03: CBC and Erythrocytes

Where do RBCs come from

Bone marrow

Quantitative CBC evaluations

Are there enough? Too much?

Qualitative CBC evaluations

Do they look normal?

Where do you get results for quantitative CBC values

Analyzer

Where do you get results for qualitative CBC values

Blood smear

What sorts of cases are you more likely to miss something if you don’t do a blood smear to check morphology

Clinically abnormal patients

Two methods a CBC analyzer uses

• Lytic dilution

• Isotonic dilution

Tests done in the lytic dilution

• [Hgb]

• WBC

How does the lytic dilution work

Burst red blood cells to release Hgb and leave WBCs intact

Tests done in the isotonic dilution

• RBC

• MCV

• Platelets

MCV

Mean cell volume; average size of an RBC

How do analyzers count cells

• Impedance method

• Flow cytometry

Difference between impedance method and flow cytometry for counting cells in a CBC

• Impedance method counts based on cell size as it interrupts an electrical current

• Flow cytometry counts based on cell size and some other characteristics using a laser and light scatter, more accurate

Big draw back of CBCs that use impedance methods for analyzers

Diseased cells may be a different size than normal, interfering with accuracy

Quantitative RBC tests

• RBC

• Hg

• HCT

Term for low RBCs

Anemia

Term for high RBCs

Erythrocytosis/Polycythemia

How are the RBC, Hgb, HCT related

They move together, unless something is abnormal with the RBCs

Manual way to measure RBC mass

PCV tubes

Conditions where you cannot use the RBC and HCT from an analyzer and you have to do a manual PCV

Patients with autoagglutination

List the 2 qualitative assessments of RBCs

• MCV

• MCHC

MCHC

How much Hg is in each RBC

Primary use of MCHC

Used as a quality control to see if there is an error in your sample

Terms for cells that are larger/smaller than normal

Macro/microcytic

Terms for cells that have too much/not enough Hg

Hyper/hypochromic

Causes of hyperchromia

Not a physiologic reality, because RBCs are normally stuffed with as much Hg as they can hold

Causes of hypochromia

• Low iron

• Bone marrow issues

Reticulocyte

RBCs that are so new to circulation that they still have mRNA

How long does it take for a reticulocyte to loose the mRNA and turn into a normal RBC

1-2 days

How are reticulocytes detected

Stained with vital dyes (like New Methylene Blue)

What is the name used for young RBCs if they are stained with Diff Quick

Polychromasia

Clinical use for reticulocytes

Informs if an anemia is regenerative or not (is the bone marrow responding?)

How do CBC analyzers detect reticulocytes

Fluorescence that tags any RNA in RBCs

How do you view cellular morphology changes

Blood smear!!!

Common RBC morphological change seen in IMHA

Spherocytes

Relative polycythemia

Increase in RBCs that will go back to normal

Common causes of relative polycythemia

• Dehydration artifact

• Splenic contraction

Common causes of absolute polycythemia

• RBC leukemia

• Chronic lung/heart disease → hypoxemia → more RBCs to compensate

Common cause of secondary anemia

Anemia of inflammatory disease

Basic mechanisms of anemia

• Hemorrhage

• Hemolysis

• Lack of production

First question you should ask when confronted with an anemia case

Regenerative or non-regen

Key indicator that an anemia is regenerative

Reticulocytes/polychromatophils

How do distinguish on a chem/CBC if a regenerative anemia is hemorrhage or hemolysis

Look at the total protein → hemorrhage will be losing whole blood, which is RBCs and total protein. Hemolysis will just be destroying RBCs

Causes of lack of production

• Intrinsic marrow disease

• Marrow suppression from outside the bone

How does the RBC population morphology change in a regenerative anemia

You will have a left shift, and the population will include reticulocytes/polychromatophils, and may include some late stage nucleated RBCs

Difference between reticulocytes and polychromatophils

• Reticulocytes are dyed with vital stains

• Polychromatophils are dyed with regular stains

Types of reticulocytes

• Aggregate (younger)

• Punctate (older)

T/F: bone marrow response mechanics are similar between species

HAH you wish

Which species won’t release reticulocytes into circulation even with a strong marrow response

Horses

How do you know if a horse has a regenerative anemia

You have to track the PCV over time

Three ways to evaluate a regenerative anemia

• Absolute reticulocyte count

• Polychromasia evaluation

• RBC indices

How is reticulocyte count and polychromasia evaluation different

• Retic count is an actual number, and the test is more sensitive

• Polychromasia is graded, and the test is less sensitive

T/F: polychromasia grading is the same across species

False; different species have different regenerative responses, so a response in a ruminant may be nothing for a dog

How do the RBC indices change in a regenerative anemia

• MCV will go up because reticulocytes are larger than mature RBCs (macrocytic)

• MCHC will go down because reticulocytes are not fully hemoglobinized (hypochromic)

How do the RBC indices compare with retic count for evaluating regenerative anemia

The RBC indices are pretty insensitive, because they measure mean changes. If there is a lot of RBCs, the affect of reticulocytes on the lab values will be tempered