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Red-cell shapes on the film

14 min

Skills you'll build4 skills
  • Recognize the central staining pattern of a target cell
  • Distinguish echinocyte projections from acanthocyte projections
  • Recognize schistocytes and the percentage that suggests thrombotic microangiopathy
  • Recognize a Howell-Jolly body as a nuclear remnant

At the bench: Relate red cell indices and morphology to the anemia workup

Try first

Try first

A red cell in the monolayer shows a dark center surrounded by a pale ring, with a darker rim at the very edge, like a target on a dartboard. What is this called?

Right. Keep going to follow the reasoning.

Keep going to see the reasoning.

Keep going to see the reasoning.

Keep going to see the reasoning.

Get the idea

Use the explanation to check your first decision.

Assessing red-cell shape

Red-cell evaluation covers size, hemoglobinization, shape, inclusions, and arrangement, and each poikilocyte is assessed in the monolayer, where cells lie singly and normal cells keep their pallor.1 A target cell (codocyte) shows a central puddle of hemoglobin from excess membrane relative to volume, seen with liver disease, Hb C disease, thalassemia, and after splenectomy.1

Echinocytes and acanthocytes

Echinocytes have short, evenly spaced spicules, usually a drying or pH artifact, and also occur in uremia and pyruvate kinase deficiency. Acanthocytes have irregular, unevenly spaced projections of unequal length, with no central pallor, and suggest severe liver disease (spur cell anemia) or abetalipoproteinemia.1 The regularity of the spacing around the cell distinguishes them.

Schistocyte counts and thresholds

Schistocytes are fragments with sharp angles, straight borders, helmet forms, or small crescents. The International Council for Standardization in Haematology (ICSH) treats a count above 1% as suspicious for thrombotic microangiopathy in adults and full-term neonates, when fragments are the main red-cell abnormality and a validated counting method is used.2 Counts at or below 1% occur in healthy adults and with mechanical devices, dialysis, and renal disease, so the film result is interpreted with the platelet count and hemolysis markers.2

Howell-Jolly bodies

A Howell-Jolly body is a single, round, dense purple nuclear remnant, usually one per cell, seen after splenectomy, with hyposplenism, and in megaloblastic anemia. Pappenheimer bodies are small clustered granules that need a Prussian blue stain to confirm. A persistent Howell-Jolly body points to reduced splenic function or megaloblastic change and is unrelated to iron.1

Follow the bench demonstration

Sources for this step
References
  1. Keohane EM, Preston MM, Mirza KM, Walenga JM, eds. Rodak's Hematology: Clinical Principles and Applications. 7th ed. Elsevier; 2025. Accessed September 26, 2026. https://www.us.elsevierhealth.com/rodaks-hematology-9780323936507.html
  2. Zini G, d'Onofrio G, Erber WN, et al. 2021 update of the 2012 ICSH recommendations for identification, diagnostic value, and quantitation of schistocytes: impact and revisions. Int J Lab Hematol. 2021;43(6):1264-1271. doi:10.1111/ijlh.13682

Watch one

Read each decision and its explanation.

A film review is requested after a report of a falling platelet count and a rising creatinine. Screen the film for schistocytes.

  1. Scan at low power for overall red-cell shape abnormalities.

    Low power shows the overall pattern and confirms the film quality before closer review.

  2. Move to the monolayer and look for cells with sharp angles, straight borders, helmet, or crescent shapes.

    Schistocytes are assessed where cells lie singly and normal cells keep their pallor.

  3. Count the schistocytes in the monolayer: 30 of 1,000 red cells, or 3.0%.

    The threshold is a percentage, so a count is needed. The ICSH method counts schistocytes among at least 1,000 red cells.

  4. Compare with the other findings. The platelet count is falling and creatinine is rising, with a schistocyte count above the 1% threshold.

    The film result is interpreted with the platelet count and hemolysis markers.

Report schistocytes at 3%, above the 1% threshold. Communicate the pattern promptly, because with the falling platelets and rising creatinine it is suspicious for thrombotic microangiopathy.

Practice this skill

Your turn

Problem 1 of 3 · Hints available

On an appropriate film area, which feature favors an echinocyte over an acanthocyte?

Correct. Echinocyte projections are regular. Acanthocyte projections are irregular in size and spacing. Consider artifact when echinocytes are present.

Incorrect. That description favors an acanthocyte.

Incorrect. That is the characteristic target-cell pattern.

Hint
  1. Compare the spacing of the projections around the cell.
  2. One type of spicule is usually an artifact of drying or pH.

Review Red-cell morphology on the stained film

Problem 2 of 3 · Hints available

A schistocyte count of 3% is reported on a patient with a normal platelet count and no other abnormal finding. A colleague says this alone proves thrombotic microangiopathy. What is the correct interpretation?

A count above 1% raises suspicion for thrombotic microangiopathy. The platelet count, hemolysis markers, and coagulation results are interpreted with it before that cause is assigned.

