Red Blood Cells Part 1

Question 1

what is RBC count, Hgb, and HCT used for in the erythron?

Answer 1

used to assess RBC mass, normally will go up or down together; also used to calculate other RBC indices

Question 2

what is MCV, MCHC, MCH, RDW used for in the erythron?

Answer 2

used to assess size (MCV and RDW) and hemoglobin content (MCHC and MCH) of RBCs; these patterns of changes are used when assessing anemia

Question 3

what components on the erythron are directly measured? (2)

Answer 3

1. RBC: red blood cell count
2. HGB: hemoglobin concentration

Question 4

what components on the erythron are calculated? (5) which are primarily used to classify anemias?

Answer 4

1. HCT: hematocrit
2. MCV: mean corpsuscular volume
3. MCH: mean corpuscular hemoglobin
4. MCHC: mean corpuscular hemoglobin concentration
5. RDW: red cell distribution

MCV, MCH, MCHC, and RDW are used to classify anemias

Question 5

how do you evaluate nucleated RBCs?

Answer 5

BLOOD SMEAR ONLY because all machines count nRBCs as WBCs

Question 6

describe PCV and HCT

Answer 6

both are reported as % of blood occupied by RBCs;

PCV: determined by centrifuging blood in a small tube and the MEASURING the value

HCT: CALCULATED by automatic analyzers based on average red blood cells size (MCV) and number of RBCs (HCT = RBC x MCV)

Question 7

why would HCT and PCV differ? (they are usually roughly the same)

Answer 7

plasma gets trapped between RBCs when spinning a PCV, so PCV is slightly higher than HCT; but the difference shouldn’t be greater than 2-3%

Question 8

how is hemoglobin concentration measured? when could you see a false increase (3) what SHOULD Hgb be?

Answer 8

measured based on light transmission

can see a false increase with things that block light transmission:
1. lipemia
2. RBC agglutination
3. Heinz bodies

Hgb SHOULD be approx 1/3 of the HCT or PCV

Question 9

what would cause a disproportionate false increase of Hgb?

Answer 9

RBC lysis! can be artifact if was a hard blood draw or sample is old; can tell if actually true increase by looking at MCHC (more sensitive, looks at hemoglobin content)

Question 10

what is MCV?

Answer 10

mean corpuscular volume; a measure of the average volume/size of erythrocytes; used to estimate mean cell volume

if within reference range: normocytic
if greater than reference range: macrocytic
if less than reference range: microcytic

Question 11

when is increased MCV/macrocytosis seen (RBCs larger than normal)? (6)

Answer 11

1. reticulocytosis: regenerative anemia is most common cause
2. FeLV infection in cats
3. congenital in poodles (rare)
4. vitamin B12 or folate deficiency (rarely seen with macrocytosis in domestic species)

artifactual:
5. RBC agglutination: IMHA can cause
6. delayed sample processing (cell swelling artifact)

Question 12

when is decreased MCV/microcytosis: RBCs smaller than usually seen? (4)

Answer 12

1. iron deficiency!!! most common cause; RBCs compensate by increasing cell division to compensate for decreased iron to increase hemoglobin content
2. young animals: physiologic iron deficiency
3. portosystemic shunt (FYI)
4. asian breeds

Question 13

what is MCH?

Answer 13

mean cellular hemoglobin; average amount of hemoglobin per RBC

Question 14

what is decreased MCH and MCHC called and why? what are the 2 causes of it?

Answer 14

decreased MCH and MCHC is called hypochromia, since the cells look paler than usual due to decreased hemoglobin in the cell

causes are:
1. reticulocytosis/polychromasia: haven’t finished Hgb synthesis yet
2. iron deficiency (except in cats): can’t form as much Hgb

Question 14

what is MCHC?

Answer 14

mean cellular hemoglobin concentration; average amount of hemoglobin concentration per mass of RBCs

Question 15

when would you see increased MCHC?

Answer 15

it’s an artifact!! there is no physiological mechanism for forming too much hemoglobin, as Hgb synthesis stops at max concentration;
would only see this in cases of hemolysis, where there is more free hemoglobin to detect, and with anything that causes an false/artifactual increase in Hgb (like lipemia)

Question 16

what is RDW?

Answer 16

red cell distribution width; determined by automated analyzers; is a statistical expression of RBC size variation (higher number = greater variation); often increases before MCV is outside reference interval but will NOT be abnormal is all RBCs are smaller or if ALL RBCs are larger

Question 17

what is reticulocyte count?

Answer 17

a measure of the number of immature RBCs (reticulocytes) in circulation to assess the bone marow’s response to anemia

Question 18

what does reticulocytosis in the presence of anemia indicate?

Answer 18

that the anemia is regenerative

Question 19

describe 3 species differences in reticulocytes

Answer 19

1. mild numbers are normal in the dog (mild polychromasia is expected)
2. horses don’t usually release reticulocytes from the bone marrow, even with marked anemia; horses like to keep RBCs in the bone marrow until mature, so will have to do repeat CBCs to see if increasing HCT (if so, regenerative anemia is likely)
3. cats usually have very few reticulocytes in health and can have aggregate reticulocytes (circulate only for a few days, are best to measure to see if anemia is regenerative) or punctuate reticulocytes (circulate for weeks, not as helpful because cat could have had anemia two weeks ago)

Question 20

what are the 3 ways to classify anemia?

Answer 20

1. bone marrow response: regenerative versus non-regenerative; use reticulocyte count, polychromasia on a blood smear, direct examination of bone marrow, or serial PCVs/HCTs
2. RBC indices: MCH, MCHC, RDW
3. underlying mechansism

Question 21

describe reference intervals (4)

Answer 21

1. set of values used to interpret lab results
2. range that 95% of healthy individuals will fall into, MEANING that 5% of healthy individuals will fall outside RI
3. ideally would use 120 or more healthy individuals representative of the general population to establish the RI but this is hard to gather so 40 is the minimum
4. examples of subgroups include: male vs. female, immature vs. geriatric, breed differences

Question 22

explain reticulocyte maturation in peripheral blood, including species specific considerations

Answer 22

all RBCs begin with a nucleus up to the metarubricyte form; the first form without a nucleus is the reticulocyte/polychromatophil, which is the final form before the mature RBC

Question 23

interpret reticulocyte counts in dogs and cats

Answer 23

if the absolute reticulocyte count is greater than the reference interval when an animal is anemic, we classify it is a regenerative anemia

dogs: release very low numbers of reticulocytes in health, and will produce the most robust response of all common domestic species during regenerative anemia (so a mild reticulocytosis is normal to see in health)

cats: also release very low numbers in health, and will produce a good response to anemia; cats also have long lived punctate reticulocytes, meaning they stick around for a long time; so if see reticulocytosis, cat could have had anemia like two weeks ago, and also mild reticulocytosis can be expected in health

Question 24

explain the significance of increased nRBCs in peripheral blood

Answer 24

nRBCs can only be determined by a blood smear, as any analyzer will count them as a WBC

if increased is called rubricytosis and can have 2 types:

appropriate rubricytosis: indicative of intensely regenerative anemia but MUST have a concurrent robust reticulocytosis

inappropriate rubricytosis:
1. nRBCs without reticulocytosis
2. nRBCs are disproportionate to the regenerative response
can be due to either
1. spleen related: dysfunction or splenic disease, or post splenectomy
2. bone marrow disease and damage: often with neoplasia and heat stroke