Urine Glucose Reagent Strip Parameters

Quality Control for Reagent Strips

• Run quality control when opening a new bottle or when obtaining questionable results
• Manual methods can be done using tablets or liquid chemicals when questionable results are obtained or when the urine is highly pigmented

Urine Glucose

• Double sequential enzymatic reaction involves two enzymes: glucose oxidase and peroxidase
• Reagent strip contains a mixture of glucose oxidase, peroxidase, chromogen (indicator), and buffer
• Procedure:
  • Mix urine specimen thoroughly
  • Never allow strip to remain in urine for extended periods
  • Never forget to blot the edge of the strip after dipping
  • Compare color reactions of the dipstick with the color chart horizontally
  • Use good light source
  • Never interchange reagents strips and color charts from different manufacturers
  • Allow refrigerated specimen to return to room temperature before using reagent strips
  • Protect reagent strips from deterioration caused by moisture, volatile chemicals, heat, and light
  • Store at room temperature below 30°C, but never refrigerated
  • Never use past the expiration date

Reaction Interferences

• False (+) results can occur due to:
  • Hydrogen peroxide
  • Urine container contaminated with detergents
• False (-) results can occur due to:
  • Ascorbic acid
  • High level of ketones
  • High specific gravity of urine
  • Low temperature
  • Prolonged standing of urine

Copper Reduction Tests for Glucose

• Rely on the ability of glucose and other reducing substances to reduce copper sulfate to cuprous oxide in the presence of alkali and heat
• Color change from negative blue to green, yellow, orange, and red
• Tests that utilize this principle:
  • Benedict's Test
  • Copper sulfate
  • Sodium carbonate
  • Sodium citrate buffer

Chemical Examination of Urine

• Chemical examination of urine validates physical aspects of urine analysis
• Reagent strips (dipsticks) are a sensitive and rapid procedure
• Reagent strip:
  • Narrow strip of plastic with small pads attached to it
  • Each pad contains reagents for different reactions, allowing for simultaneous determination of several tests
  • Colors generated are compared against a brand-specific color chart

Technique for Using Reagent Strips

• Dip reagent strip briefly into well-mixed urine at room temperature
• Remove excess urine by touching the edge of the strip to the container upon withdrawal
• Blot the edge of the strip into an absorbent pad
• Wait for the specified amount of time
• Compare the color reaction of each pad to the manufacturer's color chart
• Run with positive and negative controls every 24 hours at the beginning of each shift

Urine Protein

• Protein error indicators:
  • Tetrabromphenol blue
  • Tetrachlorophenol or Tetrabromsulfonphthalein
• Acidic buffer maintains pH of indicators at 3.0, giving them yellow coloration in the absence of proteins
• Proteins (primarily albumin) accept hydrogen ions from the indicator, altering the pH and turning the color from yellow to green to blue, depending on the amount of proteins
• Color is reported in terms of negative, trace, 1+, 2+, 3+, 4+

Renal Proteinuria

• Glomerular proteinuria:
  • Selective filtration is impaired due to damage in glomerulus (e.g., lupus, erythematosus, and streptococcal glomerulonephritis)
• Tubular proteinuria:
  • Tubular dysfunction (e.g., heavy metal poisoning, Fanconi syndrome, and viral infection)
• Microalbuminuria:
  • Development of diabetic nephropathy and cardiovascular disease
• Orthostatic/postural proteinuria:
  • Physiologic type due to prolonged standing, increased glomerular pressure, and ability of proteins to cross over
  • Common in jobs that require prolonged standing