High MCH on Your Blood Test Explained
What elevated mean corpuscular haemoglobin means, how it differs from MCV and MCHC, the most common causes, and the workup your GP will follow — in plain English.
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The Quick Answer
MCH stands for mean corpuscular haemoglobin — the average mass of haemoglobin packed into a single red blood cell. The Australian normal range is roughly 27-33 picograms (pg). When MCH is above 33-34 pg, it is called hyperchromia.
High MCH almost never occurs in isolation. Because bigger red cells naturally contain more haemoglobin, MCH almost always rises alongside a high MCV (mean corpuscular volume). This means the causes are essentially identical to high MCV: vitamin B12 deficiency, folate deficiency, regular alcohol use, and hypothyroidism are the big four. Uploading your full blood count PDF to SmarterBlood will show you MCV, MCH, MCHC, and all related markers side by side, explained in plain English with AU reference ranges.
What MCH Actually Measures
Your full blood count (FBC) is performed by an automated analyser that measures millions of individual red cells. For each cell it measures the volume directly and calculates how much haemoglobin it contains by measuring the amount of light the cell absorbs. MCH is then simply the total haemoglobin divided by the total red cell count — an average mass per cell.
Because MCH = total haemoglobin ÷ red cell count, the only ways to get a high MCH are: cells that are genuinely larger than normal (the most common explanation), a falsely high haemoglobin reading from a lab artefact (lipaemia, cold agglutinins), or a very high percentage of large reticulocytes. The first scenario — large cells — is why MCH and MCV almost always move together.
MCH vs MCV vs MCHC — What Is the Difference?
These three red cell indices are reported together on every full blood count and are frequently confused. The table below clarifies what each one measures.
Average SIZE of a red blood cell
Macrocytosis - B12, folate, alcohol, hypothyroidism, liver disease
Microcytosis - iron deficiency, thalassaemia, anaemia of chronic disease
Average AMOUNT of haemoglobin per red cell
Hyperchromia - almost always tracks with high MCV; same causes
Hypochromia - iron deficiency, thalassaemia; tracks with low MCV
CONCENTRATION of haemoglobin inside each cell
Rare; usually a lab artefact (lipaemia, cold agglutinins, spherocytosis)
Iron deficiency, thalassaemia - pale, hypochromic cells
Key takeaway: A high MCHC is almost always a lab artefact — cells cannot actually be hyperconcentrated with haemoglobin beyond about 360-370 g/L without rupturing. If your MCHC is flagged high, the result is almost certainly being driven by lipaemia, cold agglutinins, or spherocytosis (in hereditary spherocytosis, the cells are small and dense).
Causes of High MCH
Causes are grouped as megaloblastic (DNA-synthesis problems), non-megaloblastic (other mechanisms), and artefactual (lab or sample issues). The distinction affects how urgently the cause needs to be treated.
Vitamin B12 deficiency
Pernicious anaemia, vegan or vegetarian diet, gastric surgery, long-term metformin or proton pump inhibitor use. B12 is essential for DNA synthesis; deficiency causes impaired red cell division and larger, haemoglobin-rich cells. Can cause permanent nerve damage if untreated.
Folate deficiency
Poor diet (low leafy greens), alcohol, pregnancy (increased demand), coeliac disease, methotrexate, phenytoin, and sulfasalazine. Always check B12 before treating with folic acid - folate replacement in B12 deficiency can mask the anaemia while neurological damage progresses.
Alcohol (regular use)
Direct bone marrow toxicity and impaired folate metabolism both raise MCV and MCH in parallel. Often the first objective laboratory sign of heavy drinking. Returns to normal within 2-4 months of abstinence.
Hypothyroidism (underactive thyroid)
Slowed red cell production and metabolism raises both MCV and MCH. TSH should always be checked in unexplained macrocytosis. Coexists with B12 deficiency more often than chance because both can have an autoimmune basis (Hashimoto thyroiditis and pernicious anaemia both involve autoimmunity).
Liver disease
Cirrhosis, fatty liver, and hepatitis alter red cell membrane lipid composition, increasing cell size and consequently MCH. Often overlaps with alcohol use as a cause.
Reticulocytosis
After acute blood loss or haemolysis, the bone marrow releases young red cells (reticulocytes) that are larger than mature cells and contain more haemoglobin. This is transient and resolves as the bone marrow catches up.
