Low MCHC Explained
What mean corpuscular haemoglobin concentration measures, why a low result means hypochromia, and how iron deficiency is told apart from thalassaemia trait.
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The Quick Answer
MCHC stands for mean corpuscular haemoglobin concentration. It tells you how densely haemoglobin, the oxygen-carrying pigment inside red blood cells, is packed into the average red cell. It is calculated by dividing your haemoglobin level by your haematocrit, the proportion of your blood volume made up of red cells.
A result below the normal range means your red cells are, on average, more sparsely filled with haemoglobin than they should be. This is called hypochromia, and the two causes responsible for the great majority of Australian cases are iron deficiency and thalassaemia trait.
Read MCHC with the other two indices: it is most useful alongside MCH (the amount of haemoglobin per cell) and MCV (the size of the cell). A low MCHC almost always travels with a low MCH, and often a low MCV too, because all three reflect the same underlying shortfall in haemoglobin production.
MCV, MCH and MCHC: Three Different Questions About the Same Cell
These three red cell indices are calculated from the same full blood count sample but each answers a different question about the average red blood cell.
MCV
Mean Corpuscular Volume
The average SIZE of a single red blood cell, reported in fL (femtolitres).
MCH
Mean Corpuscular Haemoglobin
The average AMOUNT of haemoglobin carried inside one red blood cell, reported in pg (picograms).
MCHC
Mean Corpuscular Haemoglobin Concentration
The average CONCENTRATION of haemoglobin packed into the red cell, calculated as haemoglobin divided by haematocrit, reported in g/L (grams per litre).
Why a Low MCHC Means Hypochromia
Haemoglobin is what gives a red blood cell its colour under the microscope. The central area of a normal cell already appears paler than the outer rim, because red cells are shaped like a flattened disc, thinner in the middle. When a cell is genuinely under-filled with haemoglobin, that central pale area widens and the whole cell stains more faintly overall. A laboratory scientist reviewing the blood film describes this as hypochromia, and will usually grade it as mild, moderate or marked.
Hypochromia describes a finding rather than naming a cause. Both the MCHC number and the appearance on the film point to the same underlying process: something has interfered with the normal manufacture of haemoglobin inside developing red cells in the bone marrow. Identifying what has interfered is the point of the investigations below.
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Iron Deficiency or Thalassaemia Trait: How to Tell Them Apart
These two conditions cause a near-identical hypochromic, microcytic pattern on a basic full blood count, yet need entirely different management. The tests below are what separate them.
Serum ferritin
Low
Normal (can look high if there is coexisting inflammation)
Transferrin saturation
Low
Normal
RDW (red cell size variation)
High, cells vary widely in size
Usually normal, the small cells are uniform in size
Red cell count (RBC)
Low or low normal
Normal or high, often the first clue that raises suspicion
Mentzer index (MCV ÷ RBC)
Above 13
Below 13
Haemoglobin electrophoresis or HPLC
Normal pattern
Raised HbA2 (beta thalassaemia trait) or a specific alpha-globin gene deletion
Family and ethnic background
No particular pattern
Often Mediterranean, Middle Eastern, South Asian, South-East Asian or African ancestry, sometimes a relative with mild, unexplained anaemia
Causes of Low MCHC
Ordered roughly by how often each is seen in Australian general practice.
Iron deficiency
Not enough iron is available to build haem, so each red cell is packed with less haemoglobin than it should carry
By far the most common cause seen in Australian general practice, especially in menstruating women, pregnancy, vegetarians and vegans, and anyone with unexplained blood loss. Confirmed with a low serum ferritin and a low transferrin saturation.
Thalassaemia trait (alpha or beta)
An inherited reduction in production of one globin chain means red cells are made small and pale, even though iron stores are entirely normal
The second most common cause of a hypochromic, microcytic picture in Australia, particularly in people of Mediterranean, Middle Eastern, South Asian, South-East Asian or African family background. Ferritin and transferrin saturation are normal. Confirmed with haemoglobin electrophoresis or HPLC.
Anaemia of chronic disease, iron-restricted pattern
Ongoing inflammation raises hepcidin, a hormone that locks iron inside the body's stores and keeps it away from the bone marrow, even though total body iron is adequate
Seen with chronic infection, rheumatoid arthritis and other inflammatory conditions, inflammatory bowel disease, chronic kidney disease, and some cancers. Ferritin looks falsely reassuring because it also rises with inflammation, so it is read alongside CRP.
