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Introduction to lab values and normal ranges

Find out how health professionals use short-hand for labs and the meaning of normal ranges. Rishi is a pediatric infectious disease physician and works at Khan Academy. Created by Rishi Desai.

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  • leafers sapling style avatar for user Peter Collingridge
    How are blood cells counted? I assume no one counts 227 000 platelets manually.
    (24 votes)
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  • leaf green style avatar for user Tanishq
    How are glucose levels measured?
    (4 votes)
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  • spunky sam blue style avatar for user kattastrophik
    Hi! what does BUN mean in a clinical setting?
    (3 votes)
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    • leaf green style avatar for user Joanne
      BUN = Blood Urea Nitrogen. Since urea is filtered out by the kidney, BUN and creatinine are used to evaluate the health of the kidneys. Urea is a waste product of the breakdown of nitrogen containing molecules, such as proteins and nucleic acids. Creatinine is also removed by the kidneys and it is a waste product from muscle that is usually constant. If the kidneys are failing, BUN and creatinine are both high.
      (5 votes)
  • blobby green style avatar for user sachin.lavania
    I have always seen and put the BUN on top and Cr on bottom, vise versa of what was shown in this video.
    (3 votes)
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  • piceratops seed style avatar for user Byung Jung
    Please bear with me as I explain my thought process.

    For the normal range, I understood it as someone who can fall within the limits and not have a problem. For example, a WBC count of 5000 compared to 9,999. In this case, a PCP or treatment team would not consider the higher end value as an infection (or other reasons) until it breaks the 10,000 mark.

    What about a situation where a PT with a WBC count of 4500 "normally" but presents with a 9999 WBC after a CBC. Would this person be considered for "infection" or other reasons? I ask this because for someone with a normal WBC range of 9500, a 10,100 WBC count (increase of only 600) would be considered for infection, and I imagined (using the "normal values") a person (stated initially) with a 5499 WBC increase would still not be considered "infected".

    I was told looking at HX and understanding the whole situation is best, so would it be case by case? And when someone with that much change in WBC count regardless of breaking the higher end of "normal" WBC (i.e. 4500 to 9999) be treated for infection and started on broad spectrum antibiotics?
    (1 vote)
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    • leaf blue style avatar for user dysmnemonic
      Reference ranges for tests like a WCC are developed by testing healthy people to see what their results are like. The reference range is then calculated as the mean +/- 2 SD. This means that 95% of results for healthy people will be inside the reference range, while about 2.5% will be low and 2.5% will be high. This is why we tend to look for bigger changes on the test - a WCC of 10.1x10^³/mL is pretty unexciting, while a WCC of 20 will need further investigation.

      But it's definitely a case-by-case thing, and we're only looking at lab tests after doing a Hx & Ex. If the patient's clinical presentation is consistent with infection, we're going to treat them almost regardless of what the WCC is doing. If the WCC is grossly inappropriate for the clinical presentation, then we might also start looking for another problem that's causing unusual immune response.
      (3 votes)
  • aqualine ultimate style avatar for user Noah E.
    what process do most lab tests use after the blood is drawn?
    (2 votes)
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  • male robot hal style avatar for user dannyquil
    How do the numbers fit into the shorthand section? Is there another way other than just ordering the from the top left, down, up and to the left etc?
    (3 votes)
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  • leaf grey style avatar for user rjhogue
    Would love to see a variant on this video for those undergoing chemotherapy - not just want the numbers are, but what they mean - what matters, since our counts are typically not 'normal' ...
    (2 votes)
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  • aqualine ultimate style avatar for user Geetika Pachauri
    How does arranging the data in the stick diagram help??
    (1 vote)
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  • male robot johnny style avatar for user Marco Antonio Dávila Hernández
    Your explanations and details of the shorthand method are excellent. Although, here in Puerto Rico CMP's are usually ordered in which case the value of CO2 replaces the value of HCO3. It's been years since I've seen a Chem 7 or 10. I needed your example to refresh my memory. Thanks!
    (1 vote)
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Video transcript