Medications
Methotrexate, hydroxyurea, zidovudine, phenytoin, valproate, sulfasalazine, trimethoprim, and capecitabine all interfere with DNA synthesis or folate metabolism and can raise MCH as well as MCV.
Lipaemia (very high triglycerides)
Very high levels of lipids in the blood sample interfere with the spectrophotometric measurement of haemoglobin, causing a falsely high MCH reading. If MCH is unexpectedly high, a non-fasting or post-meal sample taken from someone with severe hypertriglyceridaemia may be the cause.
Cold agglutinins
Cold agglutinins are antibodies that cause red cells to clump at low temperatures, falsely lowering the red cell count and raising calculated MCH. More common in older adults and after certain infections (Mycoplasma pneumoniae, EBV). A sample analysed at 37 degrees resolves the artefact.
When Does a High MCH Actually Matter?
MCH elevation matters primarily as a signpost to an underlying cause — it is not harmful in itself. The clinical significance depends almost entirely on what is causing it:
Mildly high MCH, no symptoms, recent alcohol use or medication change
Retest after addressing the likely cause. No urgent action needed.
MCH above 36 pg with fatigue and pale skin
Macrocytic anaemia from B12 or folate deficiency. GP appointment within 1-2 weeks.
MCH above 38 pg with tingling or numbness
Possible severe B12 deficiency with neurological involvement. See GP within days.
High MCH plus low WBC or low platelets
Pancytopenia with macrocytosis - severe deficiency or bone marrow disorder. GP urgently.
Unexpectedly isolated high MCH with normal MCV
Request repeat test on fresh sample. Check for lipaemia or cold agglutinins.
Persistent high MCH despite B12 and folate treatment
Other cause not yet identified. Haematology referral warranted especially if over 60.
Red Flags — When to See Your GP Promptly
MCH above 38-40 pg with neurological symptoms
Tingling, numbness, balance problems, or memory changes alongside very elevated MCH strongly suggest severe B12 deficiency with nerve involvement. This needs urgent investigation and treatment to prevent permanent damage.
High MCH plus low haemoglobin (macrocytic anaemia)
The combination means the deficiency is advanced enough to impair red cell production. Fatigue and shortness of breath will be prominent and treatment is more urgent.
High MCH plus low white cells or low platelets
Involvement of all three blood cell lines (pancytopenia) alongside macrocytosis suggests severe B12 deficiency or a bone marrow disorder. Needs prompt haematology review.
Persistent elevation after B12 and folate treated
If MCH remains high after 3 months of B12 or folate replacement and confirmed compliance, there may be a second cause. Revisit medications, alcohol, thyroid function, and consider haematology referral.
What Your GP Will Do Next — The Workup
Because MCH and MCV almost always rise together, the investigation follows the same pathway as for macrocytosis. The sequence below is standard for Australian GPs.
Check vitamin B12 and red cell folate
These two tests are the first and most important investigation for elevated MCH with a raised MCV. Serum B12 below 150 pmol/L is definitively low; 150-220 pmol/L is borderline and may need active B12 (holotranscobalamin) or methylmalonic acid to confirm. Red cell folate is a better indicator of tissue folate stores than serum folate.
Thyroid function test (TSH)
A simple, cheap, bulk-billable test. Hypothyroidism is a common, reversible cause of macrocytosis and a major risk factor for B12 deficiency (both can be autoimmune). An abnormal TSH may immediately explain the MCH elevation.
Liver function tests and GGT
Liver disease and alcohol both raise MCH. GGT is the most sensitive single marker of recent alcohol use and hepatic inflammation. ALT, AST, ALP, and bilirubin screen for hepatitis, fatty liver, and cirrhosis.
Review medications and alcohol history
A careful history is often the most efficient diagnostic tool. Many people are unaware that medications like methotrexate or long-term metformin can raise MCH. Honest reporting of alcohol intake is important - the GP is not judging, they are looking for a treatable cause.
Blood film (peripheral smear)
A blood film allows a haematologist or automated analyser to look directly at the red cells. Hypersegmented neutrophils (5+ lobes) are pathognomonic for megaloblastic change from B12 or folate deficiency. Oval macrocytes (B12/folate) look different from round macrocytes (alcohol, liver disease, hypothyroidism).
Reticulocyte count if acute blood loss or haemolysis suspected
A high reticulocyte count confirms the bone marrow is responding to recent blood loss or haemolysis and explains the transient MCH elevation. This distinguishes a reactive process from a nutritional or metabolic cause.
