CH.7 Microscopic Examination of Urine

When is microscopic urine examination performed?

Based on physical and chemical findings, clinician request, specified patient populations, abnormal results, or reflex criteria.

What are the main formed elements identified in urine?

RBCs, WBCs, epithelial cells, bacteria, yeast, parasites, sperm, mucus, casts, crystals, and artifacts.

How should urine sediment be examined under the microscope?

Low power (10×): locate casts and assess general composition. High power (40×): identify and count most other elements.

How are formed elements reported microscopically?

Casts: average per low-power field (LPF). RBCs/WBCs: average per high-power field (HPF). Other elements use field counts or semiquantitative terms.

Why must urine be examined fresh or preserved?

RBCs, WBCs, and casts lyse quickly in dilute, alkaline urine. Refrigeration can precipitate urates, phosphates, and crystals.

What is Sternheimer–Malbin stain used for?

Crystal violet and Safranin O increase visibility of WBCs, epithelial cells, and casts by increasing their refractive index.

Which stains help identify specific urine components?

Oil Red O/Sudan III: lipids. Gram stain: bacterial casts. Hansel stain: eosinophils. Prussian blue: hemosiderin granules.

What are normal RBCs like, and how can urine alter their appearance?

Small, smooth, non-nucleated biconcave discs. Concentrated urine causes crenation; dilute urine may lyse them into ghost cells.

What are dysmorphic RBCs, and what can acanthocytes indicate?

RBCs with abnormal shapes, including fragmented or hypochromic forms. Acanthocytes are associated with glomerular disorders.

Why might the blood dipstick be positive when no RBCs are seen?

RBCs may have lysed, releasing hemoglobin. The test may also detect myoglobin or other interfering peroxidase activity.

Why might RBCs be seen when the blood dipstick is negative?

Ascorbic acid can cause a false-negative blood reaction, or the apparent RBCs may be look-alikes such as yeast or crystals.

What is the reference value and significance of urinary RBCs?

Approximately 0–3 or 5 RBCs/HPF, depending on the reference used. Increased RBCs indicate hematuria and may reflect renal or urinary tract injury.

How do RBC casts help localize bleeding?

RBC casts indicate bleeding within the nephron, commonly associated with glomerular damage. RBCs without casts may reflect bleeding lower in the urinary tract or contamination.

What are urinary WBCs, and what are glitter cells?

Neutrophils are the predominant WBCs and have lobed nuclei and granules. Glitter cells are swollen neutrophils in hypotonic urine whose granules show Brownian movement.

How are urinary eosinophils detected and interpreted?

Concentrate sediment, stain with Hansel stain, and assess the percentage among 100–500 cells. More than 1% is significant; eosinophils are associated with drug-induced nephritis and transplant rejection.

What is the normal WBC reference value, and what is pyuria?

Normally fewer than 5 WBCs/HPF. Pyuria means increased urinary WBCs and may occur with bacterial infections or nonbacterial inflammation.

What conditions can cause increased urinary WBCs?

Cystitis, pyelonephritis, prostatitis, urethritis, glomerulonephritis, lupus, interstitial nephritis, and tumors.

How do squamous epithelial cells appear, and where do they originate?

They are the largest urinary epithelial cells and originate from the vagina and lower urethra. Small amounts can reflect normal shedding or specimen contamination.

What are clue cells, and what are they associated with?

Squamous epithelial cells covered with coccobacilli extending over their edges. They are associated with Gardnerella vaginalis and bacterial vaginosis.

Where are transitional epithelial cells found, and what is their significance?

They line the renal calyces, renal pelvis, ureters, bladder, and part of the male urethra. Increased cells may occur with inflammation, infection, urinary procedures, or carcinoma.

How do spherical, caudate, and polyhedral transitional cells differ?

Spherical cells: superficial layer. Caudate cells: intermediate layer. Polyhedral cells: deep basal layer. Sheets may follow instrumentation; clumps may raise concern for malignancy.

What are renal tubular epithelial (RTE) cells, and why are they important?

Cells lining kidney tubules. Increased RTE cells suggest tubular injury or disease; they are among the most clinically significant urinary epithelial cells.

How can PCT, DCT, and collecting duct epithelial cells be distinguished?

PCT: relatively large, columnar/rectangular, convoluted. DCT: smaller, round/oval, eccentric nucleus. Collecting duct: cuboidal with at least one straight edge and an eccentric nucleus.

What is a renal fragment?

A group of at least three intact cuboidal RTE cells, often in sheets. It suggests basement membrane destruction and significant renal tubular injury.

What are oval fat bodies, and what do they indicate?

RTE cells containing absorbed fat. Lipid stains confirm fat; cholesterol produces a Maltese cross under polarized light. Associated with nephrotic syndrome, tubular necrosis, diabetes, and crush syndromes.

What are the key findings for urinary bacteria and UTI?

Rods are most common; cocci can also occur. Nitrite helps detect certain nitrate-reducing bacteria, especially many rods. WBCs usually accompany bacteria in a UTI.

How can urinary yeast be identified, and when is it clinically relevant?

Refractile budding cells or hyphae. Associated with diabetes/glucosuria, immunocompromise, and vaginal Candida. Nitrite is often negative even when WBCs are present.

