MCHC blood test: what high or low MCHC means

What MCHC measures

MCHC is the average concentration of hemoglobin in a given volume of red cells, reported in grams per deciliter (g/dL). Labs usually calculate it from your hemoglobin and hematocrit.

It is one of the red cell indices. MCH is the amount of hemoglobin in one cell; MCHC takes the size of the cell into account, so it shows how densely packed that hemoglobin is. MCV (cell size) and RDW (size variation) complete the picture.

MCHC stays fairly steady in most people, so it changes later than MCV and MCH and is rarely the first clue.

What a low MCHC can mean

A low MCHC means hypochromic cells: paler than usual because they hold less hemoglobin for their size. Common causes:

• Iron deficiency. The most common cause, often from blood loss such as heavy periods or bleeding in the gut. MCHC tends to fall later than MCV, so check ferritin first; see ferritin levels.
• Thalassemia trait and other inherited hemoglobin differences.
• Long-term inflammation, from ongoing infection, kidney or liver disease, or cancer.

What a high MCHC can mean

Red cells can only pack so much hemoglobin, so an MCHC above the lab range is unusual. When it is real, it usually means the cells have lost water or shape. Possible causes:

• Hereditary spherocytosis, an inherited condition where red cells are round instead of disc-shaped and break down early.
• Autoimmune hemolytic anemia, where the immune system destroys red cells.
• A lab artifact. Red cells clumping together in a cold sample, or cells breaking open in the tube, can throw off the reading. Many clinicians simply repeat the test first.

A high MCHC is never a sign of extra-healthy blood. If it stays high on a repeat test, ask about a blood smear and tests for red cell breakdown.

What to do with an abnormal result

1. Read it with the rest of the CBC. Hemoglobin and hematocrit show whether you are anemic; MCV and MCH usually tell the clearer story.
2. For a low MCHC, ask about ferritin and an iron panel. If iron is normal, ask whether hemoglobin electrophoresis (a thalassemia check) makes sense.
3. For a high MCHC, ask whether to repeat the CBC. If it stays high, a blood smear, reticulocyte count and tests for red cell breakdown are the usual next steps.
4. Compare within one lab. MCHC differs a little between analyzers, so trends mean more than a single value.

See a clinician promptly if an abnormal MCHC comes with yellowing of the skin or eyes, dark urine, shortness of breath, chest pain, fainting, black or bloody stools, or very heavy periods.