Microscopic Examination of Urine

Comprehensive practice flashcards covering cellular morphology, casts, crystals, and artifacts evaluated during microscopic examination of urine sediment.

When is a macroscopic screening of urine sediment indicated?

When requested by a physician, when testing specific patient populations (pregnant women, pediatric, diabetic, renal patients), or when any abnormal physical or chemical result is obtained (color, clarity, blood, protein, nitrite, leukocyte, or glucose).

What is the standard procedure for microscopic examination of urine sediment?

Examine under reduced light due to refractive index; scan $10$ fields on low power ($10\times$) including the coverslip perimeter for casts, then examine $10$ fields on high power ($40\times$), focusing on an epithelial cell to establish the correct plane.

How are urinary casts, RBCs, and WBCs quantitatively reported?

Casts are reported as the average number per low-power field ($\text{lpf}$), while RBCs and WBCs are reported as the average number seen in $10$ high-power fields ($\text{hpfs}$).

What are the normal reference value and diameter of red blood cells in urine sediment?

The normal reference value is $0\text{--}3$ per high-power field ($\text{hpf}$), and their diameter is approximately $\text{7 mm}$ (must be identified using high power).

How do RBCs appear in hypersthenuric versus hyposthenuric urine?

In hypersthenuric urine, RBCs become crenated due to water loss; in hyposthenuric urine, RBCs swell and lyse, leaving faint ghost cells.

What is the clinical significance of dysmorphic RBCs (acanthocytes) in urine?

They are associated with glomerular bleeding and strenuous exercise.

What are glitter cells and what causes them to form?

They are neutrophils swollen in hypotonic urine where Brownian movement of their granules creates a sparkling appearance; they stain light blue with Sedi-Stain and have no pathological significance.

What stain is used to identify urinary eosinophils and what do they indicate?

Hansel stain is used (reported as a percentage of $100$ cells); their presence indicates drug-induced interstitial nephritis, urinary tract infections, or transplant rejection.

What are clue cells and what do they indicate in urine sediment?

Squamous epithelial cells covered in bacteria (Gardnerella) that extend past the cell borders giving a raggedy appearance; indicative of bacterial vaginosis.

Where do transitional epithelial cells originate, and what are syncytia?

They originate from the lining of the renal pelvis, calyces, ureters, bladder, and upper male urethra; syncytia are clumps or sheets of these cells commonly seen after invasive urologic procedures.

How do renal tubular epithelial (RTE) cells from the proximal tubule, distal tubule, and collecting duct differ morphologically?

Proximal tubule cells are large, rectangular, and columnar with granular cytoplasm; distal tubule cells are smaller, round or oval with an eccentric round nucleus; collecting duct cells are cuboidal (never round).

What are renal fragments and what is their clinical significance?

Renal fragments are groups of $3$ or more RTE cells originating from the collecting duct (often seen in large sheets); their presence indicates severe tubular injury or necrosis.

Identify this lipid-containing renal tubular epithelial structure found in urine sediment.

Oval fat body.

What microscopy and staining techniques confirm the presence of lipids in oval fat bodies?

Staining with Oil Red O or Sudan Black stains neutral fats and triglycerides orange-red; polarizing microscopy confirms cholesterol by showing a 'Maltese cross' birefringent pattern.

What are bubble cells?

Injured renal tubular epithelial cells containing large vacuoles whose cytoplasm dilates prior to cell death, seen in acute tubular necrosis alongside normal RTE cells and oval fat bodies.

Identify this flagellated parasite commonly encountered in urine sediment.

Trichomonas vaginalis.

Identify this formed element in urine sediment that is reported simply as 'present'.

Spermatozoa.

Identify this low-refractive-index threadlike element present in urine sediment.

Mucus threads.

What is the major constituent of urinary casts and mucus?

Uromodulin, also known as Tamm-Horsfall glycoprotein (THP), which is excreted by RTE cells of the distal convoluted tubule and upper collecting duct.

What conditions favor the gelling and formation of urinary casts?

Urine-flow stasis, acidity, and an increased concentration of sodium and calcium.

Identify this urinary cast consisting of nearly pure uromodulin.

Hyaline cast.

What is the normal reference range for hyaline casts in urine sediment?

$0\text{--}2$ per low-power field ($\text{lpf}$).

Identify this urinary cast containing intact or deteriorating erythrocytes.

RBC cast.

What clinical condition is associated with granular 'dirty brown' casts?

Massive hemoglobinuria or myoglobinuria associated with acute tubular necrosis.

How can a WBC cast be differentiated from a WBC clump?

By verifying the presence of a distinct protein cast matrix enclosing the white blood cells, alongside free WBCs in the sediment.

Identify this urinary cast containing bacilli bound within a protein matrix.

Bacterial cast.

Identify this urinary cast characteristic of disorders producing lipiduria such as nephrotic syndrome.

Fatty cast.

What disease entities are indicated by mixed casts containing RBCs + WBCs versus WBCs + RTEs/bacteria?

RBC and WBC casts indicate glomerulonephritis, whereas WBC and RTE cells or WBC and bacterial casts indicate pyelonephritis.

Identify this urinary cast that may form from strenuous exercise or cellular disintegration.

Granular cast.

Identify this urinary cast with a high refractive index, jagged ends, and notched edges indicative of chronic renal failure.

Waxy cast.

Identify this wide cast type known as a 'renal failure cast' that molds to dilated distal convoluted tubules.

Broad cast.

What is the general pH rule for the occurrence of abnormal urine crystals?

All abnormal urine crystals are found in acidic urine (rarely in neutral pH).

Which normal acidic crystals are yellow to reddish-brown in color?

Urate crystals (amorphous urates, uric acid, acid urates, and sodium urates).

Identify this classic pyramid or 'envelope' shaped normal acidic urine crystal.

Calcium oxalate dihydrate crystal.

What is the clinical significance of oval or dumbbell-shaped calcium oxalate monohydrate crystals?

They are characteristic of ethylene glycol poisoning.

How do refrigerated precipitates of amorphous urates differ from amorphous phosphates?

Amorphous urates precipitate as a pink sediment in acidic urine; amorphous phosphates precipitate as a white sediment in alkaline urine that does not dissolve upon warming.

Identify this prism-shaped normal alkaline urine crystal commonly known as a 'coffin lid'.

Triple phosphate crystal.

Identify this yellow-brown 'thorny apple' shaped normal alkaline urine crystal.

Ammonium biurate crystal.

Identify these colorless hexagonal plates found in acidic urine.

Cystine crystals (indicative of cystinuria; confirmed using the cyanide-nitroprusside test).

Identify this abnormal crystal displaying rectangular plates with notched corners.

Cholesterol crystal.

Identify this abnormal crystal presenting as fine needles arranged in rosettes or clumps.

Tyrosine crystals (associated with severe liver disease or amino acid metabolism disorders).

Identify this abnormal crystal characterized by concentric rings and radial striations.

Leucine crystal.

Identify this abnormal golden-brown crystal that appears as clumped needles or granules in hepatic disorders.

Bilirubin crystal.

Identify this medication crystal that can form 'sheaves of wheat' or rosettes in acidic urine.

Sulfonamide (sulfa) crystal.

How can radiographic contrast media crystals be distinguished from cholesterol crystals?

Both appear as notched flat plates, but radiographic dye crystals are accompanied by a markedly elevated specific gravity ($\text{SG}$).