Urine

88 Cells

Introduction to Cells

Cellular elements appearing in the urine can originate from the bloodstream, the renal parenchyma, or the epithelium lining the lower urinary tract. In the male, cells originating within the reproductive organs can also be present in the urine, as the urethra is a com-mon conduit for both urine and cells originating in the male reproductive system. In addition, some cellular elements can be introduced into the urine from exter-nal sources, usually by contamination from the female genital tract, from fecal material, or in patients with pathologic fistulae. Cells in the urine can also represent neoplastic elements from solid tumors or lymphomas.

Cellular elements of the blood in small numbers are often a normal finding in the urine. Although refer-ences ranges vary, in general one to five erythrocytes and two to five leukocytes per high-power field are not considered abnormal in an asymptomatic patient. Erythrocytes can pass directly through the glomeru-lus, in which case they may appear dysmorphic, or through the epithelium, as part of trauma, infection, or a neoplastic process. They also can be an artifact of contamination by fecal or vaginal material. Erythro-cytes exposed to hypertonic urine for a period of time become crenated and can resemble foreign particles such as pollen.

Almost all leukocytes in the urine are neutrophils, introduced across an epithelial surface due to inflam-mation or neoplasm. Eosinophils are rare except in cases of interstitial nephritis. Lymphocytes also are rare and are usually associated with renal transplant rejection. Both can be extremely difficult to recognize unless special techniques are used to identify them.

“Case XVIII. This was a case of anasarca with coagulable urine having all its charac-ters well marked. There was no evidence either of hepatic disease or of derangement in the structure of the heart or lungs; but the urine loaded with red particles seemed to bespeak decided renal affection.”—Richard Bright (1789-1858). Reports of Medi-cal Cases, vol. 1, 1827. London: Longman.

Monocytes and macrophages are also rare except in cases of chronic hematuria from any cause.

Renal tubular epithelial cells are usually a sign of renal parenchymal disease, either inflammation or toxic tubular damage for any reason. In patients with lipiduria and nephrosis, renal tubular epithelial cells ac-cumulate fat droplets and are referred to as “oval fat bodies.”

Other epithelial cells are often not abnormal. Both squamous and transitional epithelial cells are frequent findings. Not all laboratories differentiate squamous and transitional epithelial cells, but there are good reasons to do so. Although squamous epithelial cells normally are present only within the urethra, they can originate from the prostate in patients with old infarcts and can involve more proximal portions of the urinary tract as a result of chronic inflammation or injury, or in rare cases of squamous cell neoplasms of the lower uri-nary tract. Squamous epithelial cells can also be pres-ent in the urine as a contaminant, often from vaginal fluids.

Although cells from the male reproductive system, particularly the prostate, can appear in the urine, they are difficult to recognize. The most common cell origi-nating from this source is the spermatozoon, and not all laboratories report their presence. However, there are some clinical circumstances in which they are an important finding. Neoplastic cells can be recognized in the urine but usually require special collection and staining techniques to do so. They are extremely dif-ficult to recognize by standard methods of urinalysis employing an unstained urine sediment.

Matula of Cells

Polydore Jean Charles Pauquet (after a 1493 manuscript). A physician in traditional garb examines urine flask of female patient in bed. 89

90 Cells

ErythrocyteErythrocytes in urine are similar to those seen in other sites. They generally retain their uniform size and bi-concave disk shape and usually contain hemoglobin. In older specimens or hypertonic specimens where analysis is delayed, the cells may become crenated and resemble foreign objects such as pollen grains. In hypotonic specimens, hemoglobin pigment is vari-ably lost and cells may be reduced to colorless spheri-cal membranes (“ghost cells”) and resemble fat, oil droplets, or yeast. In situations where identification is ambiguous, use of special imaging techniques such as polarization can be helpful. Nucleated red cells or sick-le cells can rarely be found in patients with sickle cell disease. Macrophages containing ingested red cells or hemosiderin may be observed in any patient with chronic hematuria.

