Leukocytes or white blood cells designate all the hemoglobin
free blood cells. These cells belong to the reticuloendothelial
system. Based on their nuclear aspect, white blood cells can be
divided into two categories: mononuclear cells and polynuclear
cells. Lymphocytes and monocytes are the principal mononuclear
cells and polynuclear are subdivided into neutrophilic,
eosinophilic and basophilic cells. In the urinary sediment, the
term leukocyte is usually interpreted as polynuclear, mostly
neutrophils. The reason for this situation is that the
neutrophils are, by far, the most abundant leukocytes in urine.
In a normal specimen, up to 6 or 7 neutrophils / high-power field
can be observed. High neutrophil counts are usually related to an
Mononuclear leukocytes are occasionally seen. High mononuclear
counts are usually related to a high blood count pathology,
infiltrating the urinary space.
Under bright field microscopy and without staining,
identification of the different types of white blood cells is
almost impossible. The term leukocytes is indicated for the
routine microscopy. The subclasses of leukocytes can be
identified by staining with the Wright or PAP stain. Efficiency
of these staining procedures is highly dependent of the
conservation state of the cells. Staining with these represents a
workload, not justified for the routine specimen.
A polynuclear neutrophil (neutro) is a plurilobular nucleus
bearing cell with a slightly granulated cytoplasm. Neutros have
two types of granulations (lysozome) named azurophilic and
specific. Neutros lysozomes havediverse enzyme activities, some
being specific like the peroxydase. Neutrophils also possess a
heterogenic group of hydrolase gathered under the term esterase.
One of these esterases, the Naphtyl AS-D
Chloroacetate esterase, seems to be specific for the
polynuclear lineage. This activity is shared with the mastocytes
and some macrophages (some think that this activity is due to
phagocyted neutros). Since mastocytes are not seen in urine, and
that the macrophage size and aspect is quite different from
leukocytes, this activity is used in a specific staining
procedure for leukocytes.
Because of a pycnotic nucleus or of an unfavorable refractive
index of the urine, the plurilobulated nucleus are not always
obvious. Acidification of the sediment, with one drop of 2%
acetic acid enhances the contrast of the preparation.
| In the urinary sediment,
there are two types of neutrophils. The first type is the
usual named "Old" by Stamey. When
numerous, these cells are related to inflammation.
| The second type, named
"Fresh" by Stamey, and "Pale cells"
by Sternheimer, is bigger in size and resistant to some
stains. If the urine density is lower than 1,019 this
cell will demonstrate a brownian movement of its granules
wich will give a glittering cytoplasm. These cells are
then called glitter cells. For a time, these cells were
thought to be specific to pyelonephritis. Since these
were found in other conditions the accepted
interpretation is relating them to an active inflammation
process of the urinary tract.
characteristic of the activated neutrophil is it's adherent
capacity. This characteristic is essential for the migration of
the cell. Because of this, neutrophils can easily aggregate. In
some cases, it is important not to confuse cell aggregation and
pus. Pus is formed of degenerated neutrophils (pyocytes) and
cellular debris compacted into a mass where cell identity is
lost. This discrimination is not commonly used with the urinary
sediment, so that many aggregates are reported as pus. The term
pus should be restrained to real pus.
This cell is different from the other polynuclear cells
because of the affinity of its granules for the acid stains like
eosin. To be able to distinguish this cell, it is absolutely
necessary to stain. In a comparative study, by Nolan and Kelleher, the former has
shown that the Hansel stain was
superior to the Wright stain for eosinophiluria. The presence of
urinary eosinophils is a useful indicator of acute allergic
interstitial nephritis. Eosinophiluria is also seen in conditions
other than nephritis.
Causes of eosinophiluria
|Acute allergic interstitial nephritis
|Rapidly progressive glomerulonephritis
|IgA nephropathy, Henoch-Schönlein
|Graft rejection (acute phase)
Lymphocytes can occasionally be seen in a normal sediment.
High counts have been reported in cases of acute allergic
interstitial nephritis, rapidly evolutive glomerulonephritis, and
With bright field microscopy, the cell cannot be
differentiated from the usual leukocytes. With the PAP stain, the
cell is small, as a round nucleus with little cytoplasm.
In a study using monoclonal antibodies, a high number of
urinary monocytes has been reported in cases of acute allergic
interstitial nephritis and of rapidly evolutive
glomerulonephritis. In necrosis, these were rare or absent.
Like the lymphocytes, monocytes cannot be identified with
bright field microscopy. With the PAP stain, the cell is larger
than a neutrophil and has a characteristic bean shaped nucleus.
The macrophage is, after the fibroblast, the most
abundant cell in connective tissue. The activated macrophage is
difficult to describe because it has a very variable aspect. This
cell often presents itself with so many cytoplasmic inclusions
that the cell's structures are completely masked. Inclusions are
of several types, but the droplet is the most frequent. A classic
easy to identify macrophage, is the giant cell that contains one
or two smaller phagocyted cells in its cytoplasm. But this form
is exceptional; the majority of the macrophages are of average
size with a lot of inclusions.
The macrophages are frequent in acute inflammations. The
macrophage loaded with fat droplets is frequently found in many
body fluids. These are usually related to a chronic inflammation
process. In urine, when these droplets form a maltese cross when
viewed between crossed polarized filters, the macrophages are
then called oval fat bodies.