Chemical Examination of Urine

• Reagent strips


  Provide a simple, rapid means for performing medically significant chemical analysis of Urine
• Urine tests performed by reagent strips

  • pH
  • Protein
  • Glucose
  • Ketones
  • Blood
  • Bilirubin
  • Urobilinogen
  • Nitrite
  • Leukocytes
  • Specific gravity
• Multistix


  Tradename for reagent strips manufactured by Siemens Medical Solutions Diagnostics
• Chemstrip


  Tradename for reagent strips manufactured by Roche Diagnostics
• Reagent strip brands are specified by instrumentation manufacturers
• Reagent strips


  Chemical-impregnated absorbent pads attached to a plastic strip
• Reagent strip testing methodology

  1. Dip strip completely but briefly into urine specimen

  2. Remove excess urine

  3. Blot edge of strip

  4. Wait specified time

  5. Compare color reactions to manufacturer's chart
• Formed elements like blood cells sink to the bottom and are undetected in an unmixed specimen
• Semiquantitative values


  Trace, 1+, 2+, 3+, or 4+
• Système International units


  Provided by automated reagent strip readers
• Recommended timing for reagent strip reactions

  60-120 seconds, with leukocyte reaction read at 120 seconds
• Good light source is essential for accurate interpretation of color reactions
• Automated reagent strip instruments standardize color interpretation and timing
• Refrigerated specimens must be allowed to return to room temperature before testing
• Excess urine remaining on the strip can cause runover between chemicals
• Time needed for reactions varies between tests and manufacturers
• Quality control for reagent strips

  1. Test with positive and negative controls at least once every 24 hours

  2. Test when opening a new bottle, getting questionable results, or concerned about strip integrity

  3. Record all control results
• Negative control


  Distilled water is not recommended, must use controls designed for the purpose
• Positive control readings should agree with published values by one color block
• Handling and storage of reagent strips

  1. Protect from moisture, volatile chemicals, heat, and light

  2. Store at room temperature below 30°C

  3. Do not use past expiration date

  4. Do not touch chemical pads
• Demonstration of chemically acceptable reagent strips does not rule out inaccurate results
• Pigments like from phenazopyridine can mask color reactions
• Nonreagent strip tests using tablets and liquids are available for confirmation
• Quality control steps for reagent strips

  • Test open bottles with known positive and negative controls every 24 hr
  • Resolve control results out of range
  • Test reagents used in backup tests
  • Perform controls on new reagents and newly opened bottles
  • Record control results and reagent lot numbers
• Reagent strip testing technique

  1. Mix specimen well

  2. Let refrigerated specimens warm to room temperature

  3. Dip strip completely but briefly

  4. Remove excess urine

  5. Compare reaction colors to manufacturer's chart

  6. Perform backup tests when indicated

  7. Be alert for interfering substances

  8. Understand principles and significance of tests
• Urine pH


  No normal values, must consider with other patient information
• Kidneys


  • Major regulators of acid-base content through secretion and reabsorption
• Healthy individuals usually produce slightly acidic first morning urine (pH 5.0-6.0)
• Normal random urine pH can range from 4.5 to 8.0
• Causes of acidic urine

  • Emphysema
  • Hyperventilation
  • Diabetes mellitus
  • Vomiting
  • Starvation
  • Renal tubular acidosis
  • Dehydration
  • Urease producing bacteria
  • Diarrhea
  • Vegetarian diet
  • Escherichia coli
  • High-protein diet
  • Cranberry juice
  • Old specimens
  • Medications (methenamine mandelate, fosfomycin tromethamine)
• Causes of alkaline urine


  • Vegetarian diet
• Cranberry juice


  Produces acidic urine, used as home remedy for bladder infections
• Urine pH does not reach 9 in normal or abnormal conditions
• No known substances interfere with urinary pH measurements by reagent strips
• Reagent strip pH measurement

  Multistix and Chemstrip use methyl red and bromthymol blue indicators to measure pH 5-9 in 0.5 or 1 unit increments
• Runover from adjacent pads can cause falsely acidic pH reading
• Sources of error/interference for pH reagent strip


  • Runover from adjacent pads
  • Old specimens
• Correlations of pH with other tests

  • Nitrite
  • Leukocytes
  • Microscopic
• Proteinuria


  Presence of protein in urine, does not always signify renal disease
• Clinical proteinuria


  ≥ 30 mg/dL (300 mg/L)