Urinalysis: What Does It All Mean?

 How to perform test?

  1. Midstream catch is acceptable
  2. Should be examined within 2 hours
  3. Should be refrigerated if not read immediately

Dipstick Urinalysis Discussion

Urine Specific Gravity (USG)

Purpose: urine osmolality and represnts patient's hydration status and concentrating ability of  their kidneys

Normal: 1.003-1.030

Increased USG: glycosuria, SIADH

Decreased USG: diuretic use, DI, adrenal insufficiency, aldosteronism, impaired renal fx

NOTE: if intrinsic renal insufficiency, USG fixed at 1.010

Urinary pH

Purpose: urinary pH reflects serum pH except in renal tubular acidosis (RTA), useful for diagnosis/management of UTIs and calculi

Normal: 4.5-8.0, slightly acidic usually (5.5-6.5)

Alkaline urine: suggest urea-splitting organism

Acidic urine: uric acid calculi

Hematuria

Criteria: 3 or more RBC per HPF in 2 of 3 urine samples

Testing: for peroxidase activity, will be positive in hematuria, myoglobinuria, hemoglobinuria

-if positive: must look at micro to confirm presence of RBCs

Types: glomerular, renal, urologic

Proteinuria

Criteria: >150 mg/day (10-20mg per dL)

-microalbuminuria= 30-150 mg/day (sign of early renal disease)

Normal urinary proteins: albumin, serum globulins, proteins secreted by the nephron

Testing: reagant sensitive to albumin, but can miss low levels of globulins

-Positive results: 5-10mg/dL

-Dipstick results:

  • 1+  =  30 mg/dL
  • 2+  =  100 mg/dL
  • 3+  =  300 mg/dL
  • 4+  =  1,000 mg/dL

Types: transient and persistent

-Transient: temporary change, benign, self-limited (ex: orthostatic proteinuria that results from prolonged standing, but negative U/A after recumbency)

-Positive test: Repeat U/A

-Persistent has 3 types: glomerular, tubular, overflow (see proteinuria)

-Glomerular: albumin primary urinary protein

-Tubular: malfunctioning tubule cells, low-molecular-weight proteins (LMWP) predominate over albumin, rarely exceed 2 g/day

-Overflow: LMWP overwhelm ability of tubules to reabsorb

-Positive test: Perform 24-hour urinary protein excretion or spot urinary protein-creatinine ratio and micro analysis

Glycosuria

Normal: almost completely reabsorbed in proximal tubule
Criteria: occurs at approximately 180-200 mg/dL
Elevated: DM, Cushing's syndrome, liver and pancreatic disease, Fanconi's syndrome

Ketonuria

Normal: not present in urine
Testing: presence of acetic acid through a chemical reaction
Causes: uncontrolled diabetes, pregnancy, carbohydrate-free diets, starvation

Nitrites

Normal: Not present in urine
Testing: bacteria that reduce urinary nitrates to nitrites

-Positive test: can be gram negatives or gram positive organism (neg > pos)

-Indicate significant number (>10,000/mL)

-Negative test: Can�t R/O UTI because non-nitrate reducing organism cause UTIs

-NOTE: nitrite stick sensitive to air exposure: after one week of exposure about 1/3 of strips give false positive

Leukocyte Esterase

Testing: presence of neutrophils

Sterile Pyuria:

-Organisms: Chlamydia and Ureaplasma urealyticum
-Other causes: balantis, urethritis, TB, bladder tumors, viral infx, nephrolithiasis, foreign body, exercise, glomerulonephritis, corticosteroid, cyclophosphamide use

Bilirubin and Urobilinogen

Normal Bilirubin: no detectable amounts

-Unconjugated bili: not water soluble, doesn't pass through glomerulus
-Conjugated bili: water soluble, indicates possible liver dysfunction or biliary obstruction

Normal Urobilinogen: only small amounts

-Urobilinogen: end product of conjugated bili after metabolized by intestine, small amount reabsorbed into portal circulation and filtered by glomerulus

Increased urobilinogen: hemolysis, haptocellular disease

Decreased urobilinogen: antibiotic use, bile duct obstruction

 

Microscopic Urinalysis Discussion

-should be fresh sample of 10-15 mL centrifuged

White blood cells

Normal: <2/hpf (men); <5/hpf (women)

Epithelial cells

  • squamous epithelial cells: if present, suggest contamination
  • transitional epithelial cells: normally present
  • renal tubular cells: suggests renal pathology

red blood cells

Dysmorphic RBCs: suggest glomerular disease

Casts

  • originate from distal convoluted tubule or collecting duct
  • predominant cellular elements define the cast

casts_0.jpg

Tubular cast in renal biopsy.

Crystals

  • Calcium oxalate crystals: retractile square envelope shape, vary in size
  • Uric acid crystals: yellow to orange-brown, diamond- or barrel-shaped
  • Triple phosphate crystals: can be normal, but also associrated with alkaline urine or UTI (Proteus): colorless, coffin lid appearance
  • Cystine crystals: colorless, hexagonal shape, in acidic urine (diagnostic of cystinuria)

Bacteriuria

Gram staining: can guide antibiotic therapy

Criteria (Women):

Asymptomatic Criteria: 5 bacteria/hpf correlates with 100,000 CFU/mL

Symptomatic Criteria: 100 CFU/mL consisten with UTI

Criteria (Men): presence of bacteria suggests infection, should obtain culture

Reference

Simmerville et al. Urinalysis: A Comprehensive Review. American Family Physician. Vol 71 No 6 2005. http://www.aafp.org/afp/20050315/1153.html

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