Microscopic Examination of Urine Part I

RBCs in Urine Microscopy

• Size: ~7 μm; no nucleus

• Normal range: 0–2 RBCs/hpf

• In concentrated urine, RBCs appear small and crenated

• Rarely seen unless there's contamination or pathology

Ghost Cells in Urine

• Seen in dilute (hypotonic) urine

• RBCs swell and lyse, but membranes remain intact

• Appear as empty, faint outlines

• Do not count in RBC estimate — just note as “present”

Contextual note:
Ghost cells result from osmotic lysis and may indicate prolonged urine dwell time in hypotonic conditions. Their presence helps explain low RBC counts when hematuria is suspected.

Red Blood Cells Confused with…

• Yeast: Budding; resists acetic acid lysis

• Oil droplets: Highly refractile, variable in size

• Air bubbles: Refractile and shiny; vary in size

• Fat globules: Persist with acetic acid; ID via Sudan III or polarized light

Confirmatory tip:
Add 1 drop of acetic acid to 1 drop of sediment — if RBCs disappear, blood was present. Yeast and fat will remain.

Hematuria Interpretation Pitfalls

• Hematuria = RBCs in urine

• Results may not match urine color or dipstick:

  • 1–4 RBCs/hpf, strip may be negative (threshold ≈ 5+ RBCs/hpf)

  • Positive dipstick, no visible RBCs → likely lysed RBCs, Hgb, or Mgb

Contextual note:
Dipstick detects peroxidase activity, so free hemoglobin or myoglobin can trigger a positive even in the absence of intact RBCs on microscopy.

Crenated RBCs vs WBCs

• Crenated RBCs: Shrink in hypertonic urine, appear granular

• May be mistaken for WBCs, but are smaller in size

• Acetic acid will lyse RBCs but not:

  • Yeast

  • Oil droplets

  • WBCs

Dysmorphic RBC

• Have cellular protrusions, variable size, may be fragmented

• Suggest glomerular bleeding

• Very rare finding; can occur post-strenuous exercise

• Requires confirmation by a second MLS or technical specialist

WBCs in Urine Microscopy

• Size: ~12 μm

• Normal range: 0–5 WBCs/hpf

• Usually neutrophils (PMNs):

  • Have granules and multi-lobed nuclei

  • Nucleus may be hard to see due to granules

WBCs in Varying Urine Osmolarity

• Hypertonic urine:

  • WBCs shrink, may not degranulate

  • May yield false-negative leukocyte esterase strip test

• Hypotonic urine:

  • WBCs swell → form glitter cells

  • Glitter cells show Brownian movement

  • Not clinically significant — just water-swollen WBCs

Pyuria

• Defined as ↑ WBCs in urine

• Indicates infection or inflammation in the genitourinary (GU) tract

• Possible causes:

  • Bacterial infection

  • Glomerulonephritis

  • Lupus erythematosus

  • Interstitial nephritis

  • Tumors

Mononuclear Cells in Urine

• Rare in routine urinalysis

• Lymphocytes:

  • Small, may mimic RBCs

  • Seen in early renal transplant rejection

• Monocytes, macrophages, histiocytes:

  • May appear vacuolated or contain inclusions

If large number of Mono nuclear refer to cytology

Eosinophils in Urine

• Not normally present in urine

• Significant if >1% of total WBCs

• Visualized with Hansel’s or Wright’s stain

Associated with:

• Drug-induced interstitial nephritis (most common)

• UTIs

• Parasitic infection (Schistosoma)

• Renal transplant rejection

Epithelial Cells in Urine

• Line the genitourinary tract

• Three main types:

  • Squamous

  • Transitional

  • Renal tubular

Squamous Epithelial Cells

• Largest cells in urinary sediment

• Prominent nucleus ≈ size of an RBC

• Easily seen at 10X; may appear folded/clumped

• Originate from vagina, female urethra, lower male urethra

• No pathological significance — normal sloughing

Clue Cells

• Squamous epithelial cells coated with Gardnerella vaginalis

• Appear granular and irregular

• Indicative of bacterial vaginosis (when numerous)

• Not typically reported on urine microscopy — seen on vaginal wet preps

Transitional Epithelial Cells

• Smaller than squamous, but slightly larger than RTE

• Have centrally located nuclei

• Appear in various shapes: spherical, polyhedral, caudate

• Often have a well-defined edge

• Can be difficult to distinguish from renal tubular epithelial (RTE) cells

• Originate from the lining of the renal pelvis, calyces, ureters, and male urethra

• increased amounts seen in catheterization

Abnormal Transitional Cells

• Vacuoles or irregular nuclei may suggest:

  • Viral infection

  • Malignancy (e.g., bladder cancer)

• Refer to cytology for evaluation

• Stains: Wright’s or Sedi stain

Renal Tubular Epithelial (RTE) Cells

• Smaller than squamous, larger than WBCs

• Shape: cuboidal, columnar, or round (often flattened edges)

• Nuclei are typically eccentrically located

• 0–2/hpf = normal

• >2/hpf = renal tubular damage or necrosis

  • Causes: infection, drug toxicity, heavy metals, allergic reactions

• RTE’s reabsorb filtrate, therefor can take on various colors

  • bilirubin → yellow color

  • Hemosiderin → yllw-brn

Oval Fat Bodies

• RTE cells that have absorbed lipids from glomerular filtrate

• Lipid appears highly refractile; often seen with fat droplets or fatty casts

• Confirm with:

  • Sudan III or Oil Red O (triglycerides/neutral fat)

  • Polarized light (cholesterol → Maltese cross pattern)

• May be confused with starch or crystals

Lipiduria

• Presence of fat in urine

• Confirm with Oil Red O or Sudan III stain

Associated with:

• Nephrotic syndrome (glomerular damage)

• Tubular necrosis

• Diabetes mellitus

• Trauma (bone marrow fat)

• Lipid storage diseases → oval fat bodies from histiocytes (not RTE)

Bacteria in Urine

• Not normally present

• Can multiply at room temp >2 hrs, altering results

• Evaluate microscopy findings alongside nitrite and leukocyte esterase tests

• Presence suggests UTI (upper or lower)

• Follow up: Quantitative urine culture if UTI is suspected

Yeast in Urine

• Small, refractile ovals; may show budding or hyphae

• Common species: Candida albicans

• Often seen in:

  • Diabetes mellitus (acidic, glucose-rich urine)

  • Immunocompromised patients

  • Vaginal yeast infections

• May be a contaminant; rapid growth → interpret with caution

• WBCs should be present if infection is true

• Differentiation tip: Yeast resists acid/base, RBCs do not

Mucus in Urine

• Made by RTEs and lower GU tract glands

• Major protein: Tamm-Horsfall

• Appears as fine, thread-like strands with low refractive index

• Seen better with lowered light at 10x

• More common in females

• No clinical significance, but reported (1+ to 4+)

• May affect strip test values and turbidity

Spermatozoa in Urine

• Oval head, long tail; ~½ size of an RBC

• Not motile in urine (toxic environment)

• Usually not clinically significant, but may cause:

  • False positive protein on strip due to seminal proteins

  • Lab policy variance: some report only with + protein

When to report Sperm

• Underage or elderly females → potential legal/clinical significance

• Causes may include:

  • Specimen mix-up

  • Sexual activity

  • Sexual assault