Blood Test: What High or Low Levels Mean
MCH and RDW help pinpoint the type of anaemia on your blood report. Here is what each measures, normal ranges, and what a high or low result means.
If your full blood count came back with "MCH" or "RDW" flagged high or low, you are not alone — these are two of the least-explained values on a blood report. Both describe your red blood cells in more detail than a simple count, and together they help pinpoint the type of anaemia, not just whether you have one. Here is what each measures and when to be concerned.
Key takeaways
- MCH (mean corpuscular haemoglobin) is the average amount of haemoglobin inside each red blood cell.
- RDW (red cell distribution width) measures how much your red blood cells vary in size.
- Neither value stands alone — they are read together with your full blood count to narrow down the cause of anaemia.
- A single abnormal MCH or RDW is common and often mild; persistent or combined abnormalities are what prompt further testing.
What is MCH in a blood test?
MCH stands for mean corpuscular haemoglobin — the average amount of haemoglobin (the oxygen-carrying protein) inside each of your red blood cells. It is calculated automatically as part of a full blood count (FBC/CBC), alongside related values like MCV (red cell size) and MCHC (haemoglobin concentration).
A typical adult MCH range is approximately 27–33 picograms (pg) per red blood cell, though this varies slightly by laboratory.
What does a high MCH level mean?
A high MCH means your red blood cells are carrying more haemoglobin than average per cell. Common causes include:
- Macrocytic anaemia — often linked to vitamin B12 or folate deficiency, where red blood cells are abnormally large and carry more haemoglobin each.
- Liver disease or excessive alcohol use, which can enlarge red blood cells.
- Thyroid conditions , in some cases.
What does a low MCH level mean?
A low MCH means each red blood cell is carrying less haemoglobin than average. The most common cause is:
- Iron deficiency anaemia — without enough iron, your body cannot make enough haemoglobin, so each cell carries less of it.
- Thalassaemia — an inherited blood condition, which is one reason doctors look at MCH and MCV together.
- Chronic blood loss , including from heavy periods.
What is RDW in a blood test?
RDW stands for red cell distribution width — it measures how much variation there is in the size of your red blood cells, not their number or haemoglobin content. Healthy red blood cells are usually fairly uniform in size; a high RDW means your red cells vary more than usual — some abnormally small, some abnormally large, or both.
A typical adult RDW range is approximately 11.5–14.5% .
Why RDW matters: on its own, RDW rarely tells you much. But combined with MCV and MCH, it helps distinguish between different causes of anaemia — for example, iron deficiency typically raises RDW, while some inherited conditions do not.
MCH and RDW together: reading the pattern
| Pattern | Possible meaning |
|---|---|
| Low MCH + high RDW | Classic pattern for iron deficiency anaemia |
| Low MCH + normal RDW | May suggest thalassaemia trait rather than iron deficiency |
| High MCH + high RDW | Often seen in vitamin B12 or folate deficiency |
| Normal MCH + normal RDW | Red cells are typically uniform and normally sized |
This is exactly why a full blood count is read as a set of values rather than one number at a time — MCH and RDW only become meaningful alongside haemoglobin, MCV and your symptoms.
When should you worry about MCH or RDW levels?
A single, mildly abnormal MCH or RDW result — especially with no symptoms — is common and often not a cause for alarm. It is worth discussing with a doctor or dietitian when:
- The result is significantly outside the normal range.
- You also have symptoms such as fatigue, pale skin, dizziness or shortness of breath.
- The abnormality persists across repeat tests.
- It appears alongside other abnormal values, such as low haemoglobin.
What to do if your MCH is low
If a low MCH points toward iron deficiency, the usual next steps are an iron studies test (ferritin, serum iron, transferrin saturation) to confirm the cause, followed by dietary changes or supplementation as advised. This is exactly where a dietitian-led review helps — turning "your MCH is low" into a specific, practical eating plan rather than a number to worry about.
Why read your full blood count with a dietitian
MCH and RDW are two of the most commonly misunderstood values on an FBC report — easy to flag, hard to interpret alone. At HDC Medical, your full blood count is reviewed one-to-one, so an abnormal MCH or RDW comes with a clear explanation and next step, as part of our full body health screening .
Reviewed by Jaceme Chuah
Registered Dietitian (MDA) · IDF Diabetes Educator · HRD Corp Accredited Trainer
Jaceme leads HDC Medical’s one-to-one blood report reviews, with 8+ years of clinical nutrition experience and 2,000+ consultations. View her full profile →
This article is for general education and does not replace personalised medical advice. Reference ranges vary between laboratories — always interpret your results with a qualified professional. Blood screening is a monitoring and early-flag tool, not a diagnosis. HDC Medical is a dietitian-led health screening centre in Mutiara Damansara, Petaling Jaya.
Frequently asked questions
When should I worry about MCH levels?
A single mildly abnormal MCH with no symptoms is usually not urgent. Worth discussing with a doctor if the result is significantly outside range, persists on repeat testing, or comes with symptoms like fatigue or pale skin.
What does it mean when my MCH is low?
A low MCH usually means your red blood cells are carrying less haemoglobin than average, most commonly due to iron deficiency. It is often reviewed alongside MCV and RDW to narrow down the cause.
What does it mean when my MCH is high?
A high MCH usually means your red blood cells are carrying more haemoglobin than average, often linked to vitamin B12 or folate deficiency, or liver-related causes.
What is a normal RDW range?
A typical adult RDW range is around 11.5–14.5%, though this varies by laboratory. RDW is most useful when interpreted together with MCV and MCH.
What should I do if my MCH is low?
Your doctor may order further tests such as iron studies to confirm the cause. A dietitian review can then turn the result into a specific, practical dietary plan.
Get your full blood count explained, not just flagged.
MCH, RDW and every other value on your report reviewed one-to-one at HDC Medical, Petaling Jaya.
WhatsApp Us — Book a Screening
or read our
FBC blood test guide
