I. Microscopic ExaminationIn 1926, the standardized quantitative microscopic examination of urine sediment made its clinical laboratory debut. Microscopic examination of urine sediment continues to play an important role in the initial diagnosis and monitoring of renal disease.

A. Cellular Elements or Formed Elements in Urine Sediment A wide range of formed elements can be encountered in the microscopic examination of urine sediment. These formed components can originate from throughout the urinary tractfrom the glomerulus to the urethraor can result from contamination (e.g. menstrual blood, spermatozoa, fibers, starch granules).A. Red Blood Cells (Erythrocytes). The name erythrocyte comes from the Greek word erythros which means red and the suffix -cyte, meaning cell.Microscopic Appearance. The RBCs in urine are viewed and enumerated using high-power magnification because of their small sizeapproximately 8 m in diameter and 3 m in depth. RBCs have no nucleus; they normally appear as smooth biconcave disks, and they are moderately refractile.Red Blood Cells: Microscopic Features and Correlations

Microscopic Features Typical formsmooth, biconcave disks, 6-8 m in diameter; no nucleus

Look-alike elements Monohydrate calcium oxalate crystals Yeast cells

Correlation with physical and chemical examinations Urine colornote that a normal appearing urine can still have increased RBCs present Blood reactioncan be negative owing to ascorbic acid interference; degree of interference varies with reagent strip band

A. White Blood Cells (Leukocytes). Leukocyte is a collective term that refers to any type of white blood cell. In health, the distribution of WBCs in the urine essentially mirrors that of peripheral blood. The five types of cells that can be present are neutrophils, lymphocytes, basophils, eosinophils and monocytes (macrophages). Neutrophils ate the WBC most often observed in urine because they predominate in the peripheral blood. NeutrophilsMicroscopic Appearance. They measure approximately 14 m in diameter but can range from 10 to 20 m, depending on the tonicity of the urine. Neutrophils are larger than erythrocytes. They are spherical cells with characteristic cytoplasmic granules and lobed or segmented nuclei. Unstained, neutrophils have a graying hue and appeared grainy. EosinophilsIn routine microscopic examination of unstained urine sediment, the discrimination of eosinophils from neutrophils is often impossible despite their bilobed nuclei and slightly larger size. When specifically requested, urine specimens for eosinophil detection should be cytocentrifuged and stained using Hansel stain, which is a stain that is considered superior to Wright;s stain in detecting neutrophils in urine. LymphocytesThese leukocytes, even though normally present in urine, are usually not recognized because of their small numbers. However, lymphocytes are more readily apparent and identifiable when supravital stains are used or cytodiagnostic urinalysis using Wrights or Papanicolaous stain is performed. Monocytes and Macrophages (Histiocytes)These are actively phagocytic cells that are capable of phagocytizing bacteria, viruses, antigen-antibody complexes, RBCs and organic and inorganic substances like fat and hemosiderin. The primary functions of these cells are:1. To defend against microorganisms;2. To remove dead or dying cells and cellular debris; and,3. To interact immunologically with lymphoid cells.Microscopic Appearance. Monocytes range in diameter from 20-40 m. They have a single and large nucleus that is round to oval and often indented. The cytoplasm can be abundant and contains azurophilic granules. Because monocytes are actively phagocytic cells, large vacuoles often containing debris or organisms within them can be observed.Macrophages are derived from monocytes; when they reside in interstitial tissues, they are often called histiocytes. They can be as small as 10 m or as large as 100 m in diameter even though their average diameter varies from 30-40 m. Because macrophages are transformed form monocytes, they usually have irregular, kidney-shaped nuclei and abundant cytoplasm (vacuolated).Monocytes and macrophages are identified more easily by using supravital stains on the urine sediment or by making a cytocentrifuged preparation followed by Wrights or Papanicolaous stain.

