Skip to content
SearchProgress
Display

Display

Theme
Density
Text size

Sign in

Add your earlier progress to your account?

Study progress is waiting to be saved

The white-cell differential

15 min

  • 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

Read the full reference

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 read the 100-cell differential?

The next section explains it.

Right. The next section explains why.

The next section explains it.

The next section explains it.

Get the idea

Find the monolayer, then check the margins

A differential is only as reliable as the area of the film it is read from. 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 read routine red-cell morphology in the monolayer, then scan the margins and feather edge separately for platelet clumps and large abnormal cells.1

Classify each cell from more than one feature

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, so size alone shifts the differential and can hide a cell that needs referral.1

Turn percentages into absolute counts

The differential's categories share one total, so a change in one line moves the percentages of the others even when nothing else changed.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, and the absolute count sits inside the adult interval of 1.0 to 3.2 × 10³/µL.3 Report bands, metamyelocytes, and myelocytes by name so a left shift stays visible, and follow your laboratory's policy for including bands in the absolute neutrophil count.2

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

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. Read the total WBC count: 6.4 × 10³/µL.

    Percentages are read against the total count as a whole.

  2. Take the lymphocyte fraction: 45% = 0.45.

    A percentage is the share of the total that one 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 falls between 1.0 and 3.2 × 10³/µL.

    The reference interval is compared against the absolute count, since the percentage alone can mislead.

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

Your turn

Problem 1 of 3

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 by name, such as metamyelocytes, stays out of the ANC unless the definition names it too.

Review Left shift and marked reactive leukocytosis

Problem 2 of 3

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 size alone does not settle the classification.

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 place it with the lymphocytes.

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

Hint
  1. Size is one clue among several. Weigh the nuclear shape and chromatin as well.
  2. A monocyte's nucleus is folded or indented. A round, dense nucleus points elsewhere.

Review Immune cells and laboratory identification

Problem 3 of 3

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 sit on either side of the absolute interval. Multiply each percentage by the total before judging 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. The neutrophils are the low lineage. 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

Try this at the MicroscopePendingWBC0 / 100PENDINGPeripheral blood differentialPerform manual diff

Keep

Sources checked