Lab Testing in Hematology Flashcards
A 16 yo female presents requesting birth control. Do you order any tests?
probably a pregnancy test
so might as well do a dipstick UA
some clinics rec to screen a Hgb just for screening (?)
What’s the better value? Just ordering the Hgb, or ordering the whole CBC? (If your clinic lets you split them out)
the CBC is much more valuable if you understand what the other numbers mean you can tell why the Hgb is low
Why should you just get the CBC with diff?
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
What machine runs the CBC?
automated hemocytometer
uses absorbence spectrometry
What is an RBC?
of RBCs in measured volum eof blood
increased RBC is erythroctytosis or polycythemia
decreased is anemia (differential for anemia will be a MC question)
What is another term for relative polycythemia?
hemoconcentration
What is the cause of a primary absolute polycythemia?
a neoplastic proliferation of RBCs INDEPENDENT of erythropoietin (polycythemia vera)
What is the secondary absolute polycythemia from?
anything that increases erythropoietin (so anything that decreases oxygen delivery to tissues–small RBCs, asthma, COPD, or rarely from a tumor that secretes erythropoietin)
-What is artifactual polycythemia?
when the machine mistakes something else for red cells (big platelets and parasites - usually plasmodium malariae)
What should your first step be after you see an increased RBC?
exclude artifact and then look at the MCV
What things should you think about if there is a high MCV?
…
What things should you think about if there is a normal MCV?
Take hx and look at other labs: Evaluate O2 level Hemoconcentrated? get blood gas Consider getting an erythropoietin level ...
Low MCV…
….
How is the Hgb measured?
machine lyses an aliquot of the specimen, sulfates the Hgb and then measures the concentration using infrared absorbence
Can the machine tell the difference between Hgb inside and outside the RBCs?
NO
Side note: what are the three definitions of anemia?
low Hgb
low RBCs
low Hct
any of these being low means the patient has an anemia
(THIS IS GOING TO BE AN MC ?)
What will the Hgb be in a polycythemia?
high
Sometimes the machine will misinterpret something else as hemoglobin so it will be falsely high. What are the two main things?
triglycerides
bilirubin
Hgb x # = HCT
x3
If (Hgbx3) - HCT is over +2, what is happening?
either free hemoglobin (lysed RBcs), something is interfering with the Hgb measurement (triglycerides or bili) or RBCs were sticking together in the machine
HCT used to be physically measured, but now it’s calculated by what?
the machine does it with (MCV x RBC)/sample volume
reported as a percentage
HIgh hematocrit usually means what?
polycythemia usually
If RBCs are sticking together (like in mono and cold agglutinins), what lab abnormalities will you see?
low RBCs, normal Hgb, low HCT, high MCV
and the Hgbx 2 - HCT > 2
True or false: it’s ok to ignore an abnormal MCV if the patient is not anemic.
FALSE
your hemoglobin, RBC count and HCT can be normal even with severe B12 deficiency
Causes of low mCV with RDW increased
….
Causes of low MCV with normal RDW?
111
MCV normal and normal RDW?
…
MCV Normal and RDW increased?
1111
MCV and RDW high?
….
MCV High and normal RDW
….
In healthy adults the MCV will change only very gradually unless there is what happening?
massive hemolysis
massive pH or electrlyte shifts
transfusion
or specimen error
Why is the TREND in the MCV as important as an abnormal MCV?
because there is a huge wide range of normal for MCV
An infant with anemia and a low MCV…do they have a microcytic anemia?
maybe, but not if they recently had a transfusion because they get adult RBCs and the MCV is lower for adult RBCs than infants
What is the formula for MCH?
Hgb x 10/Hct/RBC cells
Not really useful
How is MCHC calculated?
Hgb/total red cell volume
What’s the word for low mCHC?
hypochromic - means decreased Hgb in their RBCs
Does a normal MCHC hepl you?
not really because it can lag behind a hypochromic morphology
High MCHC is hyperchromc or machine artifact. From what?
the same things as the high hemoglobin artifacts : triglyceries, bili, hemolysis, free Hgb, RBCs sticking together
Red cell distribution of width is also calculated by the machine. Is it helpful?
use it along with the MCV as a first step in evaluating microcytic anemia (large RDW suggests IDA)
