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

  • 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[1]
      • 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
    • 90% specific but 50% sensitive in detecting gram neg bacteria that converts nitrate to nitrite
    • A positive test suggest bacteria but a negative test cannot rule out UTI
  • Leukocyte Esterase
    • Enzyme within WBC that is released when WBCs lyse
    • 70% sensitive and 50% specific for detecting WBCs (pyuria)
  • 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

See Also

References

  1. Chaudhari PP et al. The Importance of Urine Concentration on the Diagnostic Performance of the Urinalysis for Pediatric Urinary Tract Infection. Ann Emerg Med. 2017 Feb 3. pii: S0196-0644(16)31512-8.

Authors:

Kaoru Itakura