Sideroblastic anaemia
A fault in the final step of haem synthesis inside developing red cells in the bone marrow means iron accumulates in the cell without being properly built into haemoglobin
Uncommon. Can be inherited or acquired, and is associated with heavy alcohol use, certain medications including isoniazid, lead exposure, and myelodysplastic syndrome. Confirmed on bone marrow examination showing ring sideroblasts.
Lead exposure
Lead blocks two of the enzymes needed to build haem, producing the same pale, poorly haemoglobinised red cells as iron deficiency
Consider with renovation of homes built before the 1970s, battery or smelter work, imported cosmetics or traditional medicines, and in children with pica (eating non-food items). Confirmed with a blood lead level.
When Low MCHC Appears Alongside Low MCH and MCV, and When It Stands Alone
In the great majority of cases, a low MCHC turns up together with a low MCH and a low MCV. This makes biological sense: iron deficiency and thalassaemia trait both reduce the total amount of haemoglobin made per cell. That lowers the cell's haemoglobin content (MCH) and its concentration (MCHC), and, because red cells shrink to compensate, its overall size (MCV) as well. This combined pattern is sometimes called microcytic hypochromic anaemia.
A low MCHC appearing by itself, with a normal MCH and MCV, is less common and usually means one of two things. The first is an early or mild degree of iron deficiency, before enough abnormal cells have accumulated to lower the average size and haemoglobin content. The second is a measurement quirk on the automated analyser, for example when a very high white cell count or marked lipaemia in the sample interferes with the optical or electronic reading. Either way, an isolated low MCHC is still worth discussing with your GP rather than dismissing.
A Sample-Handling Artefact Worth Knowing, and Why It Does Not Explain a Low Result
Blood for a full blood count is collected into an EDTA tube, the anticoagulant that stops the sample clotting before it reaches the laboratory. If the tube is underfilled (not enough blood relative to the fixed amount of EDTA inside it), or if there is simply excess EDTA for the volume collected, red cells slowly shrink over the following hours as they are exposed to a relatively concentrated anticoagulant solution.
The important point for a low MCHC result is that this artefact typically pushes the numbers in the opposite direction, shrinking the MCV and producing a spuriously high MCHC, not a low one. So if your report shows a genuinely low MCHC, an underfilled tube is not the likely explanation, and the result should be taken seriously rather than assumed to be a collection problem. If your GP suspects any collection issue at all, the simplest fix is a repeat sample.
What Your GP Will Do Next
Confirm the pattern with a blood film
A laboratory scientist looks at the red cells directly under the microscope, grading how pale (hypochromic) and how small (microcytic) they are, and checking for other clues such as target cells, basophilic stippling, or fragmented cells that point away from a simple nutritional cause.
Iron studies: ferritin, iron, TIBC and transferrin saturation
Serum ferritin is the most sensitive marker of iron stores, and a low result confirms iron deficiency in most people. Ferritin is also an acute-phase reactant, so it is interpreted alongside CRP if inflammation or infection is a possibility.
Check RDW, red cell count, and calculate the Mentzer index
RDW and red cell count, read together with MCV, are the fastest way to separate iron deficiency from thalassaemia trait before any specialised test is ordered. The Mentzer index (MCV divided by red cell count) is a quick calculation many GPs use as a screening step.
Order haemoglobin electrophoresis or HPLC if thalassaemia is possible
Recommended when the Mentzer index is low, ferritin is normal despite small pale cells, or family or ethnic background raises suspicion. This test measures the proportions of different haemoglobin types and confirms or excludes thalassaemia trait.
Look for an iron-restricted, inflammatory pattern
If ferritin is normal or high but transferrin saturation is low and there is a plausible chronic illness, anaemia of chronic disease is considered. Persistently unexplained findings, or normal or high iron studies despite obvious hypochromia, may prompt consideration of sideroblastic anaemia or lead exposure.
Investigate the underlying cause of any confirmed iron deficiency
Iron deficiency is a finding, not a final diagnosis. Your GP will ask about diet, menstrual loss and pregnancy, and in adults, particularly men and postmenopausal women, or when there is no obvious explanation, will consider investigating the gastrointestinal tract for a source of blood loss.
