MCV Blood Test: What a Low or High MCV Means

Most people reach this page holding a report with MCV flagged low, and the honest answer is that low MCV has two very different common causes in Pakistan.

MedlinePlus explains that red blood cell indices are part of the complete blood count and are usually used to help diagnose the cause of anaemia, a condition in which there are too few red blood cells. On a low MCV it states: MCV below normal means microcytic anaemia, which may be due to low iron levels, lead poisoning, or thalassemia.

Those last two words change what happens next. Iron deficiency is treated with iron. Thalassemia trait is inherited, is not fixed by iron, and matters for whom you marry and the children you have. Taking iron for months without a diagnosis is the mistake this page exists to prevent.

If your MCV is low, ask your doctor whether you need ferritin, an Hb electrophoresis, or both. In a country where thalassemia trait is common, a low MCV with normal iron stores is a reason to test for thalassemia rather than to buy more iron syrup.

MedlinePlus lists them.

• MCV, the average red blood cell size, called mean cell volume
• MCH, the haemoglobin amount per red blood cell, called mean cell haemoglobin. We have a separate page on [MCH](/labs/tests/mch-blood-test)
• MCHC, the amount of haemoglobin relative to the size of the cell, called mean cell haemoglobin concentration

It explains that haemoglobin transports oxygen, that red cells carry haemoglobin and oxygen to your body's cells, and that the indices measure the size and haemoglobin of those cells so the results can be used to diagnose different types of anaemia.

MedlinePlus gives these as the normal range.

• MCV: 79 to 95 femtolitres
• MCH: 26 to 33 picograms per cell for females, 27 to 33 picograms per cell for males
• MCHC: 32 to 36 grams of haemoglobin per decilitre

It adds that these are common measurements, that normal value ranges may vary slightly among different labs, that some labs use different measurements or may test different samples, and that you should talk to your provider about the meaning of your specific results.

Read the range printed on your own report, not one from the internet. A value one point outside a range is a very different thing from a value far outside it.

MedlinePlus maps the three outcomes.

MCV below normal, microcytic anaemia. May be due to low iron levels, lead poisoning, or thalassemia.

MCV normal, normocytic anaemia. May be due to sudden blood loss, long-term diseases, kidney failure, aplastic anaemia, or human-made heart valves.

MCV above normal, macrocytic anaemia. May be due to low folate or vitamin B12 levels, or chemotherapy, or liver disease.

That last one is useful and under-recognised. A high MCV in someone who is tired is a reason to check [vitamin B12](/labs/tests/vitamin-b12-test-price) and folate, not a reason to take iron. Iron is the reflex in this country, and in macrocytic anaemia it is the wrong reflex.

MedlinePlus states that no special preparation is necessary. No fasting.

A blood sample is taken from a vein in your arm. MedlinePlus notes that when the needle is inserted some people feel moderate pain while others feel only a prick or stinging, and that afterwards there may be some throbbing or a slight bruise which soon goes away. In Lahore the sample can be collected at your home at no extra cost.