A high MCHC means your red blood cells are carrying more hemoglobin than usual relative to their size. The normal range for MCHC is 32 to 36 g/dL, so anything above 36 g/dL is considered elevated. In many cases, a high reading is simply a lab error. But when the result is real, it points to a handful of specific conditions where red blood cells are either misshapen or being destroyed faster than normal.
What MCHC Actually Measures
MCHC stands for mean corpuscular hemoglobin concentration. It tells you the average concentration of hemoglobin packed inside each red blood cell. Your lab calculates it by dividing your hemoglobin level by your hematocrit (the percentage of your blood that’s made up of red blood cells). It’s one of several red blood cell indices on a complete blood count (CBC), and on its own it doesn’t diagnose anything. It’s a clue that guides your doctor toward additional testing.
The reason MCHC matters is that hemoglobin is the protein responsible for carrying oxygen. When each red blood cell is overstuffed with hemoglobin, the cells tend to be dense, rigid, and fragile. They break apart more easily, which can lead to anemia and a cascade of related symptoms.
The Most Common Cause: A Lab Error
Before assuming something is wrong, it’s worth knowing that falsely elevated MCHC is one of the most common spurious findings on a CBC. Several things can interfere with the measurement:
- Lipemia (high fat levels in the blood sample) creates turbidity that artificially inflates the hemoglobin reading, pushing MCHC above normal.
- Cold agglutinins, which are antibodies that cause red blood cells to clump together when the sample cools, falsely lower the red blood cell count and hematocrit while raising the MCHC. Labs using automated analyzers will sometimes flag MCHC values above 36 or 37 g/dL specifically because cold agglutinins are so common.
- Hemolyzed samples, where red blood cells break open during the blood draw or transport, release hemoglobin into the surrounding fluid. The hemoglobin measurement stays the same, but the hematocrit drops, making the calculated MCHC artificially high.
If your MCHC is only slightly above 36 g/dL and your other blood values look normal, your doctor may simply repeat the test before investigating further. A truly high MCHC that persists across multiple draws is what warrants a closer look.
Hereditary Spherocytosis
Hereditary spherocytosis is one of the most well-known causes of a genuinely elevated MCHC. It’s a genetic condition where proteins in the red blood cell membrane are deficient or dysfunctional. Normally, red blood cells are shaped like a flexible disc, but in this condition the membrane loses surface area, and the cells become small, dense spheres called spherocytes. Because the same amount of hemoglobin is packed into a smaller, rounder cell, the concentration per cell goes up.
These spherocytes are rigid and fragile. The spleen, which filters out abnormal blood cells, traps and destroys them at a much higher rate than normal. This ongoing destruction causes anemia, jaundice (a yellowing of the skin and whites of the eyes), and an enlarged spleen. About half of people with hereditary spherocytosis develop gallstones, typically between late childhood and mid-adulthood, because the breakdown of so many red blood cells floods the body with bilirubin, a waste product that can crystallize in the gallbladder.
The condition ranges from mild to severe. Mild forms may go unnoticed until a routine blood test picks up the elevated MCHC and mild anemia. Severe forms cause life-threatening anemia that requires frequent blood transfusions and significant spleen enlargement. Diagnosis usually involves a family history review, since the condition is inherited from a parent, and a blood smear showing the characteristic spherocytes. Genetic testing is typically unnecessary. Treatment for milder cases focuses on folic acid supplementation to support red blood cell production, while severe cases may require surgical removal of the spleen.
Autoimmune Hemolytic Anemia
In autoimmune hemolytic anemia, your immune system produces antibodies that attack your own red blood cells. The damaged cells lose bits of their membrane as the immune system chips away at them, and they shrink into dense, sphere-like shapes, much like what happens in hereditary spherocytosis. The result is the same: a higher hemoglobin concentration per cell and an elevated MCHC.
This condition sometimes appears on its own without a clear trigger. Other times it develops alongside autoimmune diseases like lupus, blood cancers like lymphoma, or as a reaction to certain medications. Symptoms include fatigue, paleness, weakness, jaundice, fever, fainting, and abdominal discomfort from an enlarged spleen. The onset can be sudden and dramatic or slow and gradual.
Treatment typically starts with corticosteroids to suppress the immune response. If the red blood cell destruction is severe, blood transfusions or surgical removal of the spleen may be necessary.
Severe Burns
Extensive burns can cause a genuinely elevated MCHC through a different mechanism. Severe heat damage dehydrates red blood cells, shrinking their volume while the hemoglobin inside remains the same. The concentration per cell rises as a result. This is a situational cause that’s usually obvious from the clinical context, not something discovered unexpectedly on routine blood work.
Symptoms to Pay Attention To
A high MCHC by itself doesn’t produce symptoms. What you feel comes from the underlying condition causing it, and the most common thread is anemia from red blood cell destruction. Symptoms that often accompany a high MCHC include:
- Fatigue and weakness from reduced oxygen delivery to your tissues
- Pale skin and gums
- Rapid or irregular heartbeat, as your heart compensates for fewer red blood cells
- Shortness of breath, especially with exertion
- Dizziness or headaches
- Jaundice, a yellow tint to your skin and eyes from the breakdown products of destroyed red blood cells
- Chest pain in more severe cases
If you have a high MCHC with no symptoms and normal hemoglobin levels, the result is more likely a lab artifact than a sign of disease.
What Happens After a High Result
Your doctor’s next step depends on how high the value is and what the rest of your CBC looks like. A repeat blood draw is common, especially if the elevation is modest. If the result holds, a peripheral blood smear is one of the most useful follow-up tests. This involves examining your blood under a microscope to look for spherocytes or other abnormally shaped cells. A reticulocyte count, which measures how quickly your bone marrow is producing new red blood cells, helps determine whether your body is trying to compensate for ongoing cell destruction.
If autoimmune hemolytic anemia is suspected, a direct antiglobulin test (sometimes called a Coombs test) checks for antibodies attached to your red blood cells. For hereditary spherocytosis, your doctor will ask about family history and may order an osmotic fragility test, which measures how easily your red blood cells burst when placed in diluted solutions. The pattern of results across these tests, combined with your symptoms and history, is what leads to a specific diagnosis.