Michael Smith, MD (Host): Welcome to Pediatrics in Practice, a CME podcast. I'm Dr. Mike. And with me is Dr. Sara McElroy, a pediatric hematologist and Director of the Stroke Program at Children's Mercy. Today, we're talking about how to recognize and manage abnormalities on the CBC in children, and when those findings should prompt a closer look or a referral to hematology. Dr. McElroy, welcome to the show.

Sara McElroy, MD: Thank you. Glad to be here.

Host: Abnormalities on CBCs happen all the time, both in kid world, adult world, you know, especially primary care. So, what are the most frequent findings you see referred that maybe could have been managed at the primary care level before a referral?

Sara McElroy, MD: Actually, I would say most things can be safely repeated prior to an immediate referral, and we'll probably discuss some exceptions to that later. But I do have a few situations in particular that I think are helpful for people to know. So if you see a decrease in any of the cell lines, so we're talking hemoglobin, neutrophil count from platelet count, in a child who has a mild viral or bacterial infection, so transient bone marrow suppression is really common during infection, particularly in kids. And those changes typically normalize within a few weeks after the infection has resolved. I would generally say most of those kind of mild decreases definitely can be repeated later on after the child is well. It doesn't necessarily warrant a referral to us.

A few other things. So, microcytic anemia, really common in kids, a lot of times it's due to iron deficiency. So, mild to moderate anemia, that is definitely from iron deficiency. The primary care provider can certainly manage that with oral iron supplementation and just repeating labs in a few months. Most kids respond really well to that. So, they don't always need to come and see us in hematology for that.

And then, I would also just encourage if a CBC was drawn kind of just as like a well check, that the child's otherwise well. And there were like really unexpected abnormalities on it, there is definitely lab error that can occur or lab artifact. So, I would encourage, particularly in a well-child, if something very unexpected comes up, that really the next step is just to repeat that CBC and make sure that those were actually true findings on that because we do see that not infrequently. So, those are just a few kind of things I would note.

Host: And I would assume too, how the patient is doing plays a role here, right? So, you have a young child, asymptomatic, and there's a slight change one of the CBC parameters, probably okay to go ahead and repeat and, you know, see how they're doing down the line. But you did mention there are some red flags, right? There are some things that probably need to go to a specialist like you right away. What are some of the red flags that you think we should refer right away to you?

Sara McElroy, MD: So, you know, I'm a hematologist, and the CBC can show you some things that are more oncology related. So, this is more oncology specific, but any report of a blast cell which is a very immature type of white blood cell on a CBC, is very concerning for leukemia. That should go straight to the ER probably, actually.

And then, a few other things. So, a neutrophil count that is in the severe range, so I would call that an absolute neutrophil count of less than five hundred in a child that's either actively febrile or just really ill-appearing that definitely should probably go to the emergency department as well.

And then, if we see pancytopenia, so all of the cell lines being low, so hemoglobin, platelets, and neutrophil count all being low, and if any of those are in the severe range or any combination of those in the severe range, then usually that would warrant either the ER or coming to hematology first. Sometimes providers can call us to get our advice on that.

And then, maybe just a few other things. So in a patient who has anemia and then also has jaundice, so scleral icterus or just kind of the yellow discoloration, that's concerning for a hemolytic process that can sometimes be more severe. So, I would say that would usually warrant coming to us pretty quickly.

I'll end this one with a severely low platelet count. So, let's say a platelet count of less than 50 in a patient who is having abnormal bruising or bleeding symptoms or petechiae, that kind of concerns me a little bit more and warrants coming either to us directly or, if it's really low and the bleeding symptoms are significant, maybe going to the emergency room.

Host: When you look at CBCs a lot in the primary care setting, isolated thrombocytopenia is something that is at least not uncommon and something that we have to deal with a lot. So, what clinical or laboratory clues help you to distinguish an isolated thrombocytopenia from benign, transient, or something more serious?

Sara McElroy, MD: Yeah. With thrombocytopenia specifically, it probably depends on how low it is. So if it's mild, rest of the CBC is normal, the child seems to be normal, not having any major symptoms, bleeding issues, I think that can be repeated. And a mildly low count like, you know, between 100,000 and 150,000 you probably don't need to repeat that anytime soon. Maybe at their next well-child check and just look at it there. If it's much lower than that, maybe warrants repeating a little bit sooner. But I always take into account what kind of symptoms the patient has.

And then, usually, we'll also get a little bit of history on the patient too, just like clinically how they're doing. Because sometimes a low platelet count could be a sign of something maybe genetic that's been going on for longer could progress, might warrant seeing us at some point. So, there are some symptoms and signs that we look for with that.

Host: I like what you said there where, you know, you're putting the symptoms together with the findings because I think sometimes as clinicians, we jump right to that data. We jump right to the labs. We look right at those numbers. And we have to remember how the patient feels is actually probably the most important thing and is going to drive how we interpret those labs, right?

Sara McElroy, MD: Absolutely, totally agree with that.

Host: But it's easy to forget that when you have all these numbers in front of you, right?

Sara McElroy, MD: Yeah. The CDC has so many numbers associated with it, but it can sometimes be overwhelming.

Host: I do want to talk about something that we see a lot too, so you're drawing a CBC and maybe the child has a viral infection, maybe an ear infection or something like that, or some sort of recent illness. How do you interpret the CBC and some maybe transient changes in the context of some of that stuff?

