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

The white-cell differential

15 min

Skills you'll build4 skills
  • Choose a suitable blood-film area and inspect the margins separately
  • Classify leukocytes from the features visible on a blood film
  • Recognize the usual adult proportions and absolute counts of each white-cell type
  • Calculate an absolute leukocyte-lineage count

At the bench: Classify cells and describe morphology in a manual differential

Try first

Try first

On low power, an otherwise well-spread film shows more leukocytes bunched at the side margins and feather edge than in the body of the film. Where do you count the 100-cell differential?

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.

Find the monolayer, then check the margins

The reliability of a differential depends on the area of the film where it is counted. At low power, survey the film and locate the usable counting area: the zone where red cells lie singly with minimal overlap and preserved central pallor.1 Large cells, clumps, and platelet aggregates collect at the feather edge and side margins, and red cells there lose their normal appearance.1 Count the 100-cell differential and evaluate routine red-cell morphology in the monolayer, then scan the margins and feather edge separately for platelet clumps and large abnormal cells.1

Classifying leukocytes

A leukocyte is identified from its nuclear shape, chromatin pattern, and cytoplasmic granules together. Size alone can mislead.4 A neutrophil shows a segmented nucleus with fine, pale granules. A small lymphocyte shows a dense, round nucleus and a thin rim of pale cytoplasm.4 A large reactive lymphocyte can approach a monocyte's size, and a blast with scant cytoplasm can be mistaken for a small lymphocyte. Classifying by size alone can skew the differential and miss a cell that needs referral.1

Absolute counts

The differential's categories share one total, so a change in one cell line changes the percentages of the others, even when their absolute counts are unchanged.2 Multiply each percentage by the total white-cell count to get that line's absolute count:

absolute count = percentage ÷ 100 × total WBC count

A white count of 3.0 × 10³/µL with 60% lymphocytes gives 1.8 × 10³/µL lymphocytes. The percentage looks high, but the absolute count is within the adult interval of 1.0 to 3.2 × 10³/µL.3 Report bands, metamyelocytes, and myelocytes by name so a left shift is visible in the report, and follow your laboratory's policy for including bands in the absolute neutrophil count.2

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. Clinical and Laboratory Standards Institute. Reference Leukocyte Differential Count (Proportional) and Evaluation of Instrumental Methods. CLSI document H20-Ed3. Wayne, PA: CLSI; 2026.
  3. American Society for Clinical Pathology Board of Certification. Medical Laboratory Scientist, MLS(ASCP) and MLS(ASCPi) Examination Content Guideline. Revised June 9, 2026. Accessed September 26, 2026. ASCP BOC examination content guideline
  4. College of American Pathologists. 2026 Hematology, Clinical Microscopy, and Body Fluids Glossary. 2026. Accessed September 26, 2026. https://www.cap.org/wp-content/uploads/documents/2026-Heme-Glossary-FINAL.pdf

Watch one

Read each decision and its explanation.

A CBC shows a WBC count of 6.4 × 10³/µL. The differential is 40% segmented neutrophils, 6% bands, 45% lymphocytes, 6% monocytes, 2% eosinophils, and 1% basophils. What is the absolute lymphocyte count, and does it fall within the adult reference interval of 1.0 to 3.2 × 10³/µL?

  1. Note the total WBC count, 6.4 × 10³/µL.

    Each percentage is applied to the total count.

  2. Convert the lymphocyte percentage to a fraction. 45% = 0.45.

    A percentage is the share of the total that one cell line contributes.

  3. Multiply: 0.45 × 6.4 × 10³/µL = 2.88 × 10³/µL.

    Multiplying the fraction by the total converts a share of the differential into a concentration in blood.

  4. Compare with the interval. 2.88 × 10³/µL is between 1.0 and 3.2 × 10³/µL.

    The absolute count is compared with the reference interval, because the percentage can mislead.

Report an absolute lymphocyte count of 2.88 × 10³/µL, within the adult reference interval.

Practice this skill

Your turn

Problem 1 of 3 · Hints available

A CBC shows a white blood cell (WBC) count of 12.0 × 10³/µL with 60% segmented neutrophils, 5% bands, and 3% metamyelocytes. Under an absolute neutrophil count (ANC) definition that includes segmented neutrophils and bands, what is the ANC?

Correct. (0.60 + 0.05) × 12.0 = 7.8 × 10³/µL. Metamyelocytes are reported by name, and the laboratory documents which cells its ANC includes so that serial results stay comparable.

Incorrect. 0.60 × 12.0 counts segmented neutrophils only and leaves out the bands the definition includes.

Incorrect. 0.68 × 12.0 adds the metamyelocytes, which are reported by name in their own category.

Hint
  1. Add the fractions your laboratory's ANC definition includes before multiplying.
  2. Multiply the combined fraction by the total WBC count.
  3. A category reported separately, such as metamyelocytes, is not included in the ANC unless the laboratory's definition includes it.

Review Left shift and marked reactive leukocytosis

Problem 2 of 3 · Hints available

A cell on the film is close to a monocyte in size, with a dense, round nucleus, clumped chromatin, and a thin rim of pale blue-gray cytoplasm. No cytoplasmic granules are visible, and the nucleus is not folded. How do you classify it?

A monocyte's nucleus is folded. This cell's nucleus is round and dense, so the cell is not classified by size.

Classified a cell from its size alone

A cell is classified from size, chromatin, nucleoli, and cytoplasm together. A large reactive lymphocyte called a monocyte for its size, or a blast called a lymphocyte for its scant cytoplasm, shifts the differential and can hide blasts that need referral.

A large reactive lymphocyte can approach a monocyte's size. The round, dense nucleus and thin cytoplasmic rim identify it as a lymphocyte.

Eosinophils show large orange-red granules and a usually bilobed nucleus. Neither feature is described here.

Hint
  1. Size is only one feature. Consider the nuclear shape and chromatin as well.
  2. A monocyte's nucleus is folded or indented. A round, dense nucleus points elsewhere.

Review Systematic microscopic film examination

Problem 3 of 3 · On your own

A WBC count of 4.2 × 10³/µL shows 68% segmented neutrophils and 20% lymphocytes. Using the adult intervals of 1.7 to 7.5 × 10³/µL for neutrophils and 1.0 to 3.2 × 10³/µL for lymphocytes, which lineage is outside its interval?

Percentages share one total, so a typical-looking percentage can still be outside the absolute interval. Multiply each percentage by the total before interpreting it.

Interpreted percentages without the total white-cell count

Differential percentages share one total, so a change in one cell type moves the others. At a WBC count of 3.0 × 10³/µL, 60% lymphocytes is 1.8 × 10³/µL, an absolute count within the reference interval, and the low absolute count is the neutrophil count. Reading the percentage alone reports the wrong lineage as abnormal.

0.68 × 4.2 = 2.86 × 10³/µL neutrophils, within 1.7 to 7.5 × 10³/µL. The neutrophils are not low.

0.20 × 4.2 = 0.84 × 10³/µL lymphocytes, below the 1.0 to 3.2 × 10³/µL interval. 0.68 × 4.2 = 2.86 × 10³/µL neutrophils, within 1.7 to 7.5 × 10³/µL.

Review White-cell parameters

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