SynonymS RBC, red cell

VItal StatIStICSsize �� diameter 7-8 μmshape �� round to slightly oval bi-

concave disk, crenated in hypertonic specimens with irregular edges and sur-faces, spherical “ghost” cells in hypotonic specimens

nuclear shape �� not applicablechromatin �� not applicablecytoplasm �� pale yellow-orange, may be

colorless; shades of red to purple in stained specimens

KEy dIffErEntIatIng fEaturESuniform size and general shapevariable amounts of hemoglobin pigment

present

PotEntIal looK-alIKESyeast cellspollen grainsstarch granulesperm headsfree fat dropletsair bubblessmall granulocytes (crenated specimens)calcium oxalate crystals (monohydrate form)

aSSoCIatEd dISEaSE StatES/CondItIonSnormal in small numbers (<5 per hpf)glomerular diseasestraumaneoplasmsurinary tract calculiurinary infectionsystemic coagulopathiesanticoagulants, some chemotherapeutic agents,

other medicationsPNH or other intrinsic red cell disorderscontaminated specimen (vaginal, etc�)

Erythrocytes(unstained)

round, refractile, biconcave disk

may be colorless, pale pink or pale yellow

refractive index varies by hemoglobin content; “ghost cells” seen with low hemoglobin

hour-glass appearance when cell is viewed on end

thin membrane

Cells 91

CM-14, 2006 (unstained, X160)Identification Referee % Participant %Erythrocyte 100.0 97.1

This urine specimen was obtained from a 77-year-old female who was a resident of a long-term care facility, with diagnoses of severe osteoporosis and dementia. She had recently become confused and her urine was cloudy and foul smelling. Urinalysis showed: pH=6.5; specific gravity=1.014; leukocyte esterase, blood, glu-cose and protein=positive; blood, protein, nitrite, glu-cose, ketones=negative.

Three red cells are clearly seen in this image and show typical orientations of on edge (clearly demon-strating the biconcave shape), en face, and slightly rotated with an eccentric pale zone. All are uniformly round, contain hemoglobin, and should not be con-fused with any of the potential look-alikes.

CM-13, 2000 (unstained, X160)Identification Referee % Participant %Erythrocyte 100.0 98.1

This urine specimen is from an 80-year-old male com-plaining of right flank pain. Urinalysis showed: pH=6.5; specific gravity=1.020; protein=2+; blood=2+.

Scattered throughout the field are numerous red cells containing almost no hemoglobin (ghost cells). Others have an irregular shape with a suggestion of spike-like projections and could represent early ex-amples of crenated red cells. The empty cells can be identified as red cells by their uniform size, lack of a thick refractile membrane, and absence of buds. Fi-nally, occasional cells scattered throughout the field exhibit internal cytoplasmic folds or creases that could be confused with starch except for their coloration. If identification of these cells was of particular concern, this could be resolved using special imaging tech-niques such as polarized light or interference contrast microscopy. Ultimately this patient was found to have a urinary calculus.

In hypertonic urine, the red cells shrink and wrinkle, becoming crenated.

92 Cells

CM-02, 1989 (unstained, X160)Identification Referee % Participant %

Erythrocyte 94.7 93.4Fat – free fat droplets 5.3 2.3Red blood cell cast - 2.0

This urine sample was obtained from a 34-year-old parturient patient who subsequently delivered a nor-mal male child. Her pregnancy was complicated by hypertension, and she developed renal failure in the immediate postpartum period.

Both arrowed objects are of yellow-red color indi-cating they contain hemoglobin, and therefore the diagnosis of free fat droplets is incorrect. Two of the unarrowed red cells are deformed and could, in the right clinical setting, raise some concern as to whether or not they are “dysmorphic.” Although these par-ticular cells do not meet the morphologic criteria for dysmorphic red cells, identification of cells such as this should result in a critical evaluation of both the urine and the patient to see if dysmorphic red cells might be present.


Erythrocyte 100.0 98.4

This urine was obtained from a 67-year-old male com-plaining of “smoky” urine and weight loss. Urinalysis showed: pH=5.0; specific gravity=1.012; protein=trace; blood=positive.

The arrowed objects are erythrocytes. None have any of the features of casts or crystals and should not be confused with them. All of the red cells in this field contain abundant hemoglobin. Isolated cells near the center and at the bottom of the field are smaller with small spike-like projections consistent with crenated forms. The large object near the center is a neutrophil, identifiable by the folded nucleus and granular cyto-plasm.

Unexplained hematuria in the absence of casts or crystals can be seen in patients with urinary tract neo-plasms.

