A high MCV and MCH on a blood count mean your red blood cells are running larger than usual, and a single cause raises both numbers together. So the useful question is what is making your cells big. In most adults the answer is something everyday: low B12 or folate, alcohol, liver or thyroid trouble, a medicine, or smoking. Because red cells live for months, a high reading usually reflects your habits and health over the past few months rather than last week.
What MCV and MCH Measure on Your Report
Your report lists MCV, the average volume of your red cells, measured in femtoliters (fL). A typical adult range is about 80 to 100 fL. MCH is the average amount of hemoglobin, the oxygen-carrying protein, in each red cell.1Personalabs. High MCV Blood Test: Causes, Symptoms & What To Do It is calculated from your hemoglobin and red cell count, so larger cells simply hold more.2Free Medical Textbook. CHAPTER 2 EXAMINATION OF THE BLOOD Large red cells can appear with or without anemia.
On your printout, an H next to MCV and MCH usually appears with a normal hemoglobin and red cell count. Large cells with normal hemoglobin means there is no anemia yet, which often makes this an early finding. The number matters too: 101 fL means something different from 115 fL, because higher values narrow the likely causes. Labs set slightly different ranges, so compare your result against the range printed on your own report. High MCH does not mean too much iron or hemoglobin overload. It reflects cell size. An MCV above 100 fL turns up in fewer than 2 in 100 people in the general population.3PubMed Central. Acquired Myelodysplasia or Myelodysplastic Syndrome: Clearing the Fog
Low Vitamin B12 or Folate
Most cases of large red cells trace back to a problem copying DNA in the bone marrow, where red cells are made.4Cleveland Clinic Journal of Medicine. Increased mean corpuscular volume A cell that is slow to copy its DNA divides late, so it keeps growing and comes out abnormally large.5Cleveland Clinic Journal of Medicine. Increased mean corpuscular volume Low B12 and low folate are the two classic causes of this.6Cleveland Clinic Journal of Medicine. Increased mean corpuscular volume
The two are linked. B12 is needed to switch folate into its working form, so a B12 shortage also leaves you short of usable folate.7PubMed Central. Diagnosis and treatment of macrocytic anemias in adults That means a normal folate reading doesn’t rule out a B12 problem.
B12 shortages are common in vegans, older adults, people with pernicious anemia, and long-term users of metformin or stomach acid reducers. Low folate is linked to poor diet, heavy drinking, and the extra needs of pregnancy.
These shortages can go unnoticed for a long time. The body stores a large reserve of B12, mostly in the liver, so a shortage usually builds over months to years. Folate reserves are much smaller and can run down within a few months of a poor diet or heavy drinking. Because the marrow keeps producing cells while they slowly enlarge, MCV can creep up on a routine count well before hemoglobin falls or symptoms start.
Many people have no symptoms when MCV is first flagged. Tiredness and breathlessness appear once anemia develops. Pins and needles in the hands or feet, poor balance, or memory trouble point toward B12, and a sore, smooth tongue can occur with either shortage.
Don’t start B12 pills before testing. Supplements can make a later B12 blood test look normal, and they can mask a cause such as pernicious anemia that needs ongoing treatment. Ask for the tests first, then treat.
Alcohol and Liver Disease
Regular heavy drinking is one of the most frequent causes of large red cells in adults seen by family doctors. Alcohol acts on developing red cells directly, so MCV can be high even with normal B12 and folate, reaching as high as 120 fL in heavy drinkers.8PubMed. Macrocytosis as a consequence of alcohol abuse among patients in general practice In advanced liver scarring (cirrhosis), extra cholesterol builds up in the red cell’s outer membrane, making the cell larger.
The effect builds gradually, because only the red cells being made while you drink are affected, and new cells replace old ones over weeks. The raised MCV often comes with normal hemoglobin, so you feel fine and the flag may be the only sign. A doctor may weigh liver enzyme results and sometimes a low platelet count alongside the MCV, though none of these alone proves alcohol is the cause.
