Peripheral Blood Smear Differential Count: Workflow and Documentation

Before counting

Read the request, relevant analyzer output, and the laboratory’s validated smear-review criteria. The 2026 implementation paper discusses system, suspect, and numerical/definitive analyzer flags and delta checks as possible review triggers; criteria and workflow require local validation. [3] Barnes et al. (2005) is retained as historical consensus background, not a stand-alone current universal rule. [1]

In the founder’s practical review, marked abnormalities in WBC, RBC, or platelet counts or hemoglobin, increased immature cells, and other suspect populations can prompt manual review. These are practical categories, not numerical cutoffs; thresholds vary with analyzer and laboratory policy.

First inspect the stained film for adequacy and a representative region with preserved, distinguishable cells. Do not use a crowded, distorted, or otherwise unsuitable region simply to reach a target quickly.

Count systematically

A differential answers how the counted leukocytes were distributed among categories. A morphology review can add information about cell appearance, red cells, and platelets that the category percentages alone do not express. The ICSH recommends consistent terminology and grading for peripheral blood cell abnormalities. [2]

In the founder’s teaching approach, trainees first assess the whole smear at low power, select an adequately spread and well-preserved area, and avoid excessively thick, very thin, or distorted regions. They then move systematically through adjacent fields to avoid repeatedly examining the same area, while correlating the differential with RBC and platelet morphology. This is one teaching approach, not a single universally required navigation pattern.

1. Select the countable area according to the local procedure.
2. Follow a planned field progression and classify each eligible leukocyte once.
3. Record uncertain or potentially abnormal cells for the appropriate reviewer.
4. Check the category totals against the actual cells counted.
5. Report percentages with the denominator and any relevant limitation.

Documentation and common mistakes

A flagged analyzer result is a reason to follow the local review pathway, not a universal instruction that every film needs the same manual count. The person releasing a result must interpret it in the full laboratory and clinical context. A limited count should not be described as if the intended larger number of cells had actually been examined.

• State the specimen and actual count total, especially if the planned total could not be reached.
• If the intended total cannot be reached, state why, describe relevant specimen adequacy, and qualify the result for its limited denominator and reduced precision where appropriate.
• Record relevant morphology observations with accepted terms and the laboratory’s reporting convention.
• Avoid counting selected fields because they appear rich in a particular cell type.
• Do not substitute an automated flag or a digital tally for a qualified morphology decision.

Digital recording in this workflow

HemaSync can record the observer’s categories and actual total while the slide remains under professional review. It does not read the film, resolve uncertain cells, or validate the specimen. Voice-assisted entry should be checked against the visible tally before documentation.