What is the most common urinary parasite, and how does it appear?

Trichomonas vaginalis: a pear-shaped flagellate that moves rapidly across the microscopic field.

How do spermatozoa appear in urine, and what is their significance?

Oval tapered heads with long tails; they are usually immobile because urine is toxic to sperm. They are rarely significant but may affect protein results.

What is urinary mucus made of, and how does it look?

Protein material, including Tamm–Horsfall protein (uromodulin), produced by renal tubular, glandular, and epithelial sources. It appears threadlike with low refractivity and irregular shape.

Where do casts form, and what do they reveal?

Casts form mainly in distal convoluted tubules and collecting ducts. Their composition reflects conditions within the nephron.

How do urinary casts form?

Tamm–Horsfall protein gels during urinary stasis, especially in acidic urine with sodium and calcium. It aggregates, traps cells or other elements, forms a matrix, detaches from the tubule, and is excreted.

What are hyaline casts, and what is their clinical significance?

Colorless, low-refractive casts made mainly of protein. About 0–2/LPF may be normal. They can occur with exercise, stress, fever, heat, dehydration, or renal and cardiac disease.

What do RBC casts indicate, and what are their typical findings?

Bleeding within the nephron, often from glomerular or capillary damage. Associated with acute glomerulonephritis and nephritic syndrome. They may appear orange-red; prolonged stasis can degrade their hemoglobin.

What is the significance of WBC casts?

They indicate inflammation or infection involving renal tubules. WBC casts with bacteria suggest pyelonephritis; WBC casts without bacteria may suggest acute interstitial nephritis.

What are fatty casts associated with?

Oval fat bodies and free fat droplets. They are highly refractile and can be confirmed with lipid stains or polarized microscopy. Associated with nephrotic syndrome, diabetes, crush trauma, and tubular necrosis.

How do granular casts form, and why are they important?

They contain coarse or fine granules and may be pathological or nonpathological. Degeneration can produce waxy casts. Look for a cast matrix to distinguish them from debris or crystals.

What are waxy casts, and what do they indicate?

Highly refractile, brittle, often fragmented casts with jagged ends or notches. They are degenerated hyaline/granular casts and indicate extreme urinary stasis, often in chronic renal failure.

What are broad casts, and why do they occur?

Wide casts associated with chronic renal failure and widening/destruction of tubules. Any cast type can be broad, but granular and waxy forms are common.

How can artifacts be distinguished from casts?

Artifacts include fibers, hair, powder, pollen, oil droplets, and contaminants. Look for the cast matrix; most casts do not polarize, unlike some fibers and fatty casts.

Why are crystals in fresh urine more clinically useful?

They may form in vivo and can indicate or contribute to tubular damage. Identification relies on shape, color, urine pH, and sometimes polarized microscopy.

What factors influence urine crystal formation?

Solute concentration, temperature, urine pH, and specimen age. Crystals in fresh urine are associated with high specific gravity.

How do amorphous urates differ from amorphous phosphates?

Amorphous urates: refrigerated acidic urine, yellow-brown sediment, dissolve with heat. Amorphous phosphates: refrigerated alkaline urine, heavy white precipitate, dissolve in acetic acid.

How do uric acid crystals appear, and what are they associated with?

Rhombic, whetstone, wedge, or rosette shapes; yellow-brown or colorless. They polarize and are associated with gout or chemotherapy for leukemia.

How do calcium oxalate crystals appear, and why are they important?

Colorless envelope/two-pyramid shapes are common; monohydrate forms may be oval or dumbbell-shaped. They occur in acid or neutral urine and are a major component of kidney stones. Monohydrate forms can occur with antifreeze poisoning.

How do triple phosphate crystals appear?

Colorless, prism-shaped or coffin-lid crystals that polarize. They may occur in highly alkaline urine and UTIs and are generally not clinically significant by themselves.

How do ammonium biurate crystals appear, and when are they seen?

Yellow-brown spheres with spicules, resembling thorny apples. They occur in alkaline urine, especially old specimens and with urea-splitting bacteria.

What do cystine crystals look like, and what causes them?

Thin or thick hexagonal plates in acidic urine. They indicate cystinuria, an inherited defect in cystine reabsorption, and can cause renal calculi.

What do cholesterol crystals look like, and what are they associated with?

Rectangular plates with notched corners, often seen in refrigerated specimens. Polarized light helps identify them; they are associated with lipiduria and nephrotic syndrome.

How do bilirubin crystals appear, and what do they indicate?

Yellow clumped needles or granules. Associated with liver disease, such as viral hepatitis with tubular damage, and a positive urine bilirubin strip.

How do tyrosine and leucine crystals differ?

Tyrosine: fine yellow needles in clumps or rosettes. Leucine: yellow-brown spheres with concentric rings and radial striations. Both may occur with inherited amino acid disorders and give a positive bilirubin strip in the slides.

What are the key medication-related urinary crystals?

Ampicillin: colorless needles/bundles after refrigeration, associated with high doses and inadequate hydration. Sulfa crystals: varied shapes, often in patients treated for UTIs. Radiographic dye may also crystallize.