Urine analysis

Reference Range

Color	Yellow
Clarity/turbidity	Clear
pH	4.5-8.0
Specific gravity	1.005-1.025
Glucose	<130 mg/d
Ketones	None
Nitrites	Negative
Leukocyte esterase	Negative
Bilirubin	Negative
Urobilirubin	Small amount (0.5-1mg/dL)
Blood	<3 RBCs
Protein	<150mg/d
RBCs	<2 RBCs/hpf
WBCs	<2-5 WBCs/hpf
Squamous epithelial cells	<15-20 per hpf
Casts	0-5 hyaline casts/hpf
Crystals	Occasionally
Bacteria	None
Yeast	None

Collection

• Midstream urine specimen should be collected in clean container
• Women should clean external genitalia before voiding to avoid contamination
• Urine specimen should be analyzed within 30-60min for accurate results

Analysis

Gross Visual Examination

• Color
  • Normal color varies from pale light yellow to dark amber
  • See Abnormally colored urine

• Clarity/turbidity
  • Determined by substances in urine, including cellular debris, casts, crystals, bacteria, proteinuria, vaginal discharge, sperm

Chemical Examination

• pH
  • Slightly acidic urine is normal
  • Any acid-base abnormalities affects urinary pH
  • Diet can affect pH
  • Useful in evaluation stones, infection, RTA
    • Stones: alkaline (calcium/oxalate/calcium phosphate, magnesium-ammonium phosphate, staghorn) vs acidic (uric acid, cysteine)
    • UTI: proteus and klebsiella produce alkaline urine

• Specific gravity
  • Represents kidney's ability to concentrate urine; often reflective of hydration status
  • Low values can be seen in pts with impaired urinary concentrating ability (i.e. diabetic insidious, sickle cell nephropathy, acute tubular necrosis)
  • High values can be due to elevated protein or ketoacids
  • Specific gravity should be considered in detection of pediatric UTI
    • The higher the concentration of the urine, when in the presence of negative LE, the higher the negative predictive value of UTI
    • At threshold of greater than or equal to 5 WBCs per HPF in microscopic UA

• Glucose
  • Glucosuria is due to high blood glucose or decreased kidney threshold concentration
  • Typically seen in diabetics or pregnant patients

• Ketones
  • Typically seen with uncontrolled diabetes, Diabetic ketoacidosis, severe exercise, starvation, vomiting, pregnancy

• Nitrite
  • Specific but not sensitive in detecting Acute cystitis
    • A positive test suggest UTI but a negative test cannot rule out UTI

• Leukocyte Esterase
  • Enzyme within WBC that is released when WBCs lyse
  • Typically implies Acute cystitis

• Bilirubin
  • Increased urobilirubin associated with excessive hemolysis, liver disease, constipation, intestinal bacterial overgrowth
  • Decreased urobilirubin associated with obstructive biliary disease and severe cholestasis

• Proteins
  • Urine dipstick become positive the protein >300-500mg/d
    • Trace - 10-30mg/dl
    • 1+ - 30mg/dl
    • 2+ - 100mg/dl
    • 3+ - 300 mg/dl
    • 4+ - >1000mg/dl
  • Etiology
    • Transient proteinuria: CHF, fever, exercise, seizure, stress
    • Persistent proteinuria: nephrotic syndrome, glomerulonephritis, ATN, AIN, Falcon syndrome, multiple myeloma, myoglobinuria

• Blood
  • If more than 3RBCs, urine dipstick is positive for blood
  • Does not detect where the blood is coming from
    • Can be due to hematuria, hemoglobinuria, myoglobinuria, contamination
    • Blood+/RBC+ → hematuria
    • Blood+/RBC- → myoglobinuria (rhabdomyolysis, renal failure) or hemoglobinuria (infection, transfusion-related reaction, paroxysmal nocturnal hemoglobinuria)

Microscopic Examination

• WBCs
  • Elevated WBCs indicate infection, inflammation or contamination

• RBCs
  • Microscopic hematuria defined as 3RBCs/hpf or more
  • Transient hematuria in young patients is typically benign. In older patients >50yo, warrants further work-up for underlying malignancy
  • Persistent hematuria always warrants further work-up
    • Renal: glomerular (proteinuria, RBC casts, dysmorphic RBCs) vs nonglomerular (no RBC casts or dysmorphic RBCs)
    • Extrarenal: tumors, stones, BPH, infections (pyelonephritis, cystitis, prostatitis, urethritis), schistosomiasis, foley trauma, anticoagulants, chemotherapy

• Epithelial Cells
  • Generally, 15-20 squamous cells or more indicates contamination
  • Hyaline casts - nonspecific
  • Red cell casts - nearly diagnostic of glomerulonephritis or vasculitis
  • White cell casts - tubulointerstitial nephritis, acute pyelonephritis, renal tuberculosis, vaginal infection
  • Muddy-brown granular casts - diagnostic of acute tubular necrosis
  • Waxy and broad casts - advanced renal failure
  • Fatty casts - nephrotic syndrome

• Crystals
  • May be normal
  • Calcium oxalate crystals - ethylene glycol ingestion
  • Uric acid crystals - tumor lysis syndrome, gout
  • Cystine crystals - cystinuria
  • Magnesium ammonium phosphate and triple phosphate crystals - UTI caused by Proteus, Klebsiella

• Bacteria
  • Generally due to infection or contamination
  • If positive for nitrites, leukocyte esterase and bacteria - highly suggestive of UTI
  • If significant amount of squamous epithelial cells - may indicate contamination
  • Urine culture should be obtained if UTI suspected
    • Generally, >100K/mL of a single organism reflects significant bacteriuria

• Yeast
  • Generally due to infection or contamination

References

• Edgar, L. emedicine.medscape.com/article/2074001

Authors

Kaoru Itakura