Skip to content

Add your earlier progress to your account?

From before you signed in, this browser has:

Which plan do you want to keep?

You answered the plan questions before you signed in, and those answers don't match the plan saved on your account.

SettingSaved planNew answers

Study progress is waiting to be saved

Blasts on the film and cytochemistry

15 min

Skills you'll build3 skills
  • Recognize myeloblasts and Auer rods that call for an acute myeloid leukemia workup
  • Recognize lymphoblasts that call for an acute lymphoblastic leukemia workup
  • Match an MPO, Sudan black B, or esterase pattern to blast lineage

At the bench: Recognize abnormal cell findings that need further review

Try first

Try first

A film shows occasional blasts with fine chromatin, a nucleolus, and scant blue cytoplasm. The WBC count is 4.2 × 10³/µL, within the reference interval. What do you do?

Keep going to see the reasoning.

Right. Keep going to follow 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.

Blasts and Auer rods

Acute myeloid leukemia (AML) can present with a normal or low WBC count, and anemia, thrombocytopenia, and neutropenia can accompany few circulating blasts.1 A myeloblast has fine chromatin, one or more nucleoli, and scant blue cytoplasm. An Auer rod is a red, needle-shaped cytoplasmic inclusion that strengthens the finding when present.1 Dismissing blasts because the total count is not high delays the workup.

Lymphoblast size and morphology

Lymphoblasts fall into two size classes. The more common small form measures 1.0 to 2.5 times a normal lymphocyte, with scant blue cytoplasm and indistinct nucleoli. The larger form measures 2 to 3 times lymphocyte size, with a prominent nucleolus and an irregular nuclear membrane, and it can resemble a myeloblast.2 Reactive lymphocytes vary in size and chromatin pattern and have abundant cytoplasm. Calling a uniform blast population reactive delays the urgent workup. Morphology establishes that a blast process is present. Lineage and classification need immunophenotyping and genetics.2

Reading a cytochemical stain

Cytochemical stains support lineage when morphology is ambiguous, but a stain pattern cannot establish a disease entity.2 Myeloperoxidase (MPO) stains granulocytes and Auer rods strongly and monocytes weakly, and it does not stain lymphoid cells.2 Naphthol AS-D chloroacetate esterase, the specific esterase, marks granulocytic cells including Auer rods. α-Naphthyl acetate or butyrate esterase, the nonspecific esterase, shows strong diffuse positivity in monocytic cells, confirmed by inhibition with added sodium fluoride. Megakaryoblasts and lymphoblasts can show focal or dot positivity on the nonspecific esterase, so a reaction called monocytic without the fluoride-inhibition step can belong to a nonmonocytic lineage.2 A stain pattern supports a lineage. Classifying the leukemia requires immunophenotyping and genetic testing.2

Follow the bench demonstration

Sources for this step
References
  1. Arber DA, Borowitz MJ, Cessna M, et al. Initial diagnostic workup of acute leukemia: guideline from the College of American Pathologists and the American Society of Hematology. Arch Pathol Lab Med. 2017;141(10):1342-1393. doi:10.5858/arpa.2016-0504-CP
  2. 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

Watch one

Read each decision and its explanation.

A marrow film shows a blast population with strong diffuse cytoplasmic positivity on the α-naphthyl acetate esterase stain. How do you interpret this pattern?

  1. Describe the pattern. The positivity is strong and diffuse, as in monocytic cells. Megakaryoblasts and lymphoblasts typically show only focal or dot positivity.

    Nonspecific esterase can show focal positivity in nonmonocytic blasts, so the pattern is not conclusive without further testing.

  2. Run the fluoride-inhibition step. The reaction is markedly reduced with added sodium fluoride.

    Sodium fluoride inhibits the nonspecific esterase reaction in monocytic cells specifically, so it distinguishes a true monocytic reaction from one that only resembles it.

  3. Check MPO and the specific esterase on the same blasts. Both are negative.

    MPO and the specific esterase mark the granulocytic component of a mixed population, so checking them shows whether granulocytic cells are also present.