White Blood Cells (WBCs): Microscopic Features and Correlations

Microscopic FeaturesNeutrophils Spherical cells, 12-14 m in diameter Granular cytoplasm Lobed nuclei Glitter cellsdilute urine (low SG)Lymphoctyes Spherical cells, 6-9 m in diameter MononuclearMonocyte and macrophages Spherical cells, 20-25 m in diameter Granular cytoplasm Mononuclear Cytoplasm often vacuolated with ingested debris

Look-alike elements Renal tubular epithelial cells (collecting duct cells) Dead trichomonads Crenated RBCs

Correlation with physical and chemical examinations Leukocyte esterase reactioncan be negative despite increased WBCs owing to excess hydration or when the WBCs are lymphocytes Negative nitrite reaction: suggestive of inflammation or nonbacterial infection Positive nitrite reaction: suggests bacterial infection

A. Epithelial Cells There are various types of epithelial cells seen in urine sediment. Basically, there are three types: squamous, transitional (urothelial), and renal tubular epithelial cells. The presence of large numbers of some cell types can indicate an improperly collected specimen, whereas increased numbers of others indicate a severe pathologic process. Whenever there are epithelial cells with abnormal characteristics such as unusual size, shape, inclusions, or nuclear chromatin pattern, additional cytologic studies are necessary. These cells may indicate neoplasia in the genitourinary tract or can result from treatments, such as chemotherapy or radiation.

Epithelial Cells: Microscopic Features and Clinical Significance

Cell TypeSiteRelative Size and DiameterMorphologyClinical Significance

SquamousFemales: line entire urethraMales: distal portion of urethra only40-60 m Shape: thin, flagstone-shaped with distinct cell borders Abundant cytoplasm; cytoplasmic granulation increases as cell ages Nucleus ~8-14 m,* centrally located; can be anucleated or multinucleated Increased numbers due to poor collection technique (ex: not a clean catch)

TransitionalBladderUretersRenal pelvesMales: majority of urethra20-40 m Shape varies with site:Superficial cells-round or pear-shapedIntermediate layer-smaller and roundBasal layer-small, elongated (or columnar-like) Moderate amount of cytoplasm Distinct cell borders that appear firm Nucleus ~8-14 m,* round or oval, centrally located Increased numbers with infection or inflammation of bladder, ureters, renal pelves or male urethra Cell clusters or sheets can occur after catheterization or instrumentation of urinary tract (ex: cytoscopy)

RenalCollecting duct cells

Small ducts: 12-20 m

Large ducts: 5-10 m

Small duct cells Shape: polygonal or cuboidal (Look for a flat edge) Nucleus: large, covers 60-70% of cell

Large duct cells Shape: columnar Nucleus: ~6-8 m, eccentric Increased numbers with ischemic events: Shock Anoxia Sepsis

Trauma

Convoluted tubular cells

Distal tubular cells: 14-25 m

Proximal tubular cells: 20-60 mDistal tubular cells Shape: oval to round Cytoplasm: grainy Nucleus: small, round, central or eccentric

Proximal tubular cells Shape: large, oblong or cigar-shaped with indistinct cell membrane (Note: Resemble granular casts with single inclusion) Cytoplasm: grainy Nucleus: usually eccentric; can be multinucleated Increased numbers with toxic events:Heavy metalsHemoglobinuria, myoglobinuria Poisons

Drugs

A. Casts Formation. Unique to the kidney, urinary casts are formed in the distal and collecting tubules with a core matrix of uromodulin (formerly known as Tamm-Horsfall protein). This glycoprotein is secreted by the renal tubular cells of thick ascending limb of loop of Henle (i.e., the straight portion of the distal tubules) and by the distal convoluted tubules. Any urinary component, whether chemical or a formed element, can be found incorporated into a cast.General Characteristics. Because casts are formed within the tubules, they are cylindrical and microscopically always appear thicker in the middle than along their edges. They have essentially parallel sides with ends that can be rounded or straight (abrupt). Hyaline castsThese are composed mainly of a homogeneous uromodulin protein matrix. They are the most commonly observed casts in the urine sediment. Appearance. These casts appear colorless in unstained urine sediment, with rounded ends and in various shapes and sizes. Stain. Hyaline casts become pink with Sternheimer-Malbin stain, and their edges are more clearly defined.Clinical Manifestations. Two or fewer hyaline casts per low-power objective is considered normal in healthy individuals. Increased numbers of hyaline casts can be found following extreme physiologic conditions such as strenuous exercise, dehydration, fever, or emotional stress. They also accompany pathologic casts in renal disease and in cases of congestive heart failure.A. Oval Fat Bodies Oval fat bodies are degenerating tubular epithelial cells filled that contain refractile fat droplets. These fats have been absorbed by the tubular cells after being leaked through abnormal glomeruli. They appear as grape-like clusters of variable size and are highly refractile.