Haematologist referral if unexplained
If B12, folate, TSH, and liver tests are all normal, especially in a patient over 60, referral to a haematologist is warranted to exclude myelodysplastic syndrome (MDS) or another bone marrow disorder. MDS typically presents with persistent macrocytosis and may involve all three cell lines.
Reassurance for a Mildly Elevated MCH
A mildly elevated MCH (33-36 pg) in an adult who drinks regularly or has recently had a viral illness, started a new medication, or has a known hypothyroidism is rarely a cause for alarm. In most cases:
The B12 and folate levels come back normal
The TSH is normal
A clear benign explanation (alcohol, medication, recent illness) is identified
The MCH normalises on its own or with simple treatment (e.g. B12 supplement, reduced alcohol)
Once you know the cause, tracking MCH over time is the best way to confirm treatment is working. Upload your follow-up blood test to SmarterBlood to see the trend and get a plain-English explanation of every marker in your panel — not just MCH.
High MCH - Frequently Asked Questions
What does high MCH mean on a blood test?
High MCH (mean corpuscular haemoglobin) means each of your red blood cells contains more haemoglobin than normal. The normal range in Australian labs is roughly 27-33 picograms (pg) per cell. High MCH almost always accompanies a high MCV (large red cells) because bigger cells naturally hold more haemoglobin. The most common causes are vitamin B12 deficiency, folate deficiency, alcohol use, and hypothyroidism.
What is the normal range for MCH in Australia?
The normal MCH range in Australian pathology laboratories is approximately 27-33 picograms (pg). Some labs use 27-32 pg or 26-34 pg. Values above 33-34 pg are considered elevated (hyperchromia). Values above 38 pg strongly suggest a significant B12 or folate deficiency driving macrocytosis.
What is the difference between MCH, MCV, and MCHC?
MCV (mean corpuscular volume) measures the average SIZE of your red blood cells in femtolitres (fL). MCH (mean corpuscular haemoglobin) measures the average AMOUNT of haemoglobin per red cell in picograms (pg). MCHC (mean corpuscular haemoglobin concentration) measures how concentrated the haemoglobin is within each cell, expressed as g/L. MCH and MCV usually rise and fall together because bigger cells hold more haemoglobin. MCHC is rarely elevated - true hyperchromia on MCHC usually suggests a lab artefact.
Can a high MCH be caused by alcohol?
Yes. Regular alcohol use is one of the most common causes of mildly elevated MCH, because it raises MCV (cell size) through direct bone marrow toxicity and folate interference, and MCH rises in parallel with MCV. MCH typically returns to normal within 2-4 months of reducing alcohol intake to within Australian NHMRC guidelines.
Is high MCH serious?
Mildly elevated MCH (33-38 pg) with no symptoms is rarely an emergency but always worth investigating. The most important causes - B12 deficiency and folate deficiency - are both easily treated but can cause permanent nerve damage (B12) or complicate pregnancy (folate) if missed for months. A high MCH on its own does not usually indicate cancer, though myelodysplastic syndrome should be excluded in older adults if no benign cause is found.
What tests will my GP order after high MCH?
Your GP will typically check serum B12, red cell folate, thyroid function (TSH), liver function tests including GGT, and often a reticulocyte count. If B12 is borderline, an active B12 (holotranscobalamin) or methylmalonic acid test may be added. A blood film may be requested to look for hypersegmented neutrophils, which are a hallmark of megaloblastic anaemia from B12 or folate deficiency.
Can lab artefacts cause a falsely high MCH?
Yes. Several lab conditions can falsely elevate MCH: severe lipaemia (very high triglycerides in the sample), cold agglutinins (antibodies that clump red cells in cold temperatures - more common in older adults), very high white cell counts (which absorb light at the measurement wavelength), and very high haemoglobin S in sickle cell disease. If your MCH is unexpectedly high with no obvious clinical cause, your GP may request a repeat with a fresh sample.
Related Reading
Got Your Blood Test Results?
Upload your full blood count PDF and SmarterBlood will explain every marker — MCV, MCH, MCHC, RDW, haemoglobin — in plain English with Australian reference ranges and trend tracking so you can see how your results change over time.
This page provides general educational information about elevated MCH (mean corpuscular haemoglobin). It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your GP about abnormal blood test results — they have access to your full medical history and can interpret your results in context. SmarterBlood does not provide medical care.