Cells 93

This field contains a large mass of erythrocytes, as seen in the urinary sediment. Erythrocyte clumps in the urinary sediment can be an artifact of specimen preparation or can represent a blood clot. Individual cells are small and frequently have an orange tint due to the hemoglobin they contain. If trapped WBCs can be identified, the possibility of a blood clot should be considered. It is important to not mistake clumps of red cells for a red cell cast. In this example, there is no evidence of a protein matrix.

This image is a photomicrograph of the urinary sedi-ment using interference contrast microscopy. This technique imparts a three-dimensional appearance to the image and allows visualization of inclusions or oth-er internal structural details. These cells are of uniform size, and the prominent spicules represent infoldings of the membrane due to loss of intracellular water when the cells are present in hypertonic urine. Crenated red cells can be confused with pollen grains or white cells, especially lymphocytes, but the lack of internal struc-tural details establishes the origin in this case.

This interference contrast photomicrograph illustrates several normal red cells. Some cells clearly have a cen-tral indentation representing a biconcave disk. Two mucous strands adherent to an unidentified cell can be seen at the bottom of the photomicrograph.

Additional Examples of Red Blood Cells

94 Cells

This interference contrast photomicrograph illustrates several normal red cells. Some cells clearly have a cen-tral indentation representing a biconcave disk. Bud-ding yeast would have a capsule and, often, some internal structure. Fat droplets vary in size and, when viewed with polarized light, would be birefringent with “Maltese cross” formation.

Abnormal red cells could have some similarities. Dysmorphic red cells often form buds and could be similar to the overlapping normal cells seen to the left of center. However, dysmorphic red cells vary in size and, when viewed with ordinary bright-field illu-mination, would clearly not be normal cells. Another consideration would be the rare instance where red cells containing inclusions (Howell-Jolly bodies, para-sites such as malaria or babesia) were present in the urinary sediment. These cells would all demonstrate some internal structure when viewed with interference contrast microscopy and would likely vary in size. Ex-amination of a stained specimen could also resolve the issue if required.

This is a bright-field image of the urinary sediment. Numerous normal erythrocytes are present, many ap-pearing as biconcave disks with central pallor. Normal granulocytes with discrete nuclear lobation are pres-ent; the one at the lower left edge of the image ap-pears to have an overlying erythrocyte.

This is a bright-field image of the urinary sediment from a case of trauma. Several normal erythrocytes are present, easily recognized by their red-orange color and biconcave disk shape. A short red cell cast is pres-ent in the center of the image.

Additional Examples of Red Blood Cells

Cells 95

RBC Mimics

YeastBoth round and oval forms are found, but these can vary in size and can show “budding.”

Fat DropletsFree lipid droplets have a uniform round appear-ance but vary in size. Variability in size dis-tinguishes fat droplets from RBCs.

Air Bubbles Bubbles are round, variable in size, and demonstrate dark refractile periphery.

Sperm Heads of sperma-tozoa may become separated from the tails and mimic budding dysmorphic RBCs. They are gen-erally smaller than RBCs.

Neutrophils Necrobiotic granulo-cytes may be small with an irregular surface mimicking crenated RBCs. In concentrated urine, WBCs can also shrink and resemble RBCs; granules and nuclei are usually visible, however.

StarchStarch granules are small, slightly larger than a RBC, and often have a central indented or slit-like area.

Calcium OxalateMonohydrate form may contain oval and round refractile elements. Find-ing dihydrate forms in adjacent fields will help to distinguish the crystals from RBCs.

PollenGrains of pollen can be round or oval but are much larger than RBCs, typically 20 µm or more in diameter.

96 Cells

Erythrocyte, dysmorphic A morphologic variant of the red cell, the “dysmor-phic red cell” is considered quite specific for hematuria associated with glomerulonephritis. Dysmorphic red cells may be smaller than normal erythrocytes and ex-hibit cytoplasmic bulges or projections that may break off and appear as tiny separate red cell fragments. The classic example of this type of cell is one with two small symmetrically positioned cytoplasmic blebs (“Mickey Mouse ears”). This morphology is discussed further in the Closer Look section on dysmorphic red blood cells, page 100.

