Frequently Asked Questions

MCV stands for Mean Corpuscular Volume (also called Mean Cell Volume). It is a measurement included in every Complete Blood Count (CBC) panel that calculates the average size and volume of your red blood cells (erythrocytes) in femtolitres (fL).

Red blood cells carry oxygen from your lungs to every cell in your body. Their size matters — cells that are too small cannot carry enough hemoglobin (oxygen), while cells that are too large may indicate problems with DNA synthesis in the bone marrow. MCV is the primary tool doctors use to classify the type of anemia you may have and identify its underlying cause.

Your MCV result tells your doctor how big or small your red blood cells are on average. The normal reference range is 80 to 100 fL. Here is what the three possible outcomes mean:

• Low MCV (below 80 fL) — Your red blood cells are smaller than normal. This is called microcytic anemia. Most common causes: iron deficiency, thalassemia, chronic disease anemia.
• Normal MCV (80–100 fL) — Healthy red blood cell size. However, a normal MCV does not completely rule out disease — combined deficiencies can mask each other.
• High MCV (above 100 fL) — Your red blood cells are enlarged. This is called macrocytic anemia. Most common causes: B12 deficiency, folic acid deficiency, hypothyroidism, liver disease, alcohol use.

The universally accepted normal MCV range is 80 to 100 femtolitres (fL). This range applies to both men and women in most standard laboratory reference guides.

• Severely Low MCV: Below 70 fL — urgent investigation needed
• Low MCV: 70–79 fL — microcytic anemia likely
• Normal MCV: 80–100 fL — healthy red blood cell size
• High MCV: 101–115 fL — macrocytic anemia
• Severely High MCV: Above 115 fL — urgent clinical evaluation

Note: reference ranges can vary slightly between laboratories. At MCV Blood Test Houston, we use the internationally standardised 80–100 fL threshold.

A low MCV (below 80 fL) means your red blood cells are smaller than normal — a condition called microcytic anemia. Small red blood cells often cannot carry enough hemoglobin and oxygen to meet your body's needs.

The most common causes of low MCV include:

• Iron deficiency anemia — the #1 cause worldwide, often from poor diet, heavy periods, or gastrointestinal blood loss
• Thalassemia — a genetic blood disorder causing small, fragile red blood cells
• Anemia of chronic disease — from long-term inflammatory conditions
• Lead poisoning — especially in children
• Sideroblastic anemia — iron is present but cannot be properly used

A high MCV (above 100 fL) means your red blood cells are larger than normal — called macrocytosis or macrocytic anemia. Enlarged red blood cells are often fragile, have a shorter lifespan, and may not function efficiently.

Common causes of high MCV include:

• Vitamin B12 deficiency — very common in vegetarians, vegans, and elderly patients
• Folic acid (B9) deficiency — especially during pregnancy
• Hypothyroidism — underactive thyroid slows red blood cell production
• Liver disease and alcoholism — alcohol directly enlarges red blood cells
• Medications — methotrexate, AZT/zidovudine, hydroxyurea, phenytoin
• Bone marrow disorders — aplastic anemia, myelodysplastic syndrome

Both MCV and MCH are part of the CBC (Complete Blood Count) panel and together help classify anemia — but they measure different things:

• MCV (Mean Corpuscular Volume) — measures the average size (volume) of red blood cells in femtolitres (fL). Normal: 80–100 fL.
• MCH (Mean Corpuscular Hemoglobin) — measures the average amount of hemoglobin contained in each red blood cell in picograms (pg). Normal: 27–33 pg.

In practice, MCV and MCH tend to move together. Low MCV usually comes with low MCH (iron deficiency). High MCV usually comes with high MCH (B12/folate deficiency). When they diverge, it points to more complex conditions like thalassemia or mixed deficiency states.

The MCV blood test is performed to measure the average size of your red blood cells and is automatically included in every CBC (Complete Blood Count) panel. Doctors use MCV to:

• Diagnose and classify different types of anemia
• Identify vitamin B12, folic acid, or iron deficiencies
• Detect genetic conditions like thalassemia
• Monitor the effects of cancer treatment (chemotherapy/radiotherapy)
• Assess liver disease severity and alcohol-related damage
• Screen for thyroid disorders
• Evaluate overall bone marrow function

MCV is often the first clue that a patient has a nutritional deficiency or blood disorder, even before symptoms become obvious.