Treat the diagnosed condition rather than the low number alone
Confirmed iron deficiency is treated with iron replacement and a plan to address its cause, with a repeat full blood count to confirm response. Thalassaemia trait needs no iron at all, no ongoing supplementation, and instead benefits from genetic counselling and, if relevant, partner testing before starting a family. Iron should never be taken as an open-ended, indefinite supplement without a diagnosed and understood cause.
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Full Blood Count GuideWhen to Seek Urgent Care
Breathlessness, chest pain or a racing heart at rest
These can signal that anaemia has become severe enough to reduce oxygen delivery to the heart and other organs, and warrant same-day medical assessment rather than waiting for a routine appointment.
Black, tarry stools or visible blood in vomit or stool
A sign of possible gastrointestinal bleeding, which is one of the more serious causes of iron deficiency and needs prompt investigation rather than iron replacement alone.
A very low haemoglobin alongside the low MCHC (roughly below 80 g/L)
Severe anaemia combined with hypochromic red cells usually needs urgent review, and same-day care if there is dizziness, fainting or breathlessness at rest.
Abdominal pain, constipation or behavioural change in a child with pale, small red cells
Raises the possibility of lead exposure, which can affect development if missed, and warrants an urgent GP appointment and a blood lead level.
Unexplained bruising, frequent infections or bleeding alongside the abnormal red cell result
Suggests the bone marrow may not be producing white cells and platelets normally either, which points away from a simple nutritional cause and needs urgent haematology review.
Foods That Support Iron Stores, If Iron Deficiency Is the Confirmed Cause
This section applies only once iron deficiency has been confirmed on iron studies. If your low MCHC is due to thalassaemia trait, extra dietary iron provides no benefit and is not recommended.
Lean red meat (beef, lamb)
Haem ironHaem iron from meat is absorbed at roughly 15 to 35 per cent efficiency, far higher than iron from plant foods. Two to three serves a week meaningfully supports iron stores.
Liver (chicken, lamb)
Iron, B12, folateOne of the most concentrated food sources of iron available. Avoid in pregnancy because of its high vitamin A content.
Legumes (lentils, chickpeas, beans)
Non-haem ironA good plant source of iron. Soaking and rinsing dried legumes reduces the phytates that otherwise reduce iron absorption.
Leafy greens (spinach, silverbeet, kale)
Non-haem ironUseful supporting iron sources, best combined with a source of vitamin C at the same meal to improve absorption.
Citrus fruit and berries
Vitamin CVitamin C substantially improves the absorption of non-haem iron eaten at the same meal, so a glass of orange juice alongside a plant-based iron source is a practical habit.
Fortified breakfast cereals
IronA convenient additional source of iron, particularly useful for people on a largely plant-based diet.
Sources and reference ranges
Adult reference ranges on this page follow the AACB and RCPA harmonised reference intervals unless stated otherwise; the range printed on your own report always takes precedence because laboratories differ.
Low MCHC: Frequently Asked Questions
What does a low MCHC mean on a blood test?
MCHC stands for mean corpuscular haemoglobin concentration. It measures how densely haemoglobin is packed inside the average red blood cell, worked out by dividing your haemoglobin level by your haematocrit. The Australian reference interval is roughly 320 to 360 g/L. A result below about 310 to 320 g/L means your red cells are, on average, carrying less haemoglobin per unit of volume than normal, a state called hypochromia because the cells look pale under the microscope. In Australian general practice the two most common explanations are iron deficiency and thalassaemia trait, and your GP will usually order iron studies and look at the rest of your full blood count to tell them apart.
What is the difference between MCHC, MCH and MCV?
All three come from the same full blood count but measure different things. MCV is the average size of a red blood cell, in femtolitres. MCH is the average amount, or mass, of haemoglobin carried inside one red cell, in picograms. MCHC is the average concentration of that haemoglobin, worked out by dividing haemoglobin by haematocrit, and is expressed in grams per litre. In short: MCV is the size of the cell, MCH is the amount of haemoglobin inside it, and MCHC is how tightly that haemoglobin is packed for the cell size. Low MCHC and low MCH usually rise and fall together, because both reflect reduced haemoglobin production.
What is hypochromia and why do the cells look pale?
