SCV 213: Lecture 3 RBC

What is hematopoiesis?

Production of blood cells and platelets

• erythropoiesis (RBCs)

• leukopoiesis (WBCs)

• thrombopoiesis (platelets)

Where does hematopoiesis happen?

• Before birth: liver, spleen, thymus, and bone marrow

• Adults: mainly in the red bone marrow, but the liver and spleen can pick it back up if the body is under stress.

What is erythropoietin (EPO) and what does it do?

It's a cytokine made by the kidneys when blood oxygen levels drop. It travels to the bone marrow and binds to erythroid precursor cells, telling them to divide and mature into RBCs.

What is the basic job and structure of a red blood cell?

RBCs carry oxygen using hemoglobin, which has an iron-containing heme portion and a protein globin portion. In adult mammals, RBCs lose their nucleus and typically have a biconcave disc shape.

How does RBC shape differ between species?

Dogs have a biconcave disc with a pale center, cats are rounder with little to no pale center, and birds/reptiles/fish keep a nucleus with an oval shape. Llamas and camelids have elongated, oval-shaped RBCs.

What is the order of RBC development stages?

Rubriblast, prorubricyte, basophilic rubricyte, polychromatophilic rubricyte, metarubricyte, reticulocyte, then mature erythrocyte. The whole process takes about 2 days.

What does the Rubriblast look like and why?

It's the earliest and largest stage, with a big nucleus containing a nucleolus for making ribosomes, and dark blue (basophilic) cytoplasm. The deep blue color comes from all the RNA needed to build hemoglobin.

What happens during the three rubricyte stages?

The prorubricyte loses its nucleolus, the basophilic rubricyte's cytoplasm starts lightening with a clumpier nucleus, and the polychromatophilic rubricyte turns lavender as hemoglobin builds up and RNA need drops.

What's special about the Metarubricyte stage?

The cell is much smaller with deep red cytoplasm, since hemoglobin synthesis is now complete. Its nucleus is fully condensed (pyknotic), and the cell can no longer divide.

What is a reticulocyte?

It's an immature RBC that has lost its nucleus but still has leftover RNA remnants, giving it a lavender color. It's bigger than a mature RBC and may show up in blood in higher numbers when the body is responding to anemia.

What defines a mature erythrocyte in mammals?

It's lost its nucleus completely and has little to no RNA left, leaving an all-red cell built for carrying oxygen. Lifespan ranges from about 1 to 6 months depending on species.

What does a CBC (Complete Blood Count) include?

Total RBC count, PCV, plasma protein, total WBC count, a blood film exam (WBC differential and cell morphology), reticulocyte count, hemoglobin concentration, and erythrocyte indices.

Why are manual cell counts rarely done in general practice anymore?

Automated analyzers do it faster, and RBCs number in the millions, making manual counting impractical. Manual counts are mostly reserved for avian/exotic patients, zoos, or some international settings.

What is PCV (Packed Cell Volume) and how is it measured?

It's the percentage of whole blood made up of RBCs. Anticoagulated blood is spun in a microhematocrit centrifuge, and you should always fill more than one tube since they break easily.

What three layers form after spinning a PCV tube?

RBCs at the bottom, a buffy coat of WBCs and platelets in the middle (its height roughly estimates WBC count), and plasma on top. Plasma color should also be checked, since normal is clear to pale yellow.

Why do we bother running a PCV if it's so simple?

It's a fast screening tool for conditions like anemia, polycythemia, dehydration, and acute hemorrhagic diarrhea syndrome. A quick spin gives a lot of diagnostic info for very little effort.

What does a low PCV usually mean?

It usually points to anemia, or sometimes just an improper blood-to-anticoagulant ratio in the tube. Low PCV is under 37% in dogs and under 30% in cats.

What does a high PCV usually mean?

It can mean polycythemia or dehydration, since less fluid in the vessels concentrates the RBCs. High PCV is over 55% in dogs and over 45% in cats.

What's the difference between regenerative and non-regenerative anemia?

Regenerative anemia means the bone marrow is responding by making more RBCs to fix the problem. Non-regenerative means the bone marrow isn't responding at all.

What are the three general causes of anemia?

Decreased RBC production, increased RBC loss, or RBC destruction.

What's the difference between relative and absolute polycythemia?

Relative polycythemia is usually temporary, often from splenic contraction during stress or dehydration. Absolute polycythemia is a real increase in RBCs, either primary (a bone marrow disorder) or secondary (from another condition raising EPO, like kidney disease).

How is plasma protein (total protein) measured as part of a CBC workup?

It's read off a spun hematocrit tube using a refractometer, even though it's technically a chemistry test. A lipemic sample can falsely raise this reading due to fat particles (chylomicrons) in the blood.

How is hemoglobin concentration measured?

It can be read directly with a hemoglobinometer, estimated by an automated analyzer, or roughly calculated by dividing PCV by 3.

What does MCV (Mean Corpuscular Volume) measure and how is it calculated?

It measures the average size of RBCs. Formula: PCV divided by RBC count, times 10, giving a result in femtoliters (fL).

What does MCH (Mean Corpuscular Hemoglobin) measure and how is it calculated?

It measures the average weight of hemoglobin in each RBC. Formula: hemoglobin concentration divided by RBC count, times 10, giving a result in picograms (pg).