A glass of wine with dinner rarely explains a high MCV on its own. The effect is mainly seen with regular heavy intake, and the count usually settles once drinking drops.
Expect questions about your weekly drink count, not just whether you drink, and liver tests are often ordered alongside. Cutting back lets the next blood count show whether alcohol was the cause.9PubMed Central. Mean Corpuscular Volume Is Correlated with Liver Fibrosis Defined by Noninvasive Blood Biochemical Indices in Individuals with Metabolic Disorders Aged 60 Years or Older
Thyroid, Smoking, Medicines and Pregnancy
Lower thyroid hormone levels go along with higher MCV in US adults.10PubMed Central. Associations among thyroid hormone levels and mean corpuscular volume in adults in the US: A cross-sectional examination of the NHANES 2007–2012 dataset But anemia from an underactive thyroid is often normal-sized rather than large.11PubMed Central. Comparison of hematological parameters in untreated and treated subclinical hypothyroidism and primary hypothyroidism patients So thyroid is worth checking but isn’t the usual explanation for a markedly high MCV.
Testing is still reasonable. Thyroid function is checked with a simple blood test, usually thyroid stimulating hormone, so it is quick and cheap to rule in or out. Tiredness, feeling cold, weight gain, constipation and dry skin may point toward it, though many mild cases cause none. Replacement hormone often improves the blood count along with other symptoms.
Smokers have larger MCV and MCH values than non-smokers.12PubMed Central. Effect of Cigarette Smoking on Haematological Parameters in Healthy Population Smoke lowers oxygen and adds oxidative stress, which can disturb red cell DNA copying.13PubMed Central. Association between smoking status and complete blood cell parameters in baseline data from the Fasa adults cohort study The shift is small, around 3 fL higher on average.14Journal of Monno Medical College. Effect of Smoking on Red Blood Cell Parameters: A Cross-sectional Study in a Divisional City of Bangladesh Smoking can tip a borderline value over the line but rarely explains a big rise.
Drugs linked to large red cells include methotrexate, hydroxyurea, azathioprine, some HIV drugs, valproate, phenytoin, trimethoprim and chemotherapy.15TestWell. High MCV (Macrocytosis): Causes & What It Means | TestWell Mild cell enlargement is also common and normal in pregnancy, usually staying near the normal range.16StatPearls / Clinical Reference. What Causes High MCV and MCH in Blood Tests?
Bring every prescription to your appointment, including seizure drugs and arthritis treatments. Some drugs enlarge cells directly, others by lowering folate. Don’t stop a prescribed medicine on your own; ask whether the rise is expected. Your doctor may simply monitor rather than change anything.
Less Common Causes Worth Ruling Out
When the body destroys red cells faster than usual, the marrow releases more young red cells, which are larger than mature ones.17Cleveland Clinic Journal of Medicine. What evaluation should be done for an apparently healthy patient with an increased mean corpuscular volume (MCV)? A steadily high MCV can then point to a mild, well-compensated breakdown of red cells.18Cleveland Clinic Journal of Medicine. What evaluation should be done for an apparently healthy patient with an increased mean corpuscular volume (MCV)? When cell size has been high since childhood, an inherited red cell condition is more likely.19Cleveland Clinic Journal of Medicine. What evaluation should be done for an apparently healthy patient with an increased mean corpuscular volume (MCV)?
Myelodysplastic syndrome (MDS), a bone marrow disorder mostly of older adults, often produces large cells, sometimes above 106 fL and up to 140 fL.20PubMed Central. Acquired Myelodysplasia or Myelodysplastic Syndrome: Clearing the Fog Age 65 or over, a higher MCV and wider variation in cell sizes all make MDS more likely.21PubMed. Validation of a scoring system to establish the probability of myelodysplastic syndrome in patients with unexplained cytopenias or macrocytosis A young adult with an isolated, mildly high MCV is unlikely to have it.
The pattern across the whole blood count matters more than the MCV alone, because a high MCV with normal white cells and platelets is far more often benign. A mild, stable MCV that has barely changed across several tests over years is usually less concerning than one that keeps rising. Doctors also look at how much red cell sizes vary, since a wide spread alongside large cells can prompt closer inspection.
