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Lab Test Quiz: How Well Do You Understand Your RBC Index Tests?

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Published on May 1, 2015

Dr. Susan Leclair, laboratory scientist and professor at the University of Massachusetts Dartmouth, wraps up our 6-part series on red blood cell indices.  Pull out your notes and refresh your memory because the professorial side of Dr. Leclair emerges in this final video installment.  In the form of a 4-question quiz, she walks you through medical school in less than 10 minutes. Be prepared to answer questions about anemia, MCV, RDW, and vitamin B and folic acid deficiencies.  “Passing” this quiz means you have a clearer understanding of the red blood cell index tests that your doctor may order. 

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Transcript | Lab Test Quiz: How Well Do You Understand Your RBC Index Tests?

Please remember the opinions expressed on Patient Power are not necessarily the views of our sponsors, contributors, partners or Patient Power. Our discussions are not a substitute for seeking medical advice or care from your own doctor. That’s how you’ll get care that’s most appropriate for you.

Dr. Leclair:

Well, welcome back to a continuing discussion, maybe an overly long continuing discussion of red cells, but today is going to be a quiz, mostly.  You know about hemoglobins.  You know about  hematocrits now, mostly.  You know about indices, so let's spend some time using them.

I have a—I always love doing this to people when they have to answer back.  You can't answer back so that I can here you hear you, but I expect you to answer back at least to the computer screen.  You have a person who has got a hemoglobin on the low side, and when—so that suggests an anemia of some sort.  Now you want to know what's it caused by.  Okay.  You look at the MCV and the MCV is also on the low side.  What could be causing it?

And I'm going to count to 10, and you can answer it.  Okay, so I count fast.  Small means difficulty with hemoglobin production. Difficulty with hemoglobin production means iron, exposure to heavy metals, anemia of chronic disease, chronic inflammatory disease, and an inherited disease called thalassemia.  When you look at it you say, okay, so now, you can always figure this one out.  That would be serum iron, serum ferritin, maybe total iron-binding capacity.  Maybe we should look at tests for chronic inflammatory disease, maybe a serum lead if you happen to be working in a battery plant.  You can see how those tests kind of logically follow from that.

You have two—question number two.  You have two people that both of them have the same hemoglobin, but it's on the low side. Let's make it a 10.  So that's low.  Both of them have small cells.  Okay.  Now you're thinking iron, heavy metals, inflammatory disease—this is called medical school in 20 minutes—thalassemia.

Now look at the RDW.  The RDW is elevated, significantly elevated.  Do you think that this patient needs intervention, or do you think that this patient could go home and take some iron, go home and take some aspirin if it's chronic inflammatory disease, you know.  Kind of move along gently?  What would you say because the RDW is increased?

Well, if the RDW is increased, that probably means the marrow is under stress.  If the marrow is under stress—I love hematology. I love these cells.  I don't want marrows to be under stress under any condition. So I would immediately think that the logical thing to do would be find out what the cause is and fix it, because I don't think that with an RDW that's increased it's a really good idea to let your marrow continue to fumble and strain and stress and worry unnecessarily.  So with an RDW that's increased, I'm thinking maybe intervention is a little more likely.

Question number three, you have a person with an anemia.  We're going to stick with 10 grams of hemoglobin.  It's a nice number. So they're a little on the anemic side, a little tired, a little bit out of breath every now and then, but their MCV is increased, significantly increased—not just a little but significantly increased.  Hmmm.  What could that be?  One, two, three.)                                                                  

You should have flipped back in your notes.  That would have been either vitamin B12 or folic acid deficiency, possibly liver but probably unlikely, because it doesn't happen all that often.  So what tests would you order?  Oh, let's see.  How about a B12 level or a folic acid level to find out if that's the cause.  Now again I had those—I now have two people, both with the same MCV and it's large, and the RDW is increased, significantly in one, but it's not so bad on the other.

Just like the first example, I would think that if the RDW is Increased, then there's something significantly wrong.  Something needs intervention here sooner than to say to somebody, gee, you should eat more spinach, because folic acid is found in vegetables.  You see the difference between them and how you use these things in the determination of an anemia?                                                                         

Next case, again you have a 10-gram hemoglobin, but the MCV is within reference range.  Hmmm.  That means it's not iron.  It's not exposure to heavy metals.  It's not anemia or chronic disease.  It's not thalassemia.  But it's also not folic acid, it's not B12, and it's not liver function.  What could it be?  I mean, what else is there?

Well, for red cells there's that membrane we talked about. Something could be going on with the membrane that's causing

these cells to die sooner.  It's supposed to have enzymes in, so maybe there's something wrong with the enzymes in the cells.  Or maybe there's something else going on, that instead of me just hitting my hand up against the side of this chair I did get into a car accident.  So now all of a sudden I've lost a considerable amount of blood, but I don't have a deficiency in anything.  I don't have an overabundance in anything either.  I just have a loss of blood.  So I have normal-size cells, although I don't have as many as I should.

Or I do have something that's causing these cells to die faster than they should.  These are called hemolytic anemias, and they're some of the hardest ones in the world to track down on causes, because there are so many different kinds of causes.  You had a spider bite, sting actually, and the venom caused it.  If you're allergic to wasps and hornets and bees and you got stung, the venom caused it.  You were out in the sun worshipping the  sun god in June or July of this year, and you liberally layered yourself with frying oil—excuse me, that's called tanning lotion. And you sat out there a tad too long, and you came in beet red with some blisters.  Oh, okay.  You burnt yourself. All of those red blood cells that were in the skin that were close to that area got fried.  You got hemolyzed.  You did the same with cold.  You do it sometimes with different medications. And sometimes you can do it with abnormal tumors that have different kinds of blood vessels, so these cells will change.

So you can get a situation where in all of these the hemoglobin never changed, but the MCVs helped you determine what the cause was.  The RDW helped you determine whether or not there was some kind of intervention that was needed, gives you a more efficient, again more focused progress.  Most people in the world if they're going to have an anemia, have one that's iron deficient.  Those who have trouble with diet, starvation, anorexia, fad diets, you know, the ones where you only eat hot dogs for four days, they're going to have trouble with folic acid and with B12.

The middle group, that hemolytic process literally has hundreds of possible causes, and it's the one that's going to cause the most amount of difficulty in being able to determine what the root cause is. 

Okay.  I think our time is up.  Send me questions at questions@patientpower.info.  And remember, knowledge is an important weapon to have.  See you next time.  Bye-bye. 

Please remember the opinions expressed on Patient Power are not necessarily the views of our sponsors, contributors, partners or Patient Power. Our discussions are not a substitute for seeking medical advice or care from your own doctor. That’s how you’ll get care that’s most appropriate for you.

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