Answering your questions

A Body fluids contain a
number of cell types, nucleated and non-nucleated cells (red blood cells).
The nucleated cells include hematopoietic and non-hematopoietic cells. The
hematopoietic cells are comprised of nucleated red blood cells, lymphocytes,
monocytes, and neutrophils. The non-hematopoietic cells include mesothelial
cells and histiocytes/macrophages. A third group of nucleated cells is the
malignant cells, which originate from hematopoietic cells (lymphoma cells or
leukemia blasts) or non-hematopoietic metastatic-tumor cells (carcinoma,
melanoma, sarcoma, and so forth).

The atypical cells are counted only when they are discernible as
single cells and they can be described morphologically in a concise way.

Body-fluid cell counts are usually performed manually
in a hemocytometer, when the cell numbers and/or sample volume are deemed
too small for automated analysis. These non-stained counts yield an absolute
cell count and the ratio of nucleated to non-nucleated cells. Afterwards a
cytospin slide is stained and reviewed to obtain a differential count of 100
cells. We include hematopoietic (lymphocytes, monocytes, neutrophils, etc.)^l
and non-hematopoietic nucleated cells (mesothelial cells, macrophages, and
so forth) in the differential. Another category that is included in the
differential count is called “atypical cells.” The atypical cells could be
blasts, lymphoma cells, and other metastatic tumor cells. The atypical cells
are counted only when they are discernible as single cells and they can be
described morphologically in a concise way. Large groups or clusters of
atypical cells are not included in the differential and reported separately.
All cases with atypical cells should be sent for pathologist review if there
is no previous diagnosis pertaining to the findings.

Methods and principal cell types can be found in the
Clinical and Laboratory Standards Institute (CLSI) Guideline: Body Fluid
Analysis for Cellular Composition.¹

—Winfried Reichelt, MD,
PhD

—Eric Nutt, MT(ASCP)

—Guang Fan, MD, PhD

Oregon Health and Science University

Portland, OR

Reference

1. Clinical and Laboratory Standards Institute.
   Body Fluid Analysis for Cellular Composition; Proposed
   Guideline, CLSI Document H56-P, August 2005

Brad S. Karon, MD, PhD, is assistant professor of
laboratory medicine and pathology, and director of the Hospital Clinical
Laboratories, point-of-care testing, and phlebotomy services at Mayo
Clinic in Rochester, MN. Dr. Karon was selected by Daniel M. Baer, MD,
as his replacement. Dr. Baer, who died on April 5, 2009, was editor of
this column for 25 years.