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# Units for common medical lab values

## Video transcript

in the last video we talked about normal blood values and the ranges as well but we didn't really get to unit so I thought we would talk about that now now the units I think the best way to think about units and the information they tell you is to break into two basic categories one is amount and the other is function and we'll talk about each of them in turn so what I mean by amount is let's say that you want to convey to someone information about the amount of something what are the different ways you could do it well one way one way you could do it is you could say well what about the mass let's let's figure out the mass of whatever it is you're interested in and the volume and you could convey information you to say well it's maybe five grams in a liter or or in the case of hemoglobin you could say it's 15 grams in a deciliter and a deciliter just means one tenth of a liter you can actually convey information that way and and it's actually done a few times you can see on this list of lab values so you can see that we do that for hemoglobin and we also do it down here for blood urea nitrogen the fasting glucose we do it for calcium we do it for phosphate a few things total bilirubin direct bilirubin so this strategy of conveying information by simply figuring out the mass over a volume is used a few times but here's something that I think a lot of people sometimes miss in lab values and that's the fact that you can actually compare things to one another so I could for example I could look at this list and say well you know hemoglobin at 15 grams in a deciliter but I only have 15 milligrams of blood urea nitrogen in a deciliter so in one deciliter the same volume I have a thousand times more hemoglobin than I do blood urea nitrogen by mass that's actually quite interesting because that tells you it seems on the surface at least that hemoglobin by mass then obviously is much much more common in the blood than blood urea nitrogen so that's one way to talk about the amount of something now another way of talking about the amount of something and switch colors would be to talk about the just to count it up just to actually literally just go and count up the number of something that you find in a certain volume of blood and we do that too sometimes we actually will count and let's say for white blood cells we actually count up 5,000 cells in one milliliter or for platelets you might say there are 227,000 and output cells in quotes because there's cell fragments in a microliter and even looking at those two microliter versus milliliter you can see that there are way more platelets in the same volume than there are white blood cells they may be smaller but there are many more of them so this is actually the second way to talk about amount now if you look through this list do you see any other examples of number of something in a volume and and if they answer if you're thinking no then I'm going to point something out to you that might surprise you think about these mil equivalents per liter all of those ions or mil equivalents per liter right and so thinking about what mil equivalent means maybe we should use an example here to to make it a little bit more concrete maybe this would be a good example sodium so I have here a sodium and remember sodium is a cation it's one charge so sodium have I have 141 Milic with length of it and that's actually the same as saying that I have 0.14 one equivalence right because we know milli is just a thousandth so that's the same thing as that and we know that because sodium has just one positive charge that in terms of equivalence one mole of sodium equals 1 mole sodium equals one equivalent of sodium therefore if I have 0.14 one equivalence of sodium I have exactly the same number 0.14 one moles of sodium and you know that moles this is just abogados number right this is just 6.02 times 10 to the 23rd just a big big number so if I actually multiplied this times this actually the whole thing obviously and I actually just did it right here with my calculator you can actually find that this 0.14 one times 6.02 times 10 to the 23rd is about eight point five times ten to the twenty two sodium ions sodium ions so if I was to literally count them up it would obviously take forever to count this huge number of ions up but if I was to do it that's all that is is just a number over in this case what do we have a liter that's a volume right so in one liter that's how many sodium ions I have so again it's just a number over a volume so it's really no different but I think the term milli equivalent I think can be a little bit surprising for folks to see that and so we don't think of it always as a number now the third way to think about amount would be a percent and one example would be right here all these numbers so these are all percents and here these percents are of a number so these are all percents of that white blood cell number so that would be a percent of number over volume right so that's thanked for example for bands three percent times five thousand per milliliter so that would be a example one another way to think about percent would be like this one right here you think about what is hematocrit mean forty five percent what is that percent of that's a percent of total blood volume so if I took the total blood volume right whatever that is I just take let's say some blood out of my arm and let's say it's 10 milliliters then forty five percent of it or 4.5 milliliters would actually be red blood cells and the rest the rest of that fluid would be mostly water of course but in that water would be proteins and immunoglobulins and all sorts of things that help us stay healthy so that percent represents just how much of my total blood volume is taken up by red blood cells that's what that number is now we've talked about amounts in three ways right but I've also mentioned function at the bottom I talked about function in the beginning of this so now imagine that you have a situation let's say you have a little enzyme I'm going to draw it here is little Y and let's say enzyme Y has a job and this enzymes job is to take little molecules like this let's say five of them and add little red things to them so it's supposed to add little red things to them and you let this go on for five minutes you basically just keep an eye on enzyme Y and you see how many does it convert and you find out that in the end of five minutes and actually was able to convert four of them so you get four converted in five minutes so so far so good right that's fine four were converted now you have another person they have enzyme Y as well and they have more of it they actually have more of it so they have more enzyme Y than the first person and this person has the same task or you basically give them a bunch of protein or let's say these little purple molecules whatever they are and you say well how many can they convert in five minutes and you might think well obviously they have more of the red stuff I'm sorry there's more the yellow yellow enzyme Y protein so if they have more of the enzyme Y protein they can obviously do more than person one this is person one up here let's say this is person one and this is person two down here so person two after five minutes let's say you time it they actually convert three so they were able to convert three and five minutes are up so a little surprising but now you think back on this and you say okay well if I was let's say to just figure out a amount of an enzyme let's say your job just as in part one was to figure out the amount of an enzyme and I did it by let's say mass I'd you know use the mass over volume of the enzyme then person two would look like they have more over here or if I over here two would look like they have more or if I let's say did the number of enzyme then again person two looks like they have more right or if I did let's say some sort of percent I don't know let's say percent of all enzymes again person two looks like they have more because they have just more of the enzyme around right but if you look at function if you actually look at the amount of work that's being done by these enzymes or the outcome of this enzyme then clearly person one actually wins out they have more of the work done than person two so if you're looking at actual activity and that's what this is when I say function you're looking at enzyme activity or sometimes it's even hormone activity if you're looking at the activity then that would be a different story so actually let me make a little bit of space here so function really alludes to me give you a nice aerial so this alludes to hormone hormone or enzyme enzyme activity and in this case person one would actually have a higher number because they have more enzyme activity in this case and so all three of these these at the bottom are examples of looking at activity so whenever you see I you or you that refers to international units or units so it's a way of standardizing across the entire globe or sometimes if it's through a set of labs just in one country how we look at the function of a certain enzyme and so anytime you see I you over L it's not really telling you about the amount of an enzyme although of course you would expect that there would be some correlation but it really tells you more about the function of an enzyme