Urine Microscopy -

Urine Microscopy

1️⃣ What is Urine Microscopy?

Urine microscopy is the microscopic examination of urinary sediment after centrifugation of a urine sample.

It identifies:

Cells
Casts
Crystals
Organisms
Debris

2️⃣ Specimen Collection (Very Important for Exams)

Sample Type

Midstream clean-catch urine (preferred)
Catheter sample in ICU
Early morning sample → concentrated → better yield

Processing

Examine within 1 hour
If delay → refrigerate (4°C)
Centrifuge 10–15 mL at 1500–3000 rpm for 5 minutes
Decant supernatant
Resuspend sediment
Examine under:

Low power (10x)
High power (40x)
Phase contrast (best for dysmorphic RBC)

3️⃣ Systematic Interpretation Approach

Always examine in this order:

Cells
Casts
Crystals
Organisms
Miscellaneous

4️⃣ CELLS IN URINE

A. Red Blood Cells (RBCs)

Normal:0–2 RBCs/HPF

Types

Type	Meaning
Isomorphic RBC	Lower tract bleeding
Dysmorphic RBC	Glomerular origin
Acanthocytes	Highly specific for glomerulonephritis

Dysmorphic RBCs → Think:

IgA nephropathy
Post-streptococcal glomerulonephritis
Lupus nephritis
ANCA-associated vasculitis

RBC casts + dysmorphic RBC = Glomerulonephritis unless proven otherwise

B. White Blood Cells (WBCs)

Normal: 0–5 WBCs/HPF

Increased WBC → Pyuria

Causes:

Urinary tract infection
Acute pyelonephritis
Acute interstitial nephritis
Renal tuberculosis

Sterile Pyuria Causes:

TB
STI
Interstitial nephritis
Renal stones
Papillary necrosis

1️⃣ Leukocyte esterase is an enzyme released by neutrophils.
Its presence in urine indicates pyuria (WBCs in urine).

It correlates with:

5 WBCs/HPF on microscopy

Mechanism—Neutrophils in urine → release esterase → dipstick color change.

Parameter	Value (Approx.)
Sensitivity	70–95%
Specificity	60–90%
Negative Predictive Value	High

Interpretation:

LE positive + symptoms → likely UTI
LE negative → UTI unlikely (but not ruled out)

C. Epithelial Cells

1. Squamous Epithelial Cells

Contamination
Poor sample

2. Transitional Cells

Bladder origin
Instrumentation
Malignancy suspicion

3. Renal Tubular Epithelial (RTE) Cells

Very important in ICU

Seen in:

Acute tubular necrosis
Toxic injury
Sepsis AKI

5️⃣URINARY CASTS

Formed in distal tubule & collecting duct from Tamm-Horsfall protein (uromodulin).
Presence = pathology localized to kidney (not lower tract).

Cast Type	Pathophysiology	Classical Associations	Key Exam Pearls
Hyaline Cast	Slow flow, concentrated urine	Dehydration, fever, exercise, diuretics	Can be normal (0–2/LPF)
RBC Cast	Glomerular bleeding → RBC leak into tubule	Glomerulonephritis, vasculitis, malignant HTN	Pathognomonic of glomerulonephritis
WBC Cast	Tubulointerstitial inflammation	Pyelonephritis, AIN	Distinguishes pyelonephritis from cystitis
Renal Tubular Epithelial (RTE) Cast	Tubular injury	ATN, toxins, viral infection	Seen in early ATN
Granular Cast (Fine)	Breakdown of cellular casts	ATN, CKD	Often transitional stage
Granular Cast (Coarse)	Severe tubular injury	ATN	“Muddy brown cast” = ATN
Muddy Brown Cast	Ischemic/toxic tubular necrosis	ATN	ATN until proven otherwise
Fatty Cast	Heavy proteinuria → lipiduria	Nephrotic syndrome	Maltese cross under polarized light
Oval Fat Bodies	Severe proteinuria	Nephrotic syndrome	Not technically a cast but related
Broad Cast	Low nephron flow	Advanced CKD	“Renal failure cast”
Waxy Cast	Chronic stasis	CKD	Indicates chronicity
Hemoglobin Cast	Intravascular hemolysis	Hemolysis, transfusion reaction	Dipstick positive but no RBC
Myoglobin Cast	Rhabdomyolysis	Crush injury, statin toxicity	Pigment nephropathy
Bacterial Cast	Severe infection	Pyelonephritis	Rare but specific
Mixed Cellular Cast	Severe GN	Lupus nephritis, RPGN	Suggests severe inflammation

URINARY CRYSTALS –

🔹 A. Crystals in Acidic Urine (pH < 6)

Crystal	Shape	Clinical Associations
Calcium Oxalate (Dihydrate)	Envelope	Kidney stones
Calcium Oxalate (Monohydrate)	Dumbbell	Ethylene glycol toxicity
Uric Acid	Rhomboid, needle	Tumor lysis syndrome, gout
Amorphous Urates	Brick dust	Concentrated urine
Cystine	Hexagonal	Cystinuria
Tyrosine	Fine needles	Severe liver disease
Leucine	Yellow spheres	Advanced liver failure
Xanthine	Round	Xanthinuria, chemo
Drug Crystals (e.g., Acyclovir)	Needle-like	High-dose IV drugs

🔹 B. Crystals in Alkaline Urine (pH > 7)

Crystal	Shape	Clinical Associations
Struvite (Magnesium Ammonium Phosphate)	Coffin lid	Urease-producing bacteria
Triple Phosphate	Coffin lid	Same as struvite
Calcium Phosphate	Wedge	Renal tubular acidosis
Amorphous Phosphates	Granular	Alkaline urine
Ammonium Biurate	Thorny apple	Old specimen

🔹 C. Crystals Seen in Any pH

Crystal	Clinical Significance
Cholesterol	Nephrotic syndrome
Bilirubin	Liver disease
Sulfonamide crystals	Drug toxicity
Indinavir crystals	HIV therapy

ICU-Specific Crystal Clues

Clinical Scenario	Likely Crystal
ICU cancer patient post-chemo	Uric acid
High anion gap acidosis + AKI	Calcium oxalate
Recurrent stones young male	Cystine
UTI with alkaline urine	Struvite

7️⃣ ORGANISMS

Bacteria

Rods/cocci
Correlate with symptoms

Nitrite Test-Detects bacteria that convert nitrate → nitrite.

Normal urine contains nitrate (from diet).
Some bacteria reduce it to nitrite.

Diagnostic Performance

Parameter	Value
Sensitivity	30–60%
Specificity	>90%

Interpretation:

Nitrite positive = strongly suggests Gram-negative UTI
Nitrite negative ≠ no UTI

LE + Nitrite together → specificity >95%

Yeast

Budding forms
Candida in catheterized ICU patients

Parasites

Trichomonas (motile)

8️⃣ Urine Microscopy in AKI – High Yield Table

Finding	Diagnosis
Bland sediment	Pre-renal AKI
Muddy brown casts	ATN
RBC casts	GN
WBC casts	Pyelonephritis / AIN
Crystals	Toxin / TLS