So I have a slip of paper. Let's go through these lab values. I actually put down a number of values down that we're going to pretend for a moment are my labs. And you can see the range, and the units next to them. So let's go through it piece by piece. And actually, while I do it, I'm actually going to show you some shorthand techniques, so that you can understand, if you ever see this in the future, what it refers to. So this is some shorthand that people have come up with. This isn't necessarily something I've come up with. I learned it from folks ahead of me. But it's been used not just in the US, but most parts of the world. It's pretty uniform. So if you're looking at these labs, here's a quick way to transcribe them. So imagine that you have to quickly put it on a piece of paper and move on. This is how you would do it. So you would draw a little stick diagram like that. And in the far left, you'd put the number 5. And this refers to the first row, the White Blood Cell row. And we know that the value is 5,000, so that's what the 5 represents. And it's understood that that number is in thousands of cells per milliliter. So if you see a 5, you know we're talking about thousands of cells per milliliter. And the next question is, well, what are those types of cells, if you actually were to look at them? We know they're white blood cells. But exactly what type they are is actually in the six rows beneath. So these six rows tell you the breakdown of this number. So that's why they're percents. And so the 5,000 cells break down into segmented neutrophils. I'm going to write that as an S with a 61. And bands, there are 3% bands. Lymphocytes are 29%. And then we have monocytes at 4%, basophils at 1%, and eosinophils at 2%. So these percentages for the different types of white blood cells are going to add up to 100, right? So let's just double-check. We've got 7 and 29 is 36, and 3 is 39. Yep, 100%. So that's how you quickly can see the different types of white blood cells that are floating around in your body. That's what those numbers represent. So then the next two numbers, hemoglobin and hematocrit, go in the top and bottom of this stick diagram. And again, whenever you see these numbers like this, I could look at that and immediately figure out that that's the red blood cell content. Those two numbers both reflect red blood cell content in the blood. And then the last cell on this side represents the platelet count. And 227 represents 227,000 cells per microliter. So before, we were talking about milliliters for the white blood cells. But now, for the platelets, we're talking about microliters. And in fact, I'll put "cells" in quotes, because we know it's not really cells. These are little cell fragments that are the platelets. So that 227,000 tells you about how many platelet cell fragments are floating around in one microliter of blood. So that's the first chunk of data. So that's all this information, summarized very quickly in that stick diagram. Now let's move on to the chemistries. And so if someone orders a Chem 7, then that would be the first seven of these. And if they order a Chem 10, then that would be all 10 of these. So this is how you would draw this out as a stick diagram. It kind of goes like this. And the Chem 10, the last three, go in here. So the sodium goes in the top left. And below that is the 4.3 for potassium. And just going systematically all the way through it, so for chloride, it's 103. Bicarbonate goes as 22 right below that. And then the creatinine goes in this cell, 0.8. And then the blood urea nitrogen-- sometimes they call that the B-U-N, that's just the first letter of these three-- is 15. And then the fasting glucose is 92. And then the calcium goes in the top of this little wishbone-shaped stick diagram. That goes right there. The magnesium goes on this side. And the phosphate goes on this side. So that's the Chem 7 on top. And the Chem 10 would be all of that together. And then, at the bottom, we have some liver enzymes. And also, there's a stick diagram for that, as well, kind of a fast way to draw it. And it's basically just an x. So the top of the x is two numbers. So you usually write the total bilirubin like this, 1.1. And then you put a slash. And then you put the other number there, the direct bilirubin, 0.1. And then on the left, you put the AST. And on the right, you put the ALT. And at the bottom, you put the alkaline phosphatase, 76. So this is how the numbers break down. And so, again, if you ever see any of these stick diagrams and you're wondering what they refer to, now you have broken the code. You know what number goes where. So if you see, for example, this number at 22, you immediately know that they're talking about the ALT. So this is the way that people quickly diagram things. And now I know, when people look at labs, the first thing they want to know is, hey, is this good or bad? And so, they want to look at these values, and they want to compare them to the ranges. They want to say, hey, does this fit into the normal range that people expect? So let's talk about that. Let's