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When Should You Repeat a Child's CBC? · Pediatrics in Practice: A CME Podcast

• 0:03
  Michael Smith, MD (Host): Welcome to Pediatrics in Practice, a CME podcast.
• 0:06
  I'm Dr.
• 0:07
  Mike.
• 0:07
  And with me is Dr.
• 0:08
  Sara McElroy, a pediatric hematologist and Director of the
• 0:12
  Stroke Program at Children's Mercy.
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  Today, we're talking about how to recognize and manage abnormalities
• 0:18
  on the CBC in children, and when those findings should prompt a closer
• 0:24
  look or a referral to hematology.
• 0:27
  Dr.
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  McElroy, welcome to the show.
• 0:29
  Sara McElroy, MD: Thank you.
• 0:30
  Glad to be here.
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  Host: Abnormalities on CBCs happen all the time, both in kid world, adult
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  world, you know, especially primary care.
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  So, what are the most frequent findings you see referred that
• 0:43
  maybe could have been managed at the primary care level before a referral?
• 0:48
  Sara McElroy, MD: Actually, I would say most things can be safely
• 0:51
  repeated prior to an immediate referral, and we'll probably discuss
• 0:55
  some exceptions to that later.
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  But I do have a few situations in particular that I think are
• 1:00
  helpful for people to know.
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  So if you see a decrease in any of the cell lines, so we're talking hemoglobin,
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  neutrophil count from platelet count, in a child who has a mild viral or
• 1:11
  bacterial infection, so transient bone marrow suppression is really common
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  during infection, particularly in kids.
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  And those changes typically normalize within a few weeks
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  after the infection has resolved.
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  I would generally say most of those kind of mild decreases definitely can be
• 1:28
  repeated later on after the child is well.
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  It doesn't necessarily warrant a referral to us.
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  A few other things.
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  So, microcytic anemia, really common in kids, a lot of times
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  it's due to iron deficiency.
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  So, mild to moderate anemia, that is definitely from iron deficiency.
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  The primary care provider can certainly manage that with oral iron supplementation
• 1:51
  and just repeating labs in a few months.
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  Most kids respond really well to that.
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  So, they don't always need to come and see us in hematology for that.
• 1:58
  And then, I would also just encourage if a CBC was drawn
• 2:02
  kind of just as like a well check, that the child's otherwise well.
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  And there were like really unexpected abnormalities on it, there is definitely
• 2:11
  lab error that can occur or lab artifact.
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  So, I would encourage, particularly in a well-child, if something very unexpected
• 2:19
  comes up, that really the next step is just to repeat that CBC and make sure that
• 2:23
  those were actually true findings on that because we do see that not infrequently.
• 2:27
  So, those are just a few kind of things I would note.
• 2:31
  Host: And I would assume too, how the patient is doing plays a role here, right?
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  So, you have a young child, asymptomatic, and there's a slight change one of
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  the CBC parameters, probably okay to go ahead and repeat and, you know,
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  see how they're doing down the line.
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  But you did mention there are some red flags, right?
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  There are some things that probably need to go to a specialist like you right away.
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  What are some of the red flags that you think we should refer right away to you?
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  Sara McElroy, MD: So, you know, I'm a hematologist, and the
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  CBC can show you some things that are more oncology related.
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  So, this is more oncology specific, but any report of a blast cell which is a
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  very immature type of white blood cell on a CBC, is very concerning for leukemia.
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  That should go straight to the ER probably, actually.
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  And then, a few other things.
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  So, a neutrophil count that is in the severe range, so I would call
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  that an absolute neutrophil count of less than five hundred in a
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  child that's either actively febrile or just really ill-appearing that
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  definitely should probably go to the emergency department as well.
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  And then, if we see pancytopenia, so all of the cell lines being low, so
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  hemoglobin, platelets, and neutrophil count all being low, and if any of
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  those are in the severe range or any combination of those in the severe range,
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  then usually that would warrant either the ER or coming to hematology first.
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  Sometimes providers can call us to get our advice on that.
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  And then, maybe just a few other things.
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  So in a patient who has anemia and then also has jaundice, so scleral icterus or
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  just kind of the yellow discoloration, that's concerning for a hemolytic process
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  that can sometimes be more severe.
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  So, I would say that would usually warrant coming to us pretty quickly.
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  I'll end this one with a severely low platelet count.
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  So, let's say a platelet count of less than 50 in a patient who is
• 4:22
  having abnormal bruising or bleeding symptoms or petechiae, that kind
• 4:26
  of concerns me a little bit more and warrants coming either to us
• 4:30
  directly or, if it's really low and the bleeding symptoms are significant,
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  maybe going to the emergency room.