  4. Record the pattern as supporting monocytic differentiation, and refer the specimen for immunophenotyping and genetic testing to classify the leukemia.

    A stain pattern supports a lineage. Classifying the leukemia requires more than morphology and cytochemistry.

The fluoride-inhibited, diffusely positive nonspecific esterase with negative MPO and specific esterase supports monocytic differentiation. Immunophenotyping and genetic testing classify the leukemia.

Practice this skill

Your turn

Problem 1 of 3 · Hints available

A film shows abnormal promyelocytes packed with granules and cells with multiple Auer rods, and the same patient has thrombocytopenia with a low fibrinogen. What does the laboratory do?

Incorrect. Suspected acute promyelocytic leukemia is a medical emergency, so notification comes first, and rapid PML::RARA testing and coagulation studies proceed without waiting for the complete workup.

Incorrect. AML with PML::RARA has no fixed minimum blast percentage, and the urgency comes from the coagulopathy.

Correct. In suspected acute promyelocytic leukemia the coagulopathy can be severe, so abnormal promyelocytes or multiple Auer rods with thrombocytopenia, prolonged clotting times, low fibrinogen, or increased D-dimer call for immediate notification under your laboratory's urgent-result procedure.

Hint
  1. Look at the granules on the abnormal cells together with the coagulation findings.
  2. Acute promyelocytic leukemia has no fixed minimum blast percentage.
  3. The coagulopathy makes this urgent at any blast count.

Review Acute myeloid leukemia

Problem 2 of 3 · Hints available

A film from a child with fatigue and bruising shows a uniform population of small cells with round nuclei, indistinct nucleoli, and scant blue cytoplasm, all similar in size. What do you report?

Reactive lymphocytes vary in size and chromatin pattern and have abundant cytoplasm. This population is uniform, with fine chromatin and scant cytoplasm.

Counted lymphoblasts as reactive lymphocytes

Lymphoblasts have fine chromatin, a high nucleus-to-cytoplasm ratio, and scant blue cytoplasm, with nucleoli in the larger form, and similar cells repeat across the film. Reactive lymphocytes vary in size and chromatin and have abundant cytoplasm. Calling a blast population reactive delays the urgent acute-leukemia workup.

Fine chromatin, a high nucleus-to-cytoplasm ratio, and scant blue cytoplasm in a uniform population across the film are features of lymphoblasts. The finding calls for urgent referral.

Normal small lymphocytes have dark, condensed chromatin. This population's fine chromatin and indistinct nucleoli are features of a lymphoblast.

Hint
  1. Compare this population with the variation expected in reactive lymphocytes.
  2. A uniform population of similar cells across the film is a significant finding.

Review Morphology and immunophenotype

Problem 3 of 3 · On your own

A different blast population shows strong diffuse α-naphthyl acetate esterase positivity. No fluoride-inhibition step was run. What do you do before reporting a lineage?

A strong diffuse pattern requires the fluoride-inhibition step. Without it, a nonmonocytic reaction can be called monocytic.

Called esterase positivity monocytic without fluoride

Monocytic cells show strong diffuse nonspecific esterase that sodium fluoride inhibits. Megakaryoblasts and lymphoblasts can show focal or dot positivity. Without the inhibition step, a nonmonocytic reaction can be called monocytic. Cytochemistry supports a lineage, and classifying the leukemia needs immunophenotyping and genetic testing.

Monocytic cells show strong diffuse nonspecific esterase that sodium fluoride inhibits. The inhibition step confirms the lineage the pattern suggests.

The stain can be interpreted once the inhibition step is added. Fluoride inhibition confirms or excludes the monocytic reaction that the uninhibited stain suggests.

Review Special stains

Use it

Use the specimen and readings to make the next bench decision. The step is complete without it.

Try this at the MicroscopeWBC0 / 100MANUAL DIFF ORDEREDPeripheral blood differentialPerform manual diff

For reference

Sources checked