What Does a Low MCHC on a Blood Test Mean?

A low MCHC means the report suggests your red blood cells hold less concentrated haemoglobin than the laboratory expects. MCHC (mean corpuscular haemoglobin concentration) is one of the red cell indices in a full blood count, also called a complete blood count. MedlinePlus lists iron deficiency anaemia and thalassaemia as causes of a low MCHC.

MCHC is one clue, not a diagnosis. Clinicians read it together with haemoglobin, the other red cell indices, your symptoms and further tests. This guide focuses on what MCHC adds. Separate SameCase guides cover low MCV and MCH and high RDW in more depth.

A low MCHC is often found on a routine test, but the possible causes include blood loss, so some symptoms should not wait for a planned review. The NHS advises urgent help through NHS 111 or an urgent GP appointment if your poo is black or dark red, or if you have bloody diarrhoea; elsewhere, use your local urgent care service. It advises emergency care if bleeding will not stop or there is a lot of blood.

Also get help sooner for:

• Vomiting blood, or black or tarry stools.
• Very heavy periods with dizziness, faintness or breathlessness.
• Chest pain or discomfort, a racing or irregular heartbeat, or severe breathlessness. Call your local emergency number if these are severe or sudden.
• Unexplained weight loss or a change in bowel habit alongside a low iron result.

MedlinePlus gives a typical adult range of 32 to 36 g/dL, which is the same as 320 to 360 g/L. It notes that normal ranges vary slightly between laboratories. Use the range printed on your own report and check the units, since some laboratories use g/dL and others g/L.

A result just below the range, with normal haemoglobin and other indices, may be interpreted differently from a clearly low MCHC alongside anaemia. Ask your clinician which applies to you rather than judging from the number alone.

Hypochromia means red blood cells look paler than normal when examined under a microscope. MedlinePlus explains that this usually happens when there is not enough haemoglobin, the oxygen-carrying pigment, in the cells. A low MCHC is the number that often goes with this appearance.

Your report may use the word hypochromic, especially if a blood film was examined. Cleveland Clinic notes that most anaemias with small red cells (microcytic anaemias) are also hypochromic, which is why a low MCHC is often seen alongside a low MCV and MCH.

Iron deficiency is the most common cause of hypochromia, according to MedlinePlus. Other causes listed by Cleveland Clinic for small, pale red cells include:

These causes can overlap. Someone with a long-term inflammatory condition can also become low in iron, and a thalassaemia trait can sit alongside iron deficiency. In anaemia of chronic disease, the American Family Physician review notes that blood iron is usually low while ferritin is typically normal or raised, which is one way clinicians tell it apart from simple iron deficiency. This is why the full set of results, rather than MCHC alone, guides the next step.

• Iron deficiency, for example from heavy periods, bleeding in the gut, pregnancy or too little iron in the diet.
• Thalassaemia traits and other inherited conditions that affect haemoglobin production.
• Anaemia of chronic disease, linked to long-term inflammation, chronic infection, autoimmune disease, cancer or chronic kidney disease.
• Rarer causes such as sideroblastic anaemia and lead poisoning.

If iron deficiency is suspected, ferritin is often the first test. The American Family Physician review recommends serum ferritin first when red cells are small, with low ferritin suggesting iron deficiency. Ferritin can be raised by liver disease, cancer, chronic kidney disease and other inflammatory states, so a normal ferritin does not always rule iron deficiency out.

Finding iron deficiency is only half the answer. The NHS lists heavy periods, pregnancy and bleeding from the gut as common reasons. The same review says iron deficiency in adults is presumed to come from blood loss until shown otherwise, and that cancer of the digestive tract must be ruled out in men and in women who no longer have periods. A stool test or a referral may be suggested. Talk to a clinician before starting iron supplements, so that the reason for the low iron is still looked for.

RDW (red cell distribution width) shows how much your red cells vary in size. The American Family Physician review notes that RDW is often raised in iron deficiency but usually normal in anaemia of chronic disease. A low MCHC with a high RDW can therefore fit with iron deficiency.

This pattern is not proof. The same review says RDW is not reliable enough on its own to tell iron deficiency apart from beta thalassaemia trait, where the red cell count is often high-normal. Ferritin, iron studies and sometimes haemoglobin testing are used to sort this out.

Take the full report, including MCHC, haemoglobin, MCV, MCH, RDW, red cell count, units and the reference range, plus any earlier results. These questions can help:

• Is my haemoglobin low, or is the low MCHC an isolated finding?
• Do my MCV, MCH and RDW point towards iron deficiency or another cause?
• Has my ferritin been checked, and could inflammation be affecting it?
• If I am low in iron, what is the most likely reason, and does it need investigating?
• Is a thalassaemia trait possible, given my family background?
• When should the blood count be repeated, and what result would change the plan?
• Should I wait for advice before taking any iron or other supplements?

On SameCase, patients and verified doctors share de-identified cases. Reading how others with a low MCHC had their ferritin, RDW and possible sources of blood loss looked into can help you spot questions to bring to your appointment.

Similar cases help you prepare; they do not explain your own result. Every person's history, symptoms and blood tests differ, so bring your questions to the clinician who can see your full results.