Some signals prompt a referral to a blood specialist: low white cells or platelets alongside large red cells, an MCV well above 110 fL without a vitamin shortage or alcohol, unexplained bruising, frequent infections or worsening fatigue, or no cause found after the first round of tests. A hematologist visit usually means repeat counts and a blood film examined under a microscope. A bone marrow sample is possible if marrow disease is suspected.
Could the Result Be a Lab Error
MCV can read falsely high when antibodies clump cells together or the sample has very high sugar.22PubMed. Spurious counts and spurious results on haematology analysers: a review. Part II: white blood cells, red blood cells, haemoglobin, red cell indices and reticulocytes An MCH that doesn’t match the other values is one clue the lab uses to spot an error.23PubMed. Spurious counts and spurious results on haematology analysers: a review. Part II: white blood cells, red blood cells, haemoglobin, red cell indices and reticulocytes If the result is a surprise, ask whether a repeat test makes sense.
Clumped cells can be counted as single larger ones, which pushes MCV upward. Very high glucose can make cells swell in the sample fluid, and a sample left standing for hours before testing can do the same. A repeat is reasonable for a single borderline value with everything else normal, for a sample that sat for hours before testing, or when diabetes was uncontrolled at the time of the draw.
Tests Your Doctor May Order Next
The first round usually includes B12, folate, liver tests, thyroid tests and a reticulocyte count. The reticulocyte count shows how fast the marrow is releasing young cells, which helps detect red cell breakdown.
A B12 blood level can look normal even when cells are short of B12.24SW Integrative Medicine. What Does It Mean If Your MCV Blood Test Is High? So doctors add methylmalonic acid (MMA) and homocysteine, which rise when B12 isn’t working inside cells.25PubMed. Etiology and diagnostic evaluation of macrocytosis The MMA test identifies true B12 shortage more reliably than the B12 level itself.26PubMed Central. Methylmalonic Acid and Homocysteine as Indicators of Vitamin B-12 Deficiency in Cancer Kidney problems can raise MMA, so results are read alongside kidney function.
Low B12 or a high MMA test points to B12 treatment and a search for why. Low folate often traces to diet or alcohol. If everything comes back normal, the plan may be watchful repeat testing.
For the follow-up visit, bring your medicine and supplement list, note your typical weekly alcohol, and mention diet changes like going vegan. Ask which results came back and what each one rules out.
How Long Until MCV Returns to Normal
Red cells circulate for about 120 days, so MCV won’t drop overnight.27Kantesti AI. What Causes High MCV and MCH in Blood Tests? After correcting B12 or folate, a measurable fall typically appears at 8 to 12 weeks.28Superpower. MCV Blood Test: Normal Range and High or Low MCV A repeat count before two months may look unchanged even if treatment is working.
Energy often improves within weeks, before MCV falls. After stopping alcohol, MCV also falls gradually over months. Nerve symptoms can take longer and may not fully recover. Hemoglobin, if it was low, often improves sooner than MCV does. Ask for a repeat count around three months. A value that is still rising prompts a new look for causes.
Why an Untreated B12 Cause Matters
Long-standing B12 shortage can damage the spinal cord, causing numbness, weakness and unsteady walking. This damage can occur even when MCV is only mildly raised or normal.29PubMed Central. Clinical features of different stage subacute combined degeneration of the spinal cord In one reported case linked to recreational nitrous oxide, MCV was 100 fL with normal hemoglobin and low B12.30Acta Neurologica Taiwanica. Subacute Combined Degeneration Caused by Nitrous Oxide Intoxication: Case Reports
Recreational “laughing gas” inactivates B12, and regular users can develop nerve damage quickly. Tell your doctor about any use.
Early signs are often tingling or numbness in the toes and fingers, which can be mistaken for something minor. Later signs may include unsteadiness, trouble with balance in the dark, weakness and changes in memory or mood.