Hypochromia is the term used when red blood cells contain less haemoglobin than normal for their size, which is what a low MCHC represents numerically. Haemoglobin is the pigment that gives red cells their colour when stained and examined under a microscope, so cells with reduced haemoglobin content stain paler and often show a wider area of central pallor than a normal red cell. A laboratory scientist reviewing the blood film may describe this as mild, moderate or marked hypochromia. It describes a finding rather than naming a disease. The underlying problem is usually reduced haemoglobin synthesis from iron deficiency or an inherited thalassaemia trait.
What causes a low MCHC in Australia?
The two dominant causes seen in Australian general practice are iron deficiency, from causes such as menstrual blood loss, pregnancy, a low-iron diet or gastrointestinal bleeding, and thalassaemia trait, an inherited condition common in people of Mediterranean, Middle Eastern, South Asian, South-East Asian and African family background. Less commonly, a low MCHC can reflect anaemia of chronic disease with iron-restricted red cell production, sideroblastic anaemia, where the bone marrow cannot build iron into haemoglobin properly, or lead exposure, which blocks the same haem-building pathway. Your GP narrows these down with iron studies, a blood film, red cell count, RDW and sometimes haemoglobin electrophoresis.
How can I tell if my low MCHC is iron deficiency or thalassaemia trait?
The two conditions look similar on a basic full blood count but separate clearly on further testing. Iron deficiency typically shows a low ferritin, a low transferrin saturation, a high RDW because cell sizes vary widely, and a red cell count that is normal or low. Thalassaemia trait typically shows a normal ferritin and transferrin saturation, a normal RDW because the small cells are uniformly sized, and a red cell count that is normal or even higher than expected for the haemoglobin level. The Mentzer index, MCV divided by red cell count, is a simple screening calculation your GP can do: below 13 suggests thalassaemia trait, above 13 suggests iron deficiency. Haemoglobin electrophoresis confirms thalassaemia trait.
Can I have a low MCHC without being anaemic?
Yes. MCHC and MCH can fall before haemoglobin itself drops low enough to be labelled anaemia, particularly in early or mild iron deficiency, and thalassaemia trait often causes a lifelong mildly low MCHC without any significant anaemia at all. A low MCHC on a routine blood test, even alongside a normal haemoglobin, is still worth investigating with iron studies, because it can be an early sign of developing iron deficiency and because thalassaemia trait carries implications for family planning and for relatives who may carry the same inherited trait. It should not be dismissed just because you feel well or your haemoglobin result looks normal.
Should I start taking iron supplements if my MCHC is low?
Not without a confirmed diagnosis. A low MCHC on its own does not tell you whether iron deficiency or thalassaemia trait is responsible, and taking iron for thalassaemia trait provides no benefit and can, over years, contribute to iron overload, particularly if repeated unnecessarily. The safe approach is to have ferritin and transferrin saturation checked first. If they confirm true iron deficiency, your GP will also want to find out why, through diet history, menstrual history or, in some cases, investigation of the gastrointestinal tract, rather than treating the low ferritin in isolation indefinitely. Iron should never be taken as an ongoing, open-ended supplement without a diagnosed and understood cause.
Can a badly filled blood tube cause a falsely low MCHC?
Not usually in this direction. Sample-handling problems, such as an underfilled EDTA tube where too little blood is collected relative to the anticoagulant, are a recognised cause of artefact in the full blood count, but they typically shrink red cells over the following hours and push MCHC and MCV artificially higher, not lower. A genuinely low MCHC on a properly filled, promptly processed sample is not usually explained away by a tube-filling problem, and should be taken at face value and investigated rather than repeated in the hope that it was simply a laboratory error.
When should I see a doctor urgently about a low MCHC result?
Most low MCHC results reflect a straightforward and treatable cause such as iron deficiency, so urgent review is the exception rather than the rule. Seek prompt medical attention if you have breathlessness, chest pain or a racing heart at rest, black or tarry stools or blood in your vomit or stool, a very low haemoglobin alongside the low MCHC, or unexplained bruising, infections or bleeding occurring together with the abnormal red cell result. In a child, abdominal pain, constipation or behavioural changes alongside a hypochromic blood picture should prompt consideration of lead exposure and an urgent GP appointment.
Related Reading
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This page provides general educational information about low MCHC and hypochromia. It is not a substitute for professional medical advice, diagnosis, or treatment. Always discuss an abnormal blood test result with your GP, who has access to your full medical history and can interpret your results in context. SmarterBlood does not provide medical care.