MCHC: what it is, what it tells you and what a low level means

MCHC shows how concentrated the haemoglobin inside your red cells is. If it is low, iron is often short. If it is high, a problem with the sample is more likely than an illness. And if it is just outside the limits while everything else is normal, it usually does not matter.

Why we test it

It is worked out by dividing haemoglobin by haematocrit, the share of your blood made of red cells. So it shows how full of haemoglobin your red cells are.

In healthy people it barely changes, from one person to the next or over time. That is why a value outside the limits first means checking that the measurement is right.

It can drop when the lack of iron is marked, usually together with MCV and MCH.

What it tells you, and what it does not

If it is low, there is often a marked lack of iron. In that case MCV and MCH are usually low too.

If it is high, it is rarely a red cell disease. More often something disturbed the measurement, and a new sample clears it up.

On its own it says little: it is calculated from haemoglobin and haematocrit, and it inherits their errors.

That is why it is read together with other tests:

• MCV: How big your red cells are
• MCH: How much haemoglobin a red cell holds
• Haemoglobin: Whether there is anaemia
• Ferritin: Whether iron is short

Normal MCHC levels

The lab decides what is normal. It is usually 32 to 35 g/dL, the same for women and men. Your own report may print different limits.

Some labs print it in g/L instead of g/dL: the number is ten times bigger, but it means the same.

In the Rosa report you also see your optimal range, read together with MCV, MCH and ferritin.

What your result means

Find the row for your result, in g/dL. Which values are dangerous? On its own, MCHC usually is not: what counts is whether haemoglobin, MCV or ferritin are out of range too.

• Below your report’s limit, Usually below 32: Low. It often means a marked lack of iron. If it is just below and everything else is normal, it usually does not matter. Check your haemoglobin, MCV and ferritin too. If any of them is out of range, talk to your doctor.
• Within your report’s limits, Usually 32 to 35: Normal. Usually fine. On its own it does not show whether your iron is fine. In the Rosa report you also see whether you are in your optimal range.
• Above your report’s limit, Usually above 35: High. More often a problem with the sample than an illness. If it is just above and everything else is normal, it usually does not matter. If it is well above the limit, or other results are out of range too, show your doctor the report. They usually have the test repeated.

If your MCHC is low or high

• Low MCHC: Iron is often short, but if everything else is normal it usually does not matter. The causes are below.
• High MCHC: More often a problem with the sample than an illness. More on this below.

Low MCHC: the causes

It is an uncommon finding, and MCV and MCH are usually low too.

• Too little iron: When the lack is marked, red cells come out small and not very full of haemoglobin. Heavy periods, pregnancy or too little iron in your diet are common reasons.
• Hidden blood loss: Small losses from the gut that you cannot see. In men and after menopause, they are the first thing doctors look for.
• A small variation: If it is just below the limit and everything else is normal, it may simply be the normal variability of the measurement.

High MCHC: often a technical problem

A high MCHC rarely means a red cell disease. More often something disturbed the measurement, and your doctor usually clears it up with a new sample. For example:

• Blood very rich in fats such as triglycerides, which makes the sample cloudy.
• Red cells breaking open in the tube.
• Cold agglutinins: antibodies that make red cells stick together in the cold.

More rarely some medicines or severe imbalances of the salts in your blood are involved. Rarely, spherocytosis: an inherited condition in which red cells are small spheres instead of discs.

When to worry

Talk to your doctor if:

• It is low and your haemoglobin or ferritin is low too.
• It is well above the limit, or other results are out of range too: your doctor usually has the test repeated, and looks for the cause if it stays high.
• You are a man, or a woman after menopause, and iron is short.
• Your skin or the whites of your eyes turn yellow, or your urine is very dark: see a doctor today.
• You see black stools or blood in your stools: call 112 or go to the emergency department.
• You are short of breath at rest, have chest pain or feel faint: call 112 or go to the emergency department.

Frequently asked questions

Slightly low MCHC but everything else normal: should I worry? Usually not. If your haemoglobin, MCV, MCH and ferritin are normal, it may just be a small variation in the measurement. Show the report to your doctor at your next check-up.

High MCHC: is it serious? Usually not. More often it is a problem with the sample, and with a new sample the value comes back to normal. If it stays high, your doctor looks for the cause.

What are cold agglutinins? Antibodies that make red cells stick together in the cold. In the tube they upset the count and push MCHC up: the lab can correct it by warming the sample. Your doctor decides whether the antibodies themselves need looking into.

Do I need to fast for an MCHC test? Not for MCHC itself. It is usually done with other tests that do need fasting, though, so it is best to arrive fasted. You can drink water.

How often should it be checked? For people who feel well there is no fixed rule: Rosa measures it twice a year, with the blood count. If it is out of range, your doctor decides whether and when to repeat it.

Sources

• Zandecki and colleagues, spurious results on haematology analysers: red cells, haemoglobin and red cell indices. International Journal of Laboratory Hematology, 2007. PMID 17224005
• Falvella and colleagues, an automatic reflex test to spot a falsely high MCHC caused by cold agglutinins. Scandinavian Journal of Clinical and Laboratory Investigation, 2021. PMID 34346820
• de Jonge and colleagues, how red cells breaking open in the tube change the blood count. Journal of Clinical Laboratory Analysis, 2018. PMID 29396875
• Liao and colleagues, blood count values for screening and diagnosing hereditary spherocytosis. Journal of Clinical Laboratory Analysis, 2019. PMID 30945356
• British Society of Gastroenterology, guidelines for iron deficiency anaemia in adults. Gut, 2021. PMID 34497146