Low MCV means your red blood cells cannot carry enough oxygen, which affects nearly every organ. Common symptoms of low MCV / microcytic anemia include:

• Persistent fatigue and weakness that doesn't improve with rest
• Pale or yellowish skin, pale inner eyelids or gums
• Shortness of breath on mild exertion
• Dizziness and lightheadedness
• Rapid heartbeat (palpitations)
• Frequent headaches
• Cold hands and feet
• Brittle nails and hair loss
• Unusual food cravings (eating ice, dirt — called pica)

High MCV is most commonly caused by B12 or folate deficiency, which affects not just blood cells but the nervous system too. Symptoms include:

• Fatigue, weakness, loss of energy
• Loss of appetite and unintentional weight loss
• Tingling or numbness in hands and feet (nerve damage from B12 deficiency)
• Memory problems, poor concentration, brain fog
• Diarrhea or constipation
• Sore, inflamed, or swollen tongue (glossitis)
• Mood changes — depression or irritability
• Palpitations and shortness of breath

If you experience neurological symptoms (tingling, memory loss) alongside fatigue, get your MCV and B12 levels tested immediately at MCV Blood Test Houston — call 340-348-2786.

MCV is calculated automatically by modern hematology analyzers using this formula:

MCV (fL) = (Hematocrit % ÷ RBC count in millions/μL) × 10

For example: If your hematocrit is 42% and RBC count is 5.0 million/μL → MCV = (42 ÷ 5.0) × 10 = 84 fL (normal range).

In modern automated hematology analyzers, MCV is measured directly using electrical impedance (Coulter principle) or laser diffraction, making it highly accurate. Results are reported in femtolitres (fL), where 1 fL = one quadrillionth of a litre.

No fasting is required for the MCV blood test alone. You can eat and drink normally before having blood drawn for an MCV or CBC test.

However, there are a few important preparation tips to ensure the most accurate results:

• Avoid alcohol for 24–48 hours before the test — alcohol directly enlarges red blood cells and can falsely elevate your MCV value
• Stay well hydrated — drink adequate water before your appointment
• Disclose all medications — especially methotrexate, AZT, phenytoin, or chemotherapy drugs, as these affect MCV
• If MCV is ordered as part of a broader CMP or fasting glucose panel, then 8–12 hours of fasting may be required for those additional tests

At MCV Blood Test Houston (6565 Fannin St, TX 77030), your MCV blood test and CBC results are typically available within 4 to 24 hours of sample collection.

• Same-day results available for urgent or priority cases
• Results are delivered via secure email, SMS notification, and online portal
• Printed hard copy available at the Houston lab
• For add-on tests (B12, ferritin, folate), results may take 24–48 hours depending on processing

Call us at 340-348-2786 or email mcvbloodtest@gmail.com to book and confirm your turnaround time preference.

Yes — a normal MCV does not completely rule out anemia. This is one of the most important clinical points about MCV interpretation.

A condition called "dimorphic anemia" occurs when a patient has both iron deficiency (which lowers MCV) and B12/folate deficiency (which raises MCV) at the same time. These opposing effects cancel each other out, producing a falsely normal MCV despite significant anemia. This is why MCV must always be interpreted alongside:

• Hemoglobin and RBC count
• RDW (Red Cell Distribution Width)
• Serum ferritin and iron studies
• Vitamin B12 and folic acid levels
• Reticulocyte count

MCV and RDW are both part of the CBC and measure red blood cell characteristics — but in completely different ways:

• MCV measures the average size of all red blood cells. It tells you whether cells are small, normal, or large on average.
• RDW (Red Cell Distribution Width) measures the variation in size between red blood cells. A high RDW means cells vary widely in size (some big, some small).

The combination of MCV and RDW together is the most powerful tool for differentiating iron deficiency anemia from thalassemia trait: Low MCV + High RDW = Iron Deficiency Anemia / Low MCV + Normal RDW = Thalassemia Trait. This distinction is critical because the treatment for each is completely different.

