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 patients with impaired urinary concentrating ability (i.e. diabetes insipidus, 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 negative 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
- Urine dipstick become positive the protein >300-500mg/d
- 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
- ↑ 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.