MCHC (mean cell haemoglobin concentration) explained

MCHC tells you how concentrated the haemoglobin is within the red cells. Think of a glass of squash: MCH is how much concentrate went into each glass, whereas MCHC is how strong the drink tastes once the glass size is taken into account. Lab Tests Online UK describes MCHC as the concentration of haemoglobin within red blood cells, and says it helps doctors interpret MCH results and diagnose specific red cell disorders.

It is calculated from haemoglobin and haematocrit, so it depends on two other measurements. The figure is expressed in grams per litre or grams per decilitre depending on the laboratory, and your own report lists the interval used.

MCHC arrives automatically with the full blood count, along with MCV, MCH and RDW. Together these four indices, described by Lab Tests Online UK as relating to the volume, size and haemoglobin content of the cells, help in the diagnosis or monitoring of anaemia, iron or B12 deficiency and thalassaemia.

In everyday practice MCHC is the least used of the indices. Doctors often glance at MCV first, then MCH, and consult MCHC when they want to confirm that cells really are pale or when a result looks odd.

No preparation is needed; blood is taken from a vein in the arm. Because MCHC is calculated, errors in either haemoglobin or haematocrit feed straight into it. Samples with a lot of fat in the blood, clumped red cells or other interfering factors can produce a falsely high figure, and a laboratory scientist will usually check a surprising MCHC by looking at a blood film or repeating the test.

Recent transfusion, medicines and vitamin or mineral deficiencies can alter red cell measurements, as Lab Tests Online UK notes in its full blood count guide.

Lab Tests Online UK says a low MCHC is seen in iron deficiency anaemia, long-standing inflammation and thalassaemia. These conditions share a common feature: the marrow cannot make enough haemoglobin, so the cells are pale. In iron deficiency this is because iron is a building block of haemoglobin.

The NHS explains that iron deficiency anaemia is often caused by blood loss or pregnancy, that heavy periods and bleeding in the stomach or intestines are common causes, and that GPs use a full blood count to check for it. It also describes thalassaemia as a group of inherited conditions affecting haemoglobin, noting that carriers may have smaller than usual red cells and a slightly lower haemoglobin.

Genuinely high values are unusual because a cell can only hold so much haemoglobin. Lab Tests Online UK states that a high MCHC is seen in conditions such as hereditary spherocytosis, in which red blood cells are an unusual shape. Spherical cells have less surface for their volume and tend to appear dense.

More often a high MCHC is an artefact. Cold-reacting antibodies that clump red cells, very high lipid levels in the sample, or very high white cell counts can mislead the analyser. For that reason a high MCHC is first checked for sample problems before being treated as a real finding.

An abnormal MCHC leads to the same tests as other red cell index changes: iron studies, B12 and folate, a blood film and sometimes a reticulocyte count. Where spherocytes are seen, further tests for haemolysis or an inherited red cell membrane disorder may follow.

Remember that red cell indices change slowly, so a repeat test shortly after an abnormal result is more useful when the sample may have been faulty than when the underlying cause is a real deficiency.