Lab Values, part 18: Hemoglobin (Hgb) & Hematocrit (Hct)

Hi, I'm Meris. And in this video, I'm going to be talking to you about the lab values hemoglobin and hematocrit. Let's go ahead and get started. So first up, let's chat about hemoglobin. Hemoglobin is an incredibly important component of the red blood cell. It is the actual molecule that is responsible for carrying both oxygen and carbon dioxide around in the blood. So it is the portion of the red blood cell that does the gas carrying. So it's super important because even if I have enough red blood cells, if I don't have enough hemoglobin, I can't carry around those molecules because there's not enough carriers to cart them around, right?

So in this case, we, again, see the expected range being broken down based on the sex assigned at birth. This, again, has to do with the oxygen demands that our bodies have based on their unique composition. So if I have more muscle mass than fat tissue, I'm going to need way more oxygen to supply those muscles. So if you are assigned female at birth, the hemoglobin range is going to be 12 to 16 grams per deciliter. And again, remember, that's a pretty big range, but there's room for different physiologic processes going on there, right, because if I'm having a menstrual period, then I'm going to expect that I'm going to have a little blood loss, right? I'm going to have a little bit decreased hemoglobin. For patients assigned male at birth, it's going to be slightly higher due to that increased muscle mass and oxygen demand. Because of that, we're looking at 14 to 18 grams per deciliter.

Now, what about hematocrit? Hematocrit, this one stumps people a lot, and it's because we're not measuring a substance. There's not a thing floating around in my blood called hematocrit. Hematocrit is actually looking at the ratio between how much stuff is in my blood and how much liquid is making it up. So this is really looking at, what is the percentage of my blood that is red blood cells? It's looking at that ratio of cells to everything else. So when we think about this, we, in general-- again, this is going to be separated based on sex lines, but for patients assigned female at birth, it's going to be 37 to 47 percent of their blood. That's their hematocrit. That's how much of their blood should be red blood cells. And for patients assigned male at birth, it's going to be 42 to 52 percent. So again, a little bit more for a patient assigned male at birth because they have a higher muscle mass, and it's going to have more oxygen demands associated with it.

Now, what are some possible causes of disturbances here? So if we're talking about lower levels in both hemoglobin and hematocrit, because again, these two typically are referred together, we sometimes will even call these H and H, hemoglobin and hematocrit. You can run them together as just an H and H because sometimes I really only care about that. If you come into my ER, and you're complaining of some different things, we run some lab tests and I find out, "Uh-oh, my patient is bleeding," well, then this becomes something we need to pay attention to. If this is a slow, small bleed or we think it's resolved, we need to see what's going on with the hemoglobin and hematocrit, the H and H. I don't need to count every single cell. Again, I just want to count these a couple of hours in the future, and then a couple of hours after that, so on and so forth. I'm not trying to waste everybody's time, energy, and money by counting the white blood cells and the platelets and looking at the morphology of everything and all of the other stuff that goes into a complete blood cell count, right? I just want to run it as an H and H. I just want to pay attention to these. It's going to save my patient money, and it's going to save time for the laboratory technician as well.

So possible causes of lower levels. Well, I already told you one of them. It's going to be bleeding. If my patient is bleeding, they are going to be losing hemoglobin, and hematocrit will be changing drastically. I need to be concerned here, right? Anemia also, especially related to iron deficiency anemia. If I don't have enough iron, which is the primary molecule in hemoglobin-- I need four atoms of iron to make up a molecule of hemoglobin. So if I don't have enough iron, then I have iron deficiency anemia because I can't make hemoglobin without it. So again, I can't carry anything without those molecules. And then also, kidney disease. Remember I told you in a previous video that your kidneys produce a chemical called erythropoietin. In response to low blood oxygen, low blood flow to the kidneys, they're going to say, "Hey, I need some more red blood cells." More red blood cells come along with more hemoglobin. So we will see that those will be low in somebody who has kidney disease.

Now, what about elevated levels? What if my patient has elevated levels of hemoglobin and/or hematocrit? In this case, causes could include chronic hypoxia, such as COPD. If I am chronically hypoxic, I'm going to be asking my kidneys to make more EPO all the time. They're going to be carrying around more hemoglobin with the hopes of increasing the amount of oxygen that's available due to the fact that I can't do anything with it because of my COPD. They're going to try and make more oxygen available. This is also why you will see patients who are routine cigarette smokers will also have elevated hemoglobin due to that chronic hypoxia, even if they haven't yet reached the stage of COPD. Polycythemia. If I have too many cells in my blood, then that's going to also affect my hemoglobin and the percentage of that hematocrit.

Hypovolemic shock. If I am not hemorrhaging-- and hemorrhage is a type of hypovolemic shock, but in this case, I'm talking about hypovolemic shock that is solely related to fluid volume loss, not blood loss. And let me give you an example. Somebody who is incredibly dehydrated, they have not taken in enough fluid, or maybe someone with excess losses such as NG tube suctioning, vomiting, diarrhea, profuse sweating, etc. Either way, either I have too little in or too much out, but the result here is that I have less plasma. If I have less plasma, do I have more red blood cells and more hemoglobin? No, but it looks like I do because it's more concentrated of a sample. And then if I have less plasma, do my red blood cells make up a portion of my blood that is greater than usual? Yes. There's not enough plasma to offset that balance. That's going to lead to higher levels as well. Severe dehydration should go in your differential. If you see somebody with those elevated H and H levels, you need to be thinking, "This patient could be having severe fluid deficit," or, "Is this somebody who has that chronic hypoxia due to something like cigarette smoking, COPD, etc?"

All right. I'm so glad you stayed until the end because I'm going to test your knowledge of key facts I provided in this video with some quiz questions.

The nurse educates a patient that which lab value is reported as a percentage, as it is the percentage of the blood made up by red blood cells?

Hematocrit.

A patient looking to increase their hemoglobin level should be educated to increase their dietary intake of which mineral?

Iron.

All right. That is it for this video. I do hope you learned something. Thanks so much, and happy studying.