SynonymSRBC, red cell, acanthocyte, G1 cell

VItal StatIStICS size�� diameter 7-8 μm, but may

varyshape �� round to slightly oval, but

exhibit cytoplasmic blebsnuclear shape �� not applicablechromatin �� not applicablecytoplasm �� pale yellow-orange, may

be colorless shades of red to purple in stained speci-mens

KEy dIffErEntIatIng fEaturEScytoplasmic blebs (“Mickey Mouse ears”)doughnut shape with one or more blebs (G1 cell

of Dinda)loss of limiting membrane with phase contrast

microscopy

PotEntIal looK-alIKESyeast cellsoil dropletsfree fat dropletssmall granulocytes (crenated specimens)red cell casts (if cast matrix is not appreciated)

aSSoCIatEd dISEaSE StatES/CondItIonSglomerular diseases

Dysmorphic red cells are typically smaller than RBCs.

cytoplasmic bulges and projections

Dysmorphic red blood cells in the urine have proven to be diagnosti-cally important as an indicator of glomerular bleeding.

smaller red cell fragments may accompany dysmorphic cells

Dysmorphic Red Blood Cells(unstained)

cytoplasmic blebs

Cells 97


Erythrocyte, dysmorphic 15.4 4.8Yeast/fungi 53.8 84.0Fat globules 23.0 9.7Erythrocyte 7.7 0.7

This urine was obtained from a 23-year-old male with hemoptysis and renal failure who subsequently devel-oped anuria. Urinalysis showed: specific gravity=1.012; leukocyte esterase, protein, blood=positive.

The arrowed objects are dysmorphic erythrocytes. The abnormal red cell membrane, resulting in formation of cytoplasmic blebs, is particularly well demonstrated in the right-hand panel using the Nomarski technique and can be contrasted with membrane details of the normal red cells in the upper portion of the photo-micrograph. The symmetric blebs seen in the lower arrowed cell demonstrate “Mickey Mouse ears.” This patient was eventually diagnosed with Goodpasture syndrome, a type of glomerulonephritis with simulta-neous immune complex deposition involving both the alveolar and glomerular basement membrane. These cells should not be confused with budding yeast, since the cells in question contain hemoglobin and do not have a thick refractile capsule. Fat globules are highly refractile and would exhibit bright birefringence when illuminated with polarized light. Normal erythrocytes would be of uniform size and would not demonstrate cytoplasmic blebs.

This case has not been refereed or viewed by the par-ticipant group but is included as another example of dysmorphic erythrocytes.

This urinary sediment is from a 21-year-old female with hypertension and edema of approximately 2 months duration, and significant renal failure with a BUN = 33 mg/dL (8-18 mg/dL), creatinine = 2.4 mg/dL (0.35-0.93 mg/dL).

Arrows point to classic examples of dysmorphic erythrocytes. In each case, they exhibit cytoplasmic buds or blebs. There is no evidence of a capsule sug-gestive of yeast, and both cells are red in color. These cells were not identified initially but were noted on subsequent review, and the physician was notified. Fur-ther evaluation, including an elevated anti-DNA titer, established the diagnosis of lupus glomerulonephritis. It is important for laboratorians to be familiar with this unusual presentation of glomerular hematuria. Dys-morphic red cells are a significant abnormality and are a good candidate for “critical values” in urinalysis.

Additional Examples of Dysmorphic Red Blood Cells

98 Cells

This a photomicrograph of the urine in a patient with hematuria. Two dysmorphic red cells are present near the center of the image, with the upper cell having nu-merous cytoplasmic blebs, some of which are perpen-dicular to the imaging plane and are actually pointing directly at the viewer.

This is a bright-field image of a urinary sediment con-taining dysmorphic red cells. The cell at the top near the center shows a developing surface bleb; the one near the bottom shows a fully developed bleb with a narrow connecting stalk.


These are dysmorphic red blood cells in the urine as visualized using phase contrast microscopy. This tech-nique utilizes a special phase condenser to separate light rays passing through a specimen that are either unaffected (surround waves) or altered (particle waves) by various structures, such as membranes or internal particulate matter. These waves are of different am-plitudes, and the resolved image sharply contrasts relatively transparent areas of the object with various internal elements, rendering internal details visible. One of the advantages of phase contrast microscopy is that it can be used with unstained—even living—specimens. In this image, the cell in the upper right is a classic dysmorphic red cell with two small surface blebs representing “Mickey Mouse ears,” and the more cen-tral cell contains multiple surface blebs.

Cells 99

This bright-field image illustrates several dysmorphic red cells. The one on the right is a classic “Mickey Mouse ears” cell, while others manifest only single cy-toplasmic blebs.