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  Host: When you look at CBCs a lot in the primary care setting, isolated
• 4:41
  thrombocytopenia is something that is at least not uncommon and something
• 4:46
  that we have to deal with a lot.
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  So, what clinical or laboratory clues help you to distinguish an
• 4:52
  isolated thrombocytopenia from benign, transient, or something more serious?
• 4:58
  Sara McElroy, MD: Yeah.
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  With thrombocytopenia specifically, it probably depends on how low it is.
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  So if it's mild, rest of the CBC is normal, the child seems to be normal,
• 5:09
  not having any major symptoms, bleeding issues, I think that can be repeated.
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  And a mildly low count like, you know, between 100,000 and 150,000 you probably
• 5:20
  don't need to repeat that anytime soon.
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  Maybe at their next well-child check and just look at it there.
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  If it's much lower than that, maybe warrants repeating a little bit sooner.
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  But I always take into account what kind of symptoms the patient has.
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  And then, usually, we'll also get a little bit of history on the patient too,
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  just like clinically how they're doing.
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  Because sometimes a low platelet count could be a sign of something
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  maybe genetic that's been going on for longer could progress, might
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  warrant seeing us at some point.
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  So, there are some symptoms and signs that we look for with that.
• 5:53
  Host: I like what you said there where, you know, you're putting
• 5:55
  the symptoms together with the findings because I think sometimes as
• 6:00
  clinicians, we jump right to that data.
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  We jump right to the labs.
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  We look right at those numbers.
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  And we have to remember how the patient feels is actually probably the most
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  important thing and is going to drive how we interpret those labs, right?
• 6:16
  Sara McElroy, MD: Absolutely, totally agree with that.
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  Host: But it's easy to forget that when you have all these
• 6:20
  numbers in front of you, right?
• 6:22
  Sara McElroy, MD: Yeah.
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  The CDC has so many numbers associated with it, but it
• 6:27
  can sometimes be overwhelming.
• 6:28
  Host: I do want to talk about something that we see a lot too, so
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  you're drawing a CBC and maybe the child has a viral infection, maybe
• 6:38
  an ear infection or something like that, or some sort of recent illness.
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  How do you interpret the CBC and some maybe transient changes in
• 6:48
  the context of some of that stuff?
• 6:51
  Sara McElroy, MD: Even before I'm interpreting that CBC, encourage people
• 6:54
  to maybe—unless there's a real clinical indication to obtain a CBC, not every
• 7:00
  child who has an infection, mild viral infection, bacterial, you know, ear
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  infection probably doesn't need a CBC.
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  But in the event that it's drawn and there's mild infection, the findings
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  can be difficult to interpret.
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  So, that's why I would say if you're seeing any changes in the setting of
• 7:17
  the child having some kind of infection, obviously, you have to talk with the
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  family about what those look like.
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  They might get a little stressed, a little nervous.
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  But just reminding yourself, reminding the family that we see
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  these transient changes, they do usually resolve within a few weeks.
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  So, I usually recommend for providers to repeat them about four to six weeks
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  after the child has gotten better.
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  And then, just giving the family good return precautions if you do see like a
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  low neutrophil count saying, "Hey, you know, I think this will resolve soon.
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  But if the child starts to develop symptoms that are unexpected, like
• 7:50
  prolonged fevers or looking really ill-appearing, then that would be
• 7:53
  the indication to go ahead and check those labs sooner rather than waiting.
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  Host: You know, infection always is interesting to me too because the basic
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  idea, you get an infection, immune system activates, white count goes up.
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  It also depends on where that patient is in the infection, what stage they're
• 8:10
  at that's going to determine what changes you see in white count, right?
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  If the infection's just starting, you might not see any change.
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  Sara McElroy, MD: Correct.
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  Yeah.
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  You can see the white blood cell count be high, low, normal.
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  All bets are off with kids and infections
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  Host: Medications, Dr.
• 8:27
  McElroy, are there any medications that affect the CBC we should be aware of?
• 8:32
  Sara McElroy, MD: Yeah.
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  There are a lot of medications that have adverse reactions
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  that are related to CBCs.
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  I'd say the most common would be there are some medications that can be used
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  for certain psychiatric diagnoses that are very much known to cause a low
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  platelet count or a low neutrophil count.
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  A few of the antiepileptics can definitely be a culprit in
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  thrombocytopenia or neutropenia.
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  There's a lot more, but those are kind of the two that come to mind quickly.
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  But definitely, if those are on board and you see those blood count
• 9:02
  changes, likely it is related to that.
