Lab Testing in Hematology

Question 1

A 16 yo female presents requesting birth control. Do you order any tests?

Answer 1

probably a pregnancy test
so might as well do a dipstick UA

some clinics rec to screen a Hgb just for screening (?)

Question 2

What’s the better value? Just ordering the Hgb, or ordering the whole CBC? (If your clinic lets you split them out)

Answer 2

the CBC is much more valuable if you understand what the other numbers mean you can tell why the Hgb is low

Question 3

Why should you just get the CBC with diff?

Answer 3

Because in most labs, they’re all run on the same machine and the machine is automatically going to do the whole thing. some will even do a blood smear! Plus it really doesn’t make any difference in cost. (Hgb, CBC, CBC + Diff cost the same in billing)

BUT in many hospitals, if you only order the Hgb, that’s the only data you’ll get back even though the machine ran the whole CBC w/ diff

Question 4

What machine runs the CBC?

Answer 4

automated hemocytometer

uses absorbence spectrometry

Question 5

What is an RBC?

Answer 5

of RBCs in measured volum eof blood

increased RBC is erythroctytosis or polycythemia
decreased is anemia (differential for anemia will be a MC question)

Question 6

What is another term for relative polycythemia?

Answer 6

hemoconcentration

Question 7

What is the cause of a primary absolute polycythemia?

Answer 7

a neoplastic proliferation of RBCs INDEPENDENT of erythropoietin (polycythemia vera)

Question 8

What is the secondary absolute polycythemia from?

Answer 8

anything that increases erythropoietin (so anything that decreases oxygen delivery to tissues–small RBCs, asthma, COPD, or rarely from a tumor that secretes erythropoietin)

Question 9

-What is artifactual polycythemia?

Answer 9

when the machine mistakes something else for red cells (big platelets and parasites - usually plasmodium malariae)

Question 10

What should your first step be after you see an increased RBC?

Answer 10

exclude artifact and then look at the MCV

Question 11

What things should you think about if there is a high MCV?

Answer 11

…

Question 12

What things should you think about if there is a normal MCV?

Answer 12

Take hx and look at other labs:
Evaluate O2 level
Hemoconcentrated?
get blood gas
Consider getting an erythropoietin level
...

Question 13

Low MCV…

Answer 13

….

Question 14

How is the Hgb measured?

Answer 14

machine lyses an aliquot of the specimen, sulfates the Hgb and then measures the concentration using infrared absorbence

Question 15

Can the machine tell the difference between Hgb inside and outside the RBCs?

Answer 15

NO

Question 16

Side note: what are the three definitions of anemia?

Answer 16

low Hgb
low RBCs
low Hct

any of these being low means the patient has an anemia

(THIS IS GOING TO BE AN MC ?)

Question 17

What will the Hgb be in a polycythemia?

Answer 17

high

Question 18

Sometimes the machine will misinterpret something else as hemoglobin so it will be falsely high. What are the two main things?

Answer 18

triglycerides

bilirubin

Question 19

Hgb x # = HCT

Answer 19

x3

Question 20

If (Hgbx3) - HCT is over +2, what is happening?

Answer 20

either free hemoglobin (lysed RBcs), something is interfering with the Hgb measurement (triglycerides or bili) or RBCs were sticking together in the machine

Question 21

HCT used to be physically measured, but now it’s calculated by what?

Answer 21

the machine does it with (MCV x RBC)/sample volume

reported as a percentage

Question 22

HIgh hematocrit usually means what?

Answer 22

polycythemia usually

Question 23

If RBCs are sticking together (like in mono and cold agglutinins), what lab abnormalities will you see?

Answer 23

low RBCs, normal Hgb, low HCT, high MCV

and the Hgbx 2 - HCT > 2

Question 24

True or false: it’s ok to ignore an abnormal MCV if the patient is not anemic.

Answer 24

FALSE

your hemoglobin, RBC count and HCT can be normal even with severe B12 deficiency

Question 25

Causes of low mCV with RDW increased

Answer 25

….

Question 26

Causes of low MCV with normal RDW?

Answer 26

111

Question 27

MCV normal and normal RDW?

Answer 27

…

Question 28

MCV Normal and RDW increased?

Answer 28

1111

Question 29

MCV and RDW high?

Answer 29

….

Question 30

MCV High and normal RDW

Answer 30

….

Question 31

In healthy adults the MCV will change only very gradually unless there is what happening?

Answer 31

massive hemolysis
massive pH or electrlyte shifts
transfusion
or specimen error

Question 32

Why is the TREND in the MCV as important as an abnormal MCV?

Answer 32

because there is a huge wide range of normal for MCV

Question 33

An infant with anemia and a low MCV…do they have a microcytic anemia?

Answer 33

maybe, but not if they recently had a transfusion because they get adult RBCs and the MCV is lower for adult RBCs than infants

Question 34

What is the formula for MCH?

Answer 34

Hgb x 10/Hct/RBC cells

Not really useful

Question 35

How is MCHC calculated?

Answer 35

Hgb/total red cell volume

Question 36

What’s the word for low mCHC?

Answer 36

hypochromic - means decreased Hgb in their RBCs

Question 37

Does a normal MCHC hepl you?

Answer 37

not really because it can lag behind a hypochromic morphology

Question 38

High MCHC is hyperchromc or machine artifact. From what?

Answer 38

the same things as the high hemoglobin artifacts : triglyceries, bili, hemolysis, free Hgb, RBCs sticking together

Question 39

Red cell distribution of width is also calculated by the machine. Is it helpful?

Answer 39

use it along with the MCV as a first step in evaluating microcytic anemia (large RDW suggests IDA)