This is a patient, unknown age, with a history of glo-merulonephritis. The central feature is a large red gran-ular cast with no clearly identifiable cells. This is a good example of a blood – hemoglobin pigment cast. The background contains large numbers of red cells, and several of these (arrows) are good examples of dys-morphic red cells, exhibiting prominent surface blebs.


RBC Shapes

Normalround biconcave disk, high refractive index, 6-8 µm in size

Ghost Celllow refractive index; hard to see due to low hemoglobin content

Crenatedhypertonic solution produces shrunken cell with uniform projections

Dysmorphicdistorted shape; classic exam-ple associated with glomerular bleeding has pronounced blebs, which may detach

isomorphic dysmorphic

100 Cells

Dysmorphic red cells, initially described in early 19th century German literature, were “rediscovered” in 1979 by Birch and Fairly [1], who considered them to be highly specific for glomerular hematuria (i.e., glomeru-lonephritis). Identification of a specific morphologic variant of the dysmorphic red cell (G1 cell) by Dinda [3] is now considered to be somewhat more specific for hematuria of glomerular origin. Identification of these cells is based on finding them in suspension in the urinary sediment. Unfortunately, a few subsequent publications describing various “poikilocytes” in air dried and stained urinary sediments as dysmorphic red cells has confused the classification.

True dysmorphic red cells may be smaller than normal and exhibit cytoplasmic bulges or projections that may break off and appear as tiny separate red cell fragments. The classic example of this type of cell is one with two small symmetrically positioned cytoplas-mic blebs (“Mickey Mouse ears”). These cells can be seen with conventional bright-field microscopy but are more easily seen with interference contrast (No-marski) imaging. Initial studies suggested that these morphologic changes represented disruption of the limiting membrane of the erythrocyte during transit into Bowman’s space across a damaged glomerular basement membrane [2]. Subsequent studies have shown that high concentrations of uric acid, as well as exposure to hypotonic osmotic solutions that mimic

dysmorphic red Cellsthose found in the tubules of the nephron, may also be important in inducing the morphologic changes rec-ognized as “dysmorphic.”

Dysmorphic red cells may be seen in the urine of patients with other intrinsic renal diseases, such as polycystic renal disease, pyelonephritis, and rhabdo-myolysis with renal failure. These situations not with-standing, recognition of dysmorphic red cells remains important as they are a sign of serious renal pathol-ogy. It is also important not to confuse these cells with yeasts, free fat, oval fat bodies, or starch, none of which are red in color (dysmorphic red cells can be easily dif-ferentiated in confusing cases by using polarized light microscopy).

The identification of dysmorphic red cells is based upon light microscopic techniques. Recently the iden-tification of dysmorphic red cells by conventional light microscopy was contrasted with their identification by flow cytometry in group of 206 urine samples from pa-tients with hematuria (127 with hematuria of glomeru-lar origin and 79 with nonglomerular hematuria). The two methods had comparable sensitivities of 99%, but the specificity was 42% for flow cytometry and 98% for conventional microscopy [4].

Based on their findings the authors concluded that microscopic analysis remains the preferred method of evaluating patients with hematuria.

Cells 101

With minor damage to the basement membrane, only large protein molecules are lost into the urine.

Increasing damage to the basement mem-brane and podocytes allows RBCs to move into Bowman’s space.

RBC membranes are disrupt-ed if the basement membrane damage is severe.

As the damaged RBCs traverse the length of the nephron, osmotic and physical forces produce the dysmorphic appearance.

Blood in the urine may originate from the glomerulus or the collecting duct system and bladder. If the RBCs are dysmorphic, the bleeding is most likely of glomerular origin, in which case immune or nonimmune glomerulonephritis should be ruled out. This may require a kidney biopsy.

High concentrations of uric acid and exposure to hypotonic os-motic solutions can also induce dysmorphic RBC morphology.

Glomerular HematuriaBowman’s space

capillaries

endothelial cell

hematuria

podocyte

podocyte

basement membrane

protein molecules

damaged glomerular basement membrane; foot processes are lost (fused)

fused foot processes

Glomerulus

Glomerular Capillary

arterioles

Urine

Documents

squamous epithelial

neoplastic cells

hypertonic urine

transitional epithelial

yeast cells

renal tubular epithelial

coagulable urine

spherical ghost cells