What does MCHC (Mean Corpuscular Hemoglobin Concentration) measure and how is it calculated?

It measures the concentration of hemoglobin inside the average RBC. Formula: hemoglobin concentration divided by PCV, times 100, giving a result in g/dL.

How are anemias classified by MCV (size)?

Normocytic means average-sized RBCs, macrocytic means bigger RBCs (often from a regenerative response), and microcytic means smaller RBCs (often from iron deficiency).

How are anemias classified by MCHC (hemoglobin concentration)?

Hypochromic means low hemoglobin concentration (often iron deficiency), and normochromic means a normal level. True hyperchromic isn't really possible, since RBCs have a fixed hemoglobin capacity.

Why is a peripheral blood smear still necessary even with an automated analyzer?

It lets you do a WBC differential, estimate platelets, check RBC/WBC shape, and spot blood parasites. Automated machines can't assess cell morphology, so a smear catches what they'd miss.

What are the three stages of Diff-Quik staining?

A fixative (light blue, methanol) that sticks cells to the slide, eosin (red, acidic) that stains basic cell components like hemoglobin, and methylene blue (deep blue, alkaline) that stains acidic components like nuclei.

How are morphologic changes on a blood smear graded?

Using either a numeric scale (1+ to 4+) or a word scale (slight, mild, moderate, marked), both estimating roughly what percentage of cells show the change.

What is Rouleaux?

RBCs stack together like a roll of coins due to their flat, disc shape. It's normal in healthy horses, and to some extent cats and pigs, but abnormal in dogs, and can also just be an artifact of a sample sitting too long.

What is autoagglutination and how is it different from Rouleaux?

It's when antibodies coat RBCs and cause them to clump together, seen in immune conditions like IMHA. Unlike Rouleaux, a drop of saline won't separate the cells since they're truly stuck together, not just stacked.

What is anisocytosis?

It's variation in RBC size within the same sample, some bigger (macrocytes) and some smaller (microcytes). It's seen with regenerative or immune-mediated anemias and iron deficiency, but is actually normal in healthy cattle.

What is polychromasia?

It's a bluish tint on young, immature RBCs released early from the bone marrow, caused by leftover RNA mixing with red hemoglobin. A few of these (polychromatophils) can be normal in dogs.

What is hypochromasia?

It's RBCs that look paler than normal due to not enough hemoglobin inside them, usually from iron deficiency. It often shows up alongside microcytosis and a low MCHC.

What are Echinocytes (Burr cells)?

RBCs with small, even, evenly-spaced spikes all over the surface. Usually just an artifact from a slow-drying or old sample, but can also come from snake bites, burns, or kidney failure.

What are Acanthocytes (Spur cells)?

RBCs with irregular, unevenly-spaced spikes. Usually linked to abnormal fat metabolism, but also seen with hemangiosarcoma, iron deficiency, and liver disease.

What are Schistocytes?

Fragments of RBCs broken apart by trauma or shearing inside blood vessels. Seen with conditions like DIC or hemangiosarcoma.

What are Spherocytes?

RBCs that are sphere-shaped instead of the normal biconcave disc, with no central pale area. Commonly linked to immune-mediated destruction of RBCs, like IMHA or a transfusion reaction.

What are Howell-Jolly bodies?

Small, round, dark purple leftover nuclear bits inside young RBCs that didn't get fully cleared out. Normally the spleen removes these, so they show up more in post-splenectomy patients, though a few can be normal in cats and horses.

What are Heinz bodies?

Small round spots of damaged hemoglobin stuck to the outside of the cell membrane. They point to oxidative damage, often from a toxin or drug reaction, though a few can be normal in cats.

What is basophilic stippling?

Small dark-blue dots inside the RBC from clumped leftover RNA. Seen in immature RBCs responding to anemia in ruminants, and also associated with lead poisoning.

What are nucleated RBCs (nRBCs) on a smear?

They're very immature RBCs that still have their nucleus, released too early from the bone marrow, usually during anemia. They're a normal finding in non-mammals like birds and reptiles.

What is Mycoplasma spp. (on a blood smear)?

Small blue bacteria that sit on the outside surface of RBCs. It causes feline infectious anemia, also called hemobartonella.

What is Babesia spp.?

A large, teardrop-shaped protozoan parasite that lives inside RBCs, spread by ticks. It causes hemolytic anemia or clotting problems in dogs, cattle, and horses.

What is Cytauxzoon felis?

A small, ring-shaped protozoan parasite inside feline RBCs, spread by ticks. It's often fatal in cats, and the bobcat acts as its reservoir host.

What are the two main types of automated hematology analyzers?

Electrical impedance analyzers and laser-based flow cytometry analyzers. Both count and sort RBCs, WBCs, and platelets, which is called cytometry.

What are the benefits and downsides of automated analyzers?

Benefits: cost-effective, fast, convenient for running multiple tests a day. Downsides: they can't evaluate cell shape (morphology), and clumped platelets can throw off the count.

How does an electrical impedance analyzer work?

Blood passes single-file through a tiny opening between two electrodes. Since cells block the electrical current as they pass, the amount of disruption tells the machine the cell's size, giving a count and volume.

How does a laser-based flow cytometry analyzer work?

Blood cells pass single-file through a focused laser beam, and the way light scatters off each cell depends on its size, density, and whether it has granules or a nucleus. That scatter pattern is used to identify and count each cell type.