B. UnorganizedCrystals. These result from the precipitation of urine solutes out of solution. They are not normally present in freshly voided urine but form as urine cools to room or refrigerator temperature (depending on storage). When crystals are present in freshly voided urine, they indicate formation in vivo and are always clinically significant.Contributing Factors. Several factors influence crystal formation, including:B. Concentration of solute in the urine;B. The urine pH; and,B. The flow of urine through the tubulesNormal Crystals Found in Normal Urine Specimen1. Uric acid. Uric acid crystals occur in many forms; the most common form is the rhombic or diamond shape. They may appear colorless when they are thin or when the urine is low in uroerythrin (a urine pigment). Uric acid crystals can be present only if the urine pH is less than 5.7.2. Amorphous urates. When the urine pH is acid (between pH 5.7 and 7.0), uric acid exists in its ionized form as a urate salt.3. Calcium oxalate. The most common shape of calcium oxalate crystals is their octahedral or pyramid form. They are colorless and may vary significantly in size. They are the most frequently observed crystals in human urine because they can form in urine at any pH.4. Amorphous phosphates. This noncrystalline form of phosphates resembles fine, colorless grains of sand in sediment. Like amorphous urates, amorphous phosphates have also no clinical significance.5. Calcium phosphate. They are classified as alkaline crystals because they are usually present in neutral or slightly basic urine specimens; however, they can also form in slightly acidic urine.6. Triple phosphate. Triple phosphates (NH4MgPO4, ammonium magnesium phosphate) crystals are colorless and appear in several different forms. The most common and characteristic forms are three- to six-sided prisms with oblique terminal surfaces, the latter described as coffin lids.7. Ammonium biurate. These crystals appear as yellow-brown spheres with striations on the surface. Irregular projections or spicules can also be present, giving these crystals a thorny apple appearance. They can form in alkaline or neutral urine.8. Calcium carbonate. Calcium carbonate crystals appear as tiny, colorless granular crystals. These crystals are not frequently found in the urine sediment and have no clinical significance.CrystalUrine pH

AcidNeutralAlkaline

Uric acid+

Amorphous urates+

Calcium oxalate++

Amorphous phosphates++

Calcium phosphate++

Triple phosphate++

Ammonium biurate+

Calcium carbonate+

Abnormal in Urine Sediment1. Cholesterol. These crystals appear as clear, flat, rectangular plates with notched corners. They can be present in acidic urine and, because of their organic composition, are soluble in chloroform and ether. They are rarely observed in urine sediment but can be seen with the nephrotic syndrome and in conditions resulting in chyluria: the rupture of lymphatic vessels into the renal tubules as a result of tumors, filariasis and so on.2. Cystine. These crystals appear as colorless, hexagonal plates with sides that are not always even. These clear, refractile crystals are often laminated or layered and tend to clump. Present primarily in acidic urine, cystine crystals are clinically significant and indicate disease, that is, congenital cystinosis or cystinuria.3. Tyrosine and Leucine. Tyrosine crystals appear as fine and delicate needles that are colorless or yellow, while leucine crystals are highly refractile, yellow to brown spheres. They have concentric circles or radial striations on their surface and can resemble fat globules. These amino acids are abnormal and are present in the urine of patients with overflow aminoaciduriasrare inherited metabolic disorder.Abnormal Crystals in Urine Sediment

CrystalMicroscopic Appearance

CholesterolColorless flat plates with notched or broken corners

CystineColorless, hexagonal plates

Hippuric acidColorless to yellow needles or prism-like structures

LeucineYellow-brown spherical crystals showing concentric circles

SulfaYellow to brown-green rosettes or bundles of needles

TyrosineColorless to pale yellow sheaves of needles

Source (Oval Fat Bodies):Oval Fat Bodies. (n.d.). Retrieved on April 15, 2015, from MediaLab Inc. website: https://www.medialabinc.net/spg30248/oval_fat_bodies.aspx