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  Host: So, let me ask you this too.
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  We talked a lot about referral, know those red flags, you know,
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  when to make that immediate referral, even go to the ER.
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  But if maybe the child is not emergently sick, but something's going on.
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  You've repeated the CBC, you're still seeing that abnormality,
• 9:24
  and you're like, "Okay."
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  Or the primary care doctor's like, "It's time to get this referral."
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  Is there any other labs at that point that the primary care provider should
• 9:34
  order and have ready for you to look at?
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  Or just send them over to you and you'll take care of all that?
• 9:40
  Sara McElroy, MD: Yeah, I think there's some labs that they could get
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  beforehand that's nice for us to know.
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  Of course, you know, if there's any level of discomfort with that, then certainly
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  they can put the referral into us.
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  We're happy to see them do that.
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  But a couple of notes.
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  So, I always say that the CBC is not complete in a patient with anemia
• 9:57
  until they've had a reticulocyte count.
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  And that doesn't come with a routine CBC.
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  You do have to order that separately.
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  That reticulocyte count just tells you how well the patient's
• 10:06
  bone marrow is responding to them having a low hemoglobin.
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  So if you see it being elevated, then there might be some kind of
• 10:13
  red blood cell loss or destructive process, whereas if that is low, then
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  it's more of a production problem.
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  So, I like to see that reticulocyte count.
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  It's very helpful to me.
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  Sometimes people will get a CBC and they won't get a differential,
• 10:26
  which is sometimes appropriate.
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  But if a patient has a leukopenia, a low white blood cell count, then
• 10:32
  they definitely need to add on that differential so that we know
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  which of the specific types of white blood cells is low, because
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  that helps us out a lot as well.
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  And then, I think, you know, if they have jaundice, of course, getting
• 10:43
  that hepatic function panel, looking at bilirubin is good to know.
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  I also like to see a peripheral smear.
• 10:51
  Not everyone's lab is going to do that, and that's okay.
• 10:54
  But if they have the opportunity to do a peripheral smear, that's really helpful
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  for me to know what the pathologist is seeing actually under the microscope.
• 11:02
  Host: So, what referral mistakes or misconceptions do you see most often?
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  Sara McElroy, MD: I think the one that comes to mind is where we get referrals
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  for patients with abnormal blood counts, but it was done at a lab where
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  they're using adult reference ranges, because pediatric reference ranges
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  are going to be different than adults.
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  And I just encourage providers to always, first of all, know what the
• 11:24
  reference ranges that are being used for the labs that they have drawn,
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  and then making sure that they're comparing their patient's numbers to
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  actual pediatric reference ranges.
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  Because that can oftentimes save a referral to us and cost to the family
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  and all that stuff, if we're making sure that we're using appropriate ranges.
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  And then, the differential, it will give you the percentages of the
• 11:47
  different white blood cells, and then will also give you absolute counts.
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  And we really go off of absolute counts when we're determining
• 11:53
  whether something's high or low and not based off of that percentage.
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  So, I see that occasionally where we will get referrals for a low percentage, but
• 12:02
  the absolute count is actually normal.
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  That's a good thing to know too.
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  And then, my last thing, also related to white blood cells, we'll get referrals
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  sometimes for leukopenia with the total white blood cell count being low.
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  But then, when we actually look at the absolute counts of the neutrophils,
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  the lymphocytes, they end up being normal, maybe on the low end of the
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  range of normal for both of them.
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  So, it makes the total look abnormal.
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  But I'm not worried about that total if the actual, like, specific
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  types of the cells are in the normal range, if that makes sense.
• 12:32
  Host: That does make sense.
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  And this has been fantastic information.
• 12:35
  Any last word for the listening audience about CBCs and referrals?
• 12:40
  Sara McElroy, MD: We're always available for a phone call if it's something
• 12:42
  that you're not sure if it needs a referral, then that's what we're here
• 12:46
  for is to kind of help guide with that.
• 12:47
  We can let you know "Hey, this is actually not super worrisome.
• 12:51
  You can just repeat this," or "Yeah, we definitely want to see him."
• 12:53
  So, we are available for that if it comes up.
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  But I think that's about it.
• 12:58
  Host: Fantastic.
• 12:59
  I really want to say thank you for coming on.
• 13:01
  I know you're very busy.
• 13:02
  This was great information.
• 13:04
  I'm glad you found the time.
• 13:05
  For more information, you can go to cmkc.link/4yd2epd.
• 13:15
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• 13:18
  and check out the entire podcast library for topics of interest to you.
• 13:23
  This is Pediatrics in Practice, a CME podcast.
• 13:26
  Thanks for listening.