Diagnostics Decoded | Understanding Bilirubin
More Programs and Publications Featuring Dr. Kyle Riding
In this program:
What exactly is bilirubin? Medical laboratory scientist Dr. Kyle Riding explains how bilirubin is involved with red blood cells and waste products in the body and what the different bilirubin lab values mean.
Transcript
Interviewer:
So, Dr. Riding, tell us exactly what is bilirubin?
Dr. Kyle Riding:
I'm so glad you asked. Bilirubin is one of the most fascinating compounds that we routinely measure in the medical laboratory space. So to understand what bilirubin is, we have to think about red blood cells. We have to start with those beautiful red blood cells that carry oxygen for us throughout our body. Now, red blood cells carry a molecule called hemoglobin in them. And hemoglobin is this big protein-containing molecule that has this kind of smaller nitrogen-containing component to it. And when red blood cells die, sadly they do, every 120 days or so, that protein gets broken down, but we're left with that nitrogen-containing component. And our body needs to do something with it. It's now a waste product. And so what the body does is it takes that waste product, it's called heme. So heme is one component of hemoglobin. And that heme gets converted first to a substance called biliverdin, which rapidly gets made into bilirubin.
Okay? That's what we're talking about right now, is the beautiful bilirubin. And when that bilirubin is first created, it actually is, it's not able to be excreted out of the body all that readily as a waste product. It is too fat-soluble, and our body likes to get rid of things that are water-soluble, mainly through our urine. Okay? So what happens is, is this unaffected, unprocessed, what we call unconjugated bilirubin gets released into circulation, binds to a protein called albumin, and albumin is kind of like the school bus of our blood, carries things all throughout our circulatory system, and it goes to the liver. And in the liver, the liver does this fancy chemical process called conjugation. Basically, we add a new organic molecule or organic component to the unconjugated bilirubin to turn it into conjugated bilirubin. And that conjugated bilirubin is far more water-soluble, which means the body can excrete it far more readily. And it's a waste product. We want to excrete it. We want to get rid of it after all. We don't like waste building up in our body.
So what then happens is the conjugated bilirubin goes into our bile ducts and is the main component of our bile. And so, actually, that's kind of where they get their name from. The bilirubin builds the bile. The bile then gets released into your intestines, gets kind of consumed and eaten by the bacteria in your gut. And when you go to the bathroom and not to urinate, you do get rid of the bilirubin. And, in fact, that processed bilirubin that your intestinal bacteria have kind of eaten up and converted, well, that's what gives your fecal matter its color. And I want to make sure if anyone is eating their dinner or their lunch right now, I don't get into too much more detail beyond that. So we have that unconjugated bilirubin that is released right after a red cell dies, it gets carried to the liver and gets converted to conjugated bilirubin and then is excreted out through the bile ducts. And then some of it's excreted through the intestines, through our fecal matter, some of it is reabsorbed and excreted out of our kidneys in our urine. But I want to throw two more terms at you, because this is going to be important.
We often don't call it conjugated bilirubin or unconjugated bilirubin on lab reports. We call it direct and indirect on lab reports. And the direct term and the indirect term just means, can we measure it directly in a lab, or are we indirectly measuring it through a calculation? So the water-soluble form, that conjugated bilirubin, guess what? We can measure that very rapidly, very easily. And so we call that direct bilirubin. Unconjugated bilirubin is trickier to measure, and so that's called indirect bilirubin. And when we measure all of it together, which we're able to do, we get total bilirubin. And so by looking at not just total bilirubin being elevated, but which two of those fragments of the total bilirubin is elevated, helps the clinician appreciate what's going on inside of the patient.
Interviewer:
So should patients also have to pay attention to indirect versus direct bilirubin as to just the total? Because, at least from my experience, clinicians have always explained just the total to me.
Dr. Kyle Riding:
So it's always good for a consumer or a patient of healthcare to be knowing what's going on with their labs. Typically, the provider will first notice that total bilirubin, and as part of their diagnostic process, they're going to look at the direct versus the indirect. The patient is going to have it explained as if it's kind of, usually just for simplicity sake and for the sake of time, it's going to be spoken about as total bilirubin. But a patient should feel comfortable looking at, my total bilirubin is elevated, is that elevation mainly from direct bilirubin or indirect bilirubin? And what's going to happen is, if it's because of direct bilirubin, we're thinking more liver. That's what we're thinking or gallbladder or bile duct. If it's more indirect that's elevated, well, guess what? We're now thinking more hemolytic anemia, we're something where red cells are dying too quickly. One more tip, a lot of lab reports won't necessarily include the indirect bilirubin result. It will just have the total and the direct. But here's the great thing. To get your indirect, take your total, subtract your direct, and there's your indirect. So even if we in the lab aren't putting it on the report, you as the patient can quickly calculate it to help make you feel empowered and informed about what's going on.
I love this question, and I could probably spend an hour talking about this, but I'll spare you on that. There are so many different things that policymakers and community leaders could be doing to try and limit the inequities that are happening. When we think about the inequities that are going on and…when it comes to diabetes. We're really talking about folks at lower socioeconomic status in many cases. We're talking about folks with lower educational attainment in many cases. And, unfortunately, we're talking about individuals who may not be white. And we know in the United States that in many cases, those things can sometimes, unfortunately, be blended together because of history. So in terms of what policymakers can do, I would say, number one, let's get rid of food deserts. Because if you...
Interviewer:
Yes.
Dr. Kyle Riding:
[chuckle] If you look at lower income communities, it is so hard to find healthy food. You'll find McDonald's, which I'm not.. I like myself a McDonald's or Burger King every once in a while. But you won't find healthy produce. You won't find healthy meats to be able to eat if you enjoy a carnivorous lifestyle like I do. And so food deserts are really a policy level thing that we can address as a community.
The other thing is creating safe outdoor spaces where folks can get outside and be physically active, or safe indoor spaces that are meant to drive physical activity. I remember growing up, I grew up in a city, it was not really...my parents would say, "Do not go further than the sidewalk in front of the house." Because there was a busy street in front of us, and there were busy streets around us, and people drove like maniacs. It wasn't safe for my sister or I as kids to be outside playing much further than that sidewalk because we had risks of being, unfortunately, hit by a car.
When we moved into the town next door, which was of a higher socioeconomic status, they had walking trails, a bike path, they had a fitness center that was free for residents, and guess what? I was a heavy kid, I wore the...embarrassing enough. But when we moved to that town that had better access to physical activity, my weight changed, I went down, I was living a healthier lifestyle, and all of those things matter. So I would say those are two major things that policymakers would be able to address that can make a difference.
Interviewer:
And I was an inner city kid growing up in Boston and one of the worst parts of Boston, and there were parks, but we just were not advised to go to them [chuckle] because there was logging activity and things like that. So, yeah. There's a lot of things that need to change, and especially the food deserts are a major thing that force people to eat unhealthy foods without them having a choice too.
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