Sara McElroy, MD: Even before I'm interpreting that CBC, encourage people to maybe—unless there's a real clinical indication to obtain a CBC, not every child who has an infection, mild viral infection, bacterial, you know, ear infection probably doesn't need a CBC. But in the event that it's drawn and there's mild infection, the findings can be difficult to interpret. So, that's why I would say if you're seeing any changes in the setting of the child having some kind of infection, obviously, you have to talk with the family about what those look like. They might get a little stressed, a little nervous. But just reminding yourself, reminding the family that we see these transient changes, they do usually resolve within a few weeks. So, I usually recommend for providers to repeat them about four to six weeks after the child has gotten better.

And then, just giving the family good return precautions if you do see like a low neutrophil count saying, "Hey, you know, I think this will resolve soon. But if the child starts to develop symptoms that are unexpected, like prolonged fevers or looking really ill-appearing, then that would be the indication to go ahead and check those labs sooner rather than waiting.

Host: You know, infection always is interesting to me too because the basic idea, you get an infection, immune system activates, white count goes up. It also depends on where that patient is in the infection, what stage they're at that's going to determine what changes you see in white count, right? If the infection's just starting, you might not see any change.

Sara McElroy, MD: Correct. Yeah. You can see the white blood cell count be high, low, normal. All bets are off with kids and infections

Host: Medications, Dr. McElroy, are there any medications that affect the CBC we should be aware of?

Sara McElroy, MD: Yeah. There are a lot of medications that have adverse reactions that are related to CBCs. I'd say the most common would be there are some medications that can be used for certain psychiatric diagnoses that are very much known to cause a low platelet count or a low neutrophil count. A few of the antiepileptics can definitely be a culprit in thrombocytopenia or neutropenia. There's a lot more, but those are kind of the two that come to mind quickly. But definitely, if those are on board and you see those blood count changes, likely it is related to that.

Host: So, let me ask you this too. We talked a lot about referral, know those red flags, you know, when to make that immediate referral, even go to the ER. But if maybe the child is not emergently sick, but something's going on. You've repeated the CBC, you're still seeing that abnormality, and you're like, "Okay." Or the primary care doctor's like, "It's time to get this referral." Is there any other labs at that point that the primary care provider should order and have ready for you to look at? Or just send them over to you and you'll take care of all that?

Sara McElroy, MD: Yeah, I think there's some labs that they could get beforehand that's nice for us to know. Of course, you know, if there's any level of discomfort with that, then certainly they can put the referral into us. We're happy to see them do that. But a couple of notes. So, I always say that the CBC is not complete in a patient with anemia until they've had a reticulocyte count. And that doesn't come with a routine CBC. You do have to order that separately.

That reticulocyte count just tells you how well the patient's bone marrow is responding to them having a low hemoglobin. So if you see it being elevated, then there might be some kind of red blood cell loss or destructive process, whereas if that is low, then it's more of a production problem. So, I like to see that reticulocyte count. It's very helpful to me. Sometimes people will get a CBC and they won't get a differential, which is sometimes appropriate. But if a patient has a leukopenia, a low white blood cell count, then they definitely need to add on that differential so that we know which of the specific types of white blood cells is low, because that helps us out a lot as well. And then, I think, you know, if they have jaundice, of course, getting that hepatic function panel, looking at bilirubin is good to know.

I also like to see a peripheral smear. Not everyone's lab is going to do that, and that's okay. But if they have the opportunity to do a peripheral smear, that's really helpful for me to know what the pathologist is seeing actually under the microscope.

Host: So, what referral mistakes or misconceptions do you see most often?

Sara McElroy, MD: I think the one that comes to mind is where we get referrals for patients with abnormal blood counts, but it was done at a lab where they're using adult reference ranges, because pediatric reference ranges are going to be different than adults. And I just encourage providers to always, first of all, know what the reference ranges that are being used for the labs that they have drawn, and then making sure that they're comparing their patient's numbers to actual pediatric reference ranges. Because that can oftentimes save a referral to us and cost to the family and all that stuff, if we're making sure that we're using appropriate ranges.

And then, the differential, it will give you the percentages of the different white blood cells, and then will also give you absolute counts. And we really go off of absolute counts when we're determining whether something's high or low and not based off of that percentage. So, I see that occasionally where we will get referrals for a low percentage, but the absolute count is actually normal. That's a good thing to know too.

And then, my last thing, also related to white blood cells, we'll get referrals sometimes for leukopenia with the total white blood cell count being low. But then, when we actually look at the absolute counts of the neutrophils, the lymphocytes, they end up being normal, maybe on the low end of the range of normal for both of them. So, it makes the total look abnormal. But I'm not worried about that total if the actual, like, specific types of the cells are in the normal range, if that makes sense.

Host: That does make sense. And this has been fantastic information. Any last word for the listening audience about CBCs and referrals?

Sara McElroy, MD: We're always available for a phone call if it's something that you're not sure if it needs a referral, then that's what we're here for is to kind of help guide with that. We can let you know "Hey, this is actually not super worrisome. You can just repeat this," or "Yeah, we definitely want to see him." So, we are available for that if it comes up. But I think that's about it.

Host: Fantastic. I really want to say thank you for coming on. I know you're very busy. This was great information. I'm glad you found the time. For more information, you can go to cmkc.link/4yd2epd.

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