Lab Values That Help Decipher Bilirubin and Hemolysis Issues
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In this program:
What are laboratory values that help determine issues with bilirubin and hemolysis? Dr. Kyle Riding explains lab tests involved with bilirubin values, components of complete blood counts, and differences between ALT and AST tests.
Transcript
Deandre White:
Are there other lab values that can help the provider inch towards this is a direct issue, or this is an indirect issue? You mentioned liver enzymes, but what about for hemolytic issues as well?
Dr. Kyle Riding:
Sure. So when we're thinking about bilirubin, it is often ordered along as part of a liver function test, LFTs. And so we have our total bilirubin, our direct and indirect bilirubin, and then we have usually three enzymes, ALT, AST, and ALP or alkaline phosphatase. Because we love acronyms in medicine, we just have to make everything an acronym to confuse everybody. I don't know why we do it, but hey, it makes for good Grey's Anatomy quick little episodes when you hear them shouting out, give me a CBC and a chem 7. But here's the thing, when we have a hemolytic process, indirect bilirubin will be elevated and cause the total bilirubin to go up. Additionally, what we might see on that liver function test panel, depending on the type of hemolytic anemia, what we might see is an elevation in the AST, AS as in snake T. I'm not a big snake fan, but better to say it that way. Because AST is found in red cells at a pretty high level. So when those red cells rupture, the AST gets released along with the unconjugated bilirubin that's going to form because of that rupturing. That doesn't happen in every single type of hemolytic anemia. There's different mechanisms, but it is possible.
Conversely, if it's something related to the liver, we're going to see the direct elevated and typically we'll also see the ALT be more elevated. Because I always remind my students and whenever I talk to patients, I tell them, think ALT, think the L means liver. It has a really good specificity for the liver. It's not the only place in the body we find ALT, but the liver is a major source of that enzyme. So when we see injury happening to the cells in our liver, we often see ALT be the enzyme that is most elevated because it gets released as the damage happens to those cells. Now, if it's something going on with the bile ducts, where there's a blockage, typically, again, when you think bile ducts, it's right next to the liver, they're right attached to each other. But what will happen is we'll see the direct elevation or the direct bilirubin be elevated, and we'll typically see that ALP or alkaline phosphatase be elevated. How I think of that, I have a cheesy little way of remembering this. ALP, the P could be a plug in the bile ducts. It could be a little blockage in the bile ducts.
Just a fair warning, though, like the other two enzymes, ALP is found in other cells of the body. So it's important to recognize bile duct blockages or injury is not the only place you'll see elevated ALP. It's important to look at everything holistically on these panels, use that bilirubin to kind of identify if there is a potential liver issue before just diving right into the enzymes. This is why physicians are so highly trained as the intricacies of our body is so important for them to understand to treat us effectively. But I hope that provides some details, so those watching this appreciate what's going on, what the physician is looking at, and the importance of looking at everything together and not just one lab result in a silo.
Deandre White:
Yes, I like how you describe the differences between AST and ALT, because I feel like those are often kind of just interchanged. And either you see one elevated or both are elevated, and you don't really know why there's a difference between the two and that they're both amino acids, and it all just kind of seems to be the same thing even though it's really not. But to kind of touch a little bit more on the hemolytic side if we're seeing this might be a hemolytic issue and we're seeing indirect being elevated for bilirubin, are there any values on a CBC panel that would help a provider? Because we have talked about the elevations on a hepatic panel, but what about on a CBC panel that can help them inch towards getting a better idea if there's hemolysis for the patient?
Dr. Kyle Riding:
Absolutely. So with the complete blood count, we have our white blood cells, we have our red blood cells, and we have our platelets, and so yes. In fact, the hemolytic anemia, the anemia is going to be defined by a reduction of the hemoglobin on the CBC. So for an anemic process to...anemic process being present, it's defined by the hemoglobin being low on that CBC. Additionally, typically, depending, again, on the cause, we may often see the red blood cell count go down as well, if the red cells are rupturing and the bone marrow can't keep up with that loss. Additionally, if it's an infectious cause, if there's some type of infection causing the hemolytic anemia, then we may see elevations in our white blood cells as well. So absolutely, that complete blood count, the CBC, can give some really important information to the provider when they see that indirect bilirubin be elevated. Because it is important to call back on the fact that while hemolytic anemias are the most, kind of most common cause of an increase in indirect bilirubin, there are some other causes as well, and so that CBC is going to give the final look to the provider of, "Hey, is this really an anemic process, or is there something else going on?"
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