Q&A column

Editor: Frederick L. Kiechle, MD, PhD

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Q. When reviewing a smear, we observed scattered (rare) immature granulocytes during a scan. But when the 100-cell differential was performed, the immature granulocytes were not reflected. How do you report the presence of the immature granulocytes?

A. December 2019—The immature granulocyte (IG) fraction—metamyelocytes, myelocytes, and promyelocytes—can be quantified on modern peripheral blood analyzers as part of the six-part automated differential of the white blood cell count. The total number of cells counted for differentials is, of course, much higher by automated methods (30,000 cells on Sysmex platforms, for example) compared with a manual method (standardly 100 cells).

Therefore, as noted in the question, a low proportion of IGs detected by automated differential may not be reflected in a random 100-cell manual differential. This discrepancy may occur not only because of significant differences in the total cell count but also because of other factors affecting the peripheral blood smear. For example, immature cells, because of their relatively large size, tend to concentrate at the feathered edge, so their distribution may be less random across a slide than in a fluid state.

One strategy used by our hospital-based laboratory to address rare IGs is to add a white blood cell morphology comment to the manual differential of “slight left shift.” This signals that immature granulocytes are present but that they represent less than one percent of WBCs—that is, less than one cell per 100 on a standard manual differential. A parenthetical or footnoted statement with this additional information could also be included.

A related strategy is to avoid manual review for low IG fractions alone when using analyzers that produce an IG count. (With analyzers that only generate a flag that IGs are present, manual review is always recommended.) Recent studies highlight the accuracy of modern analyzers in identifying IGs and advocate for reflex release of these automated values without a flag for manual review at low IG fractions (less than three percent to less than 10 percent, as suggested by varying sources). Automated IG fractions may be overestimated due to a systematic positive error, and flag for manual review is appropriate at high proportions, regardless of whether the analyzer quantifies IGs. On the other hand, there is significant interobserver variability in manually distinguishing between metamyelocytes and band neutrophils, with the latter best included in the neutrophil fraction and not separately reported, and less so by automated methods.

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Bourne S, Ma N, Gulati G, Florea AD, Gong J. Evaluation of automated versus manual immature granulocyte counts. Lab Med. 2013;44(3):282–287.

Chabot-Richards DS, George TI. White blood cell counts: reference methodology. Clin Lab Med. 2015;35:11–24.
Eilertsen H, Hagve TA. Do the flags related to immature granulocytes reported by the Sysmex XE-5000 warrant a microscopic slide review? Am J Clin Pathol. 2014;142(4):553–560.

MacQueen BC, Christensen RD, Yoder BA, et al. Comparing automated vs manual leukocyte differential counts for quantifying the ‘left shift’ in the blood of neonates. J Perinatol. 2016;36(10):843–848.

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Alexandra E. Kovach, MD
Assistant Professor of Pathology,
Microbiology, and Immunology
Vanderbilt University Medical Center
Nashville, Tenn.
Member, CAP Hematology/Clinical
Microscopy Committee