MCH blood test: what high or low MCH means

What MCH measures

Hemoglobin is the protein in red blood cells that carries oxygen. MCH is the average weight of hemoglobin in one red cell, reported in picograms (a trillionth of a gram).

MCH is one of the red cell indices. It tracks closely with MCV, the average size of a red cell, because bigger cells hold more hemoglobin and smaller cells hold less. MCHC adjusts for size and shows how concentrated the hemoglobin is, and RDW shows how much cell sizes vary. A clinician reads them together.

Because MCH moves with MCV, it rarely adds much on its own. Its job is to confirm the pattern: small, pale cells or large ones.

What a low MCH can mean

A low MCH points to hypochromic cells (paler than usual, carrying less hemoglobin), usually alongside small cells. Common causes:

• Iron deficiency. The most common cause. It often comes from blood loss, such as heavy periods or bleeding in the gut. Check it with ferritin and an iron panel; see ferritin levels.
• Inherited hemoglobin differences, such as thalassemia trait.
• Long-term inflammation, from ongoing infection, kidney or liver disease, or cancer, which limits how the body uses iron.

Like MCV, MCH is a late sign of low iron. Ferritin falls first, so a normal MCH does not rule out low iron. A low-normal MCH is still worth a ferritin check, which is one reason Gabriel tracks an optimal range as well as the lab range.

What a high MCH can mean

A high MCH usually goes with a high MCV: larger red cells holding more hemoglobin each. Common causes:

• Low vitamin B12 or folate, or trouble absorbing them. Both are needed to build red cells.
• Long-term heavy drinking.
• Thyroid problems, especially an underactive thyroid.
• Liver disease.
• Medications and treatments, including some chemotherapy.

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, MCHC and RDW narrow down the type.
2. Ask about the follow-up tests that fit. For a low MCH that usually means ferritin and an iron panel. For a high MCH, vitamin B12, folate, thyroid (TSH) and liver tests.
3. Bring your medication list and drinking habits to the conversation.
4. Retest after a change. Red cells live about 120 days, so MCH moves slowly. A recheck after about three months shows whether a fix is working.

See a clinician promptly if an abnormal MCH comes with shortness of breath, chest pain, a racing or irregular heartbeat, fainting, black or bloody stools, very heavy periods, or numbness and tingling in your hands or feet.