Red cell shapes on a blood smear: spherocytes, schistocytes, Heinz bodies, acanthocytes

What it shows

• Spherocytes — small, dense, round red cells that have lost their pale centre. They form when macrophages bite off part of the membrane of antibody-coated cells.
• Schistocytes — fragments of red cells. They usually reflect mechanical injury: cells are sheared by damaged vessel walls, fibrin strands or turbulent flow. Cells made fragile by iron deficiency also break up.
• Heinz bodies — clumps of oxidised, precipitated haemoglobin inside the cell. Large ones are visible on the routine stain; small ones are easier to see with a special stain (new methylene blue). Cells with many Heinz bodies become rigid and are removed by the spleen.
• Acanthocytes — cells with a few irregular, blunt spikes of different lengths. They have to be told apart from echinocytes, which have regular, evenly spaced spikes; this can be difficult.

Higher than reference — what it may be a sign of

• Spherocytes — the main cause to consider is immune-mediated hemolytic anemia (IMHA). Moderate to marked numbers are regarded as diagnostic of IMHA. Lower numbers also occur with red cell fragmentation, oxidative injury, coral snake bites, bee stings and after a transfusion of stored blood.
• Schistocytes — conditions that damage vessels or blood flow: disseminated intravascular coagulation (DIC), kidney glomerular disease, vasculitis, a portosystemic shunt, haemangiosarcoma. Also iron deficiency.
• Heinz bodies — oxidative injury. Causes include onion and garlic, zinc (for example swallowed coins), paracetamol (acetaminophen) and some other drugs. After onion, Heinz bodies appear within 24 hours, and red cell breakdown typically follows 3–5 days after exposure.
• Acanthocytes — liver disease, fragmentation (DIC, iron deficiency) and cancer. In one study of 123 dogs with acanthocytes, 54% had cancer, most often haemangiosarcoma, osteosarcoma or lymphoma. Low numbers may not matter clinically.

The vet reads these findings together with the whole blood count. For example, many Heinz bodies in an anemic animal point to an oxidant, and the next step is looking for its source.

Lower than reference

“Not seen” is the usual result, but it does not rule things out. IMHA can occur with few spherocytes, and in cats spherocytes are hard to recognise at all. Small Heinz bodies can be missed on the routine stain. Smear reading is subjective: agreement between observers is poor at low spherocyte counts and better from about 5 per microscope field.

Look at together with

• Hematocrit and reticulocytes — is there anemia, and is the marrow responding.
• Coombs test — together with spherocytes and autoagglutination, it supports IMHA.
• Polychromasia — young red cells on the same smear.
• Platelets, D-dimer — when schistocytes raise the question of DIC.
• Iron — when schistocytes or acanthocytes appear with signs of iron deficiency.

Units and conversion

There are no units: these are descriptions of the smear. A common way to grade them is by eye as few, moderate or many. One grading scheme counts spherocytes per high-power microscope field: more than 5 per field is called moderate and more than 10 marked. Wording differs between labs; in the app the result is stored as text, as written on the form.

Reference range

The reference range is on your lab’s form. There is no number to compare against: the lab notes whether a change is seen and how much. In a healthy dog or cat these shapes are absent or rare, with known exceptions — a few spherocytes at the thin edge of many smears, and small Heinz bodies in healthy cats.

Cats and dogs

Sources

1. eClinPath (Cornell University College of Veterinary Medicine). Shape changes (poikilocytosis).
2. eClinPath (Cornell University College of Veterinary Medicine). Red blood cell inclusions — Heinz bodies.
3. eClinPath (Cornell University College of Veterinary Medicine). Red blood cells — quick guide.
4. Merck Veterinary Manual, professional version. Regenerative Anemias in Animals.
5. Merck Veterinary Manual, professional version. Garlic and Onion (Allium spp) Toxicosis in Animals.
6. Merck Veterinary Manual, professional version. Toxicoses From Human Analgesics in Animals.