Yes — alcohol is one of the most direct causes of elevated MCV. Alcohol has a direct toxic effect on the bone marrow and red blood cell membranes, causing red blood cells to enlarge (macrocytosis) independent of any vitamin deficiency.

Even moderate or social drinking over time can raise MCV above the normal range. In patients with chronic alcohol use disorder, MCV above 100–105 fL is very commonly seen. Importantly:

• Alcohol-related MCV elevation can occur even with normal B12 and folate levels
• MCV normalises slowly (over 2–4 months) after stopping alcohol consumption
• Alcohol also impairs folate absorption, compounding the macrocytosis effect
• Elevated MCV in someone who drinks is a useful indirect marker of alcohol misuse

Avoid alcohol for at least 24–48 hours before your MCV blood test for the most accurate results.

Pregnancy significantly affects blood composition and can influence MCV values in several ways:

• Blood volume expansion: Plasma volume increases by 40–50% during pregnancy, which can dilute the blood and slightly lower apparent MCV and hemoglobin — this is called physiological (dilutional) anemia of pregnancy.
• Increased folic acid demand: The growing fetus requires large amounts of folate for neural tube development. Folic acid deficiency during pregnancy directly raises MCV (macrocytic anemia). Supplementation with 400–800 mcg/day folic acid is critical from conception through the first trimester.
• Iron demands: Iron deficiency is very common in pregnancy and lowers MCV. Routine CBC and MCV testing at each trimester is recommended for all pregnant women.

Testing frequency depends on your health status and risk factors:

• Healthy adults (no known conditions): Once per year as part of a routine annual CBC health check
• Known iron deficiency, B12, or folate deficiency: Every 3–6 months to monitor treatment response
• Patients on chemotherapy or medications affecting blood counts: Every 1–3 months as directed by your oncologist or physician
• Chronic disease patients (CKD, liver disease, thyroid disorders): Every 3–6 months
• Pregnant women: Each trimester (3 times during pregnancy)
• Vegetarians and vegans: Annually at minimum, every 6 months if B12 supplementation is not reliable

Yes — several commonly prescribed medications can raise MCV by interfering with DNA synthesis in red blood cell precursors in the bone marrow, causing macrocytosis:

• Methotrexate — used for rheumatoid arthritis, psoriasis, and cancers
• AZT / Zidovudine — HIV antiretroviral medication (very common cause)
• Hydroxyurea — used for sickle cell disease and certain leukemias
• Phenytoin / Valproate — anticonvulsant medications reduce folate absorption
• Trimethoprim — antibiotic that blocks folate metabolism
• Colchicine — used for gout
• Proton pump inhibitors — long-term use reduces B12 absorption

Always disclose all current medications to your MCV Blood Test lab team before testing.

Yes — in most cases, MCV can return to normal with proper treatment once the underlying cause is identified and addressed:

• Iron deficiency anemia: MCV typically normalises within 4–8 weeks of starting iron supplementation or treating the source of blood loss. Reticulocyte count rises within 1–2 weeks as a sign of recovery.
• B12 or folate deficiency: MCV begins to fall toward normal within 2–4 weeks of supplementation (oral or injections). Full normalisation may take 2–3 months.
• Alcohol-related macrocytosis: MCV normalises slowly — over 2–4 months after stopping alcohol completely.
• Thalassemia: MCV will not normalise as this is a genetic condition — but treatment focuses on managing symptoms and preventing complications.

Regular MCV Blood Test monitoring during treatment confirms your progress. Book a follow-up at our Houston lab: 340-348-2786.

Yes! MCV Blood Test offers free home sample collection across Houston, TX and surrounding areas. Our certified phlebotomists come to your home or office at your preferred time, draw your blood, and have your results back to you within 24 hours.

• Available areas: Houston, Sugar Land, Pearland, Katy, Pasadena, The Woodlands, Missouri City
• Collection hours: 6:00 AM – 10:00 AM daily (early morning slots preferred for best sample quality)
• Lab address: 6565 Fannin St, Houston, TX 77030 (Texas Medical Center)
• Book by phone: 340-348-2786
• Book by email: mcvbloodtest@gmail.com