Attributed schistocytes to one cause without other findings

Helmet and triangular fragments point to mechanical or microangiopathic injury, and ICSH treats more than 1% schistocytes as suspicious for thrombotic microangiopathy in adults. The platelet count, hemolysis markers, coagulation results, and ADAMTS13 activity then separate TTP, HUS, DIC, and device injury.

A normal platelet count and no other abnormal finding argue against an acute thrombotic microangiopathy. The film result is one part of the whole pattern.

The ICSH threshold for suspicion is a count above 1%. The count is interpreted with the rest of the findings.

Hint
  1. A count above 1% is described only as suspicious for thrombotic microangiopathy.
  2. Check what the platelet count and hemolysis markers add to the film result.

Review Red-cell morphology on the stained film

Problem 3 of 3 · On your own

A film shows a single, round, dense purple inclusion in one red cell. A few other cells show small, dust-like clustered granules that stain positive with Prussian blue on a follow-up stain. Which inclusion is the Howell-Jolly body?

A Howell-Jolly body is usually a single, round, dense purple nuclear remnant, one per cell.

Small clustered granules that stain with Prussian blue are Pappenheimer bodies, which contain iron. A Howell-Jolly body is a single dense nuclear remnant and does not stain with Prussian blue.

Called a Howell-Jolly body an iron granule

A Howell-Jolly body is usually a single round, dense purple nuclear remnant. Pappenheimer bodies are small clustered granules that stain with Prussian blue. Persistent Howell-Jolly bodies point to reduced splenic function or megaloblastic change, and calling them iron misses that finding.

These are two distinct inclusions with different compositions: a nuclear remnant in one case and iron-containing granules in the other.

Review Red-cell morphology on the stained film

Use it

Read the case evidence, then make each decision. The step is complete without it.

  • A man, MRN 0455812, 3 weeks after mechanical aortic valve replacement, reports fatigue.
  • His hemoglobin has fallen since his last visit.
  • The monolayer shows red cells with sharp angles and helmet shapes.
  • A few cells show a central hemoglobin puddle surrounded by pallor.
  • One red cell contains a single, round, dense purple inclusion.
  • He has no history of splenectomy, liver disease, or megaloblastic anemia.
TestResultPreviousReference intervalFlag
Hemoglobin10.8 g/dL Low6 weeks ago: 13.6 g/dL13.6 g/dL6 weeks ago13.5–17.5 g/dL13.5–17.5Low
Platelet count210 × 10³/µL6 weeks ago: 230 × 10³/µL230 × 10³/µL6 weeks ago150–400 × 10³/µL150–400

Specimen: H 4, L 6, I 1. EDTA whole blood

Decision 1 of 3

You count schistocytes in the monolayer: 50 among 1,000 red cells, or 5.0%. What do you do next, following the laboratory's procedure for a result above the reporting threshold?

A count above the 1% threshold is reported and communicated under the laboratory's procedure, together with the clinical setting of a mechanical valve.

A count above the reporting threshold is acted on when it is found.

The film finding is reported when it is found. The platelet count is interpreted with it but does not determine whether the finding is reported.

Review Red-cell morphology on the stained film

Decision 2 of 3

Separate from the fragmented cells, a few cells show a central hemoglobin puddle surrounded by pallor. No liver disease or thalassemia is documented, and his spleen is intact. What do you report?

Target cells reflect excess membrane relative to volume and are nonspecific. They are reported as observed and correlated with the clinical picture, which here does not yet explain them.

A spherocyte lacks central pallor entirely and looks dense throughout. A central puddle with surrounding pallor is the target-cell pattern.

Schistocytes are angular fragments with sharp borders. A central puddle of hemoglobin describes the target-cell pattern, a different shape reported separately.

Review Red-cell morphology on the stained film

Decision 3 of 3

One red cell contains a single, dense, round purple inclusion. His spleen is intact, and there is no history of megaloblastic anemia. What do you do with this finding?

A single, round, dense purple nuclear remnant is a Howell-Jolly body. It is reported as seen, and the clinical team relates it to his history.

A single dense purple inclusion matches a Howell-Jolly body. A Pappenheimer body needs a Prussian blue stain to confirm its iron, and no stain was done.

Called a Howell-Jolly body an iron granule

A Howell-Jolly body is usually a single round, dense purple nuclear remnant. Pappenheimer bodies are small clustered granules that stain with Prussian blue. Persistent Howell-Jolly bodies point to reduced splenic function or megaloblastic change, and calling them iron misses that finding.

A single round, dense inclusion inside the cell matches a Howell-Jolly body. It is reported as observed.

Review Red-cell morphology on the stained film

The man with a new mechanical valve has a schistocyte count of 5.0%, above the 1% threshold. Red-cell fragmentation at the valve fits both the count and the falling hemoglobin. The target cells and the single Howell-Jolly body are reported as separate findings.

For reference