talk about normal range and what normal means exactly, because I know that's the first thing most people will want to look at. So let me draw out what a normal curve would look like. So if you actually, let's say, took everybody, let's say 10,000-- it's not everybody, but let's say a big chunk of people-- 10,000 people and asked them all to tell you their white blood cell count. They will give you, of course, many different numbers. Probably wondering what you're doing with that information. But let's say they give you their answer. And let's say you plot it all on a curve, and you draw a little diagram. This would be basically what you would find. You'd say, OK, most people have a white blood cell-- and this is white blood cell count. Actually, sorry. This is white blood cell count down here. And this is, of course, in thousands. We said thousands per milliliter, thousands of cells per milliliter. And this is frequency. This is the number of people. I'll just write f for frequency. So you would say, OK, while there are a lot of people in this range right here-- and in fact, 95% of people fall in to this middle section in this area. So this is definitely the bulk of people that fit between 4.5 and 10. And that's actually how most of these ranges are decided upon. They say, OK, where do the bulk of folks lie? And it's usually between those numbers that are in the range. And that also means, if you think about it, that there is, of course, somebody out here and somebody up here, right? I mean, that is, by definition, going to happen. You're going to have 5% of people in one of those two tails combined. So whenever you see a range, just keep in mind that there is some normal variance, they're called, that kind of go above or below that range. But that range usually captures the majority of folks. So when thinking about that, when thinking about what exactly goes into a normal range, consider some of the things that could make what is normal differ. So for example, let's say I check someone's hematocrit. Let's say I'm looking at the hematocrit, and I want to find out if it's normal or not. If I look at a baby's hematocrit, but I use, let's say, an adult range, then it would be very, very unusually high. So a newborn baby has a very high hematocrit, so I really should be comparing it to other newborn babies. So age is really important to consider. So you want to make sure that the range of values is age-appropriate. You also need to make sure that gender is considered. So for example, the normal range for men's hematocrit is a little bit higher than the normal range for women's hematocrit. So range matters for age and also for gender. Now, different labs will also differ. So it's actually quite interesting. You can even go online and see what the normal range is for a lot of these things I have here. And the numbers will be a little bit different from what I've shown you. So if you go from one lab to another, you'll get different numbers. And in fact, lab technique also matters. So even within a lab, depending on the technique that they use to get an answer to something, the range could differ. And that actually matters, particularly for things like this. So these IUs that I put down here, they stand for units, or international units. And that's specific to a certain type of lab assay that's done. And again, that depends on the exact assay that's done. And that's going to change the range of values that you get there. So consider the technique. And finally, consider this situation. So if you have, let's say, a person who is supposed to come in for a fasting glucose. And usually, you're told, just don't eat anything overnight. And don't have breakfast. And come in and get your blood taken first thing in the morning. That's a pretty common scenario. Then you would have a normal fasting glucose. And it should be below 100. But let's say, by accident, you decide to have a little snack in the morning, because that's your usual thing. You have some toast. Your blood glucose could go up as a result. So that glucose result could be OK, if someone knows that you didn't fast, really. You had a little snack. So that situation changed. So your metabolism is going to make that range go up. So only for fasting glucose is the number below 100 normal. Otherwise, it could be higher. Now consider a situation where you're taking a medication. Let's say you're on a medication that causes your potassium to go down. So you're on a drug. It causes potassium to leave your kidneys and go into the urine. Your potassium value would then go down. I would expect it to be lower, right? Because you're taking your medication. And so some of these ranges are going to change, depending on what medications you take, what you had for breakfast that day, or not had for breakfast, what kind of medical conditions you have. So it's going to definitely depend on the situation. So whenever you look at ranges and values, and you want to see if you are in the normal range, just consider all these things that could explain why your number may or may not be within that range.