Lab Values and Concentrations
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.
Introduction to lab values and normal ranges
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- So I have a slip of paper. Let's go through these lab values.
- I actually put down a number of values 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 short hand techniques so you can understand, if you ever see this in the future, what it refers to.
- So some short hand 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 U.S., 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 you
- have to quickly put it on a piece of paper and move on. This is how you would do it.
- So you 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 the value is 5000 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 were to actually 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 5000 cells break down into:
- Segmented neutrophils (I'm gonna 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 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 when you see these numbers like this I could look at that and immediately figure out 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 thousand 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, it's 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 of this information kind of summarized
- very quickly in that stick diagram.
- Now let's move on to the chemistries.
- So if someone orders a chem 7, then that'd be the first seven of these. And if they order a chem 10
- then that would be all ten of these.
- So this is how you would kind of 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 Postassium.
- And you're just going systematically all the way through it. So for Chloride it's 103, and bicarbonate goes, it's 22, right below that,
- and the Creatinine goes in this cell, 0.8, and the blood urea nitrogen, sometimes they call that the BUN,
- 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 kind of together.
- And then 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 is 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 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. This is how the numbers kind of break down, so again if you ever see any of these stick
- diagrams and you're wondering what they refer to. Now you kind of have broken the code, you know what number goes where.
- So if you see, for example, this number, the 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? 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 took
- everybody, let's say 10,000- but it's not everybody, but it's 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.
- They're probably wondering what you're doing with that information. But let's say they give you their answer.
- And 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- okay most people have a white blood cell- and this is white blood cell count down here- and this is of course in thousands, we said.
- Thousands of cells per mililiter. And this is frequency, this is the number of people. I'll just write "f" for frequency.
- So you'd say- okay while there are a lot of people kind of in this range right here, and in fact 95% of people fall into 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 okay 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's of course somebody out here, and somebody up here. I mean that is by definition going to happen.
- You are going to have 5% of people in one of those two tails combined. So whenever you see a range, just keep in mind, 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" different. So for example let's say I may 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 an adult's 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 want 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 ranges
- for a lot of these things that I have here, and the numbers will be a little different from what I have 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 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 International Units.
- And that's specific to a 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 the 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, you know don't eat anything overnight and
- don't have breakfast and come in and get your blood taken first thing in the morning. It'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.
- Umm, your blood glucose could go up as a result. So that glucose result could be okay if someone knows that you didn't fast really,
- you had a little snack. So that situation changed, so you're 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 makes your potassium go down.
- So you're on a drug that causes potassium to leave your kidneys and go into your urine. Your potassium value would
- then go down. I would expect it to be lower right? Because you're taking your medication. 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're in the normal range, just consider all of these things
- that could explain why your number may or may not be within that range.
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