Unlocking The Puzzle of Your Low MCV Blood Test

Are you looking at some of your lab tests and wondering why your MCV blood test is low? In this video, we're going to look at just that. We're going to explore what it means when that is low, what causes it, and alternative reference ranges to consider.
In the case of a low MCV level, it usually has to do with low hemoglobin and low iron. In this video, we're going to talk about the details surrounding low MCV blood tests that really matter.

A low mean corpuscular volume or low MCV on a blood test indicates that the average size of your red blood cells is smaller than normal. So, the MCV is one of the parameters measured in a CBC blood test, and it's expressed in femtoliters or FLs. Measurement is useful in diagnosing and understanding various medical conditions, and the typical reference range for the MCV is going to be from 80 to around 100 or maybe 97.

This reference range can vary from one lab to the next. So if the MCV falls on the low end of the reference range or below the reference range, your cells are considered to be microcytic, meaning very small. And if it goes above the upper end, it's macrocytic. We typically start to consider someone's cells too low or maybe approaching a problem of microcytic when levels are in the low 80s, say 83 or less.

So if this is happening to you, what does it actually mean when those cells are on the smaller side or when your MCV is on the low side or microcytic side? Really, what we're asking is why are they so small to begin with? So overall, in our body's ability to produce hemoglobin in an efficient way, decreases. The overall size of the cells is going to shrink. And that's because hemoglobin is the major protein that makes up the red blood cell. So when you can't make hemoglobin for various reasons, the size of the cells is going to go down.

So let's look at some of the reasons why, some of the various diagnoses and reasons behind why hemoglobin production can be affected, leading to low MCV. First and most common is going to be iron deficiency anemia. So one of the most common causes for low MCV is from iron deficiency. Now you don't actually have to have anemia to have iron deficiency. So when you start to see your MCV on the lower end of normal, that's a good clue that you should be looking for deficiency.

And you can do that by running a serum iron test, total iron binding capacity, and ferritin. Just because you have a low MCV doesn't mean it's because of iron deficiency, as we'll see. There are other reasons, and it's important to figure that out because you do want to resolve it if possible, but there are other more chronic reasons that that can happen which we'll get into here in a sec.

In the case of iron deficiency, the cells are smaller in size because you need iron to make the hemoglobin, as we said, hemoglobin is a fundamental aspect of the red blood cells. So when you don't have that, the cells are going to be smaller. Chronic inflammation and chronic disease states like rheumatoid arthritis, kidney disease, inflammatory bowel disease, and just overall inflammation in general can lead to something called anemia of chronic disease.

And this is where the body's ability to utilize iron is impaired. The inflammation is basically triggering the body to take some of that iron and store it away, keeping the rest of the body protected because iron can sometimes increase inflammation. And because there's already so much inflammation going on, the body wants to hold that back. And that can lead to smaller red blood cells because it's going to impair the production of hemoglobin once again. The third reason for low MCV blood tests or microcytic cells is thalassemia. Thalassemia is a genetic disorder affecting the hemoglobin production. Because hemoglobin production is impaired, it results in smaller, more fragile red blood cells leading to low MCV.

Lead poisoning. So lead can also interfere with hemoglobin production, leading to decreased size of those red blood cells that you're pushing out. Now, of course, lead can cause all kinds of other problems. And just because you have low MCV doesn't mean you have lead poisoning. But if you've ruled out some of these other reasons and you still have persistently low MCV, then that might be something to look at.

There are certain medications that can also interfere with hemoglobin production and lead to some smaller than normal red blood cells, some chemotherapy medications like methotrexate and 5-fluorouracil, and some antiretroviral medications as well used to treat viral infections. And the last one that I'll talk about is sideroblastic anemia. This is a pretty rare type of anemia where the body has difficulty incorporating the iron into the hemoglobin, and this also can lead to low MCV.

So what does it mean when you have low MCV blood tests? Well, basically, it means that your red blood cell size is small, and you may have difficulty making hemoglobin, and there are various reasons that can happen.