Chemical Examination of Urine Part 1

• Reagent strip


  Consists of chemical-impregnated absorbent pads attached to a plastic strip. Color-producing chemical reaction takes place when absorbent pads comes in contact with the urine specimen. Results are obtained by comparing the color formed on the pads with the color on the chart supplied by the manufacturer. Semiquantitative value: Trace, 1+, 2+,.. Or an estimated of mg/dL
• Before observing physical exam and chemical, you should use an uncentrifuged urine and should be well mixed
• For manual physical and chemical, the specimen should be well mixed as the formed elements sink at the bottom and can possibly cause false negative
• Proper technique when using reagent strips

  1. Dip the reagent strip completely but briefly

  2. Blot the edge of the strip on absorbent paper and hold the strip horizontally while comparing in with color chart
• Why blot the edge of the strip

  To prevent runover of urine to other tests
• Exposing reagent strips to direct sunlight or volatile fumes causes deterioration of the reagents
• Each analyte has a required time for reading the reagent strip
• Refrigerated specimens should be brought to room temperature before testing as certain analytes have enzymatic principles that are active at physiologic temperatures
• Care of reagent strips

  • Store with desiccant in opaque, tightly closed container
  • Store below 30degC; do not freeze
  • Do not expose to volatile fumes
  • Do not use past the expiration date
  • Do not use if chemical pads become discolored
  • Remove the strips immediately prior to use
• Quality control for reagent strips

  1. Check with both positive and negative controls at the beginning of each shift

  2. Check if a new bottle is opened

  3. Check if there are concerns about integrity of the strips

  4. Check if questionable results are obtained

  5. Resolve control results that are out of range by further testing

  6. Be careful of strip reagent interferences
• Non-reagent strip testing procedures using tablets and liquid chemicals are also used
• Tablets in the reagent strip are either extremely hydroscopic or they extremely absorb moisture, that's why they should be kept in tightly closed containers
• Record all control results and reagent lot numbers
• pH

  Along with the lungs, kidneys are the major regulators of acid-base content of the body. Determined by the concentration of Free H ion
• Normal pH ranges

  • Random samples: pH 4.5 - 8.0
  • First Morning Urine: pH 5.0 - 6.0
  • With normal protein diet: 4.5 to 6.5
• Alkaline tides


  Occur after meals, at approximately 2 pm and 8pm
• The pH of freshly excreted urine does not reach 9 in normal or pathologic conditions
• Methods to measure pH

  pH meter, litmus paper or nitrazine paper and reagent strip
• Tubular secretion is a function involved in pH regulation
• Clinical significance of urine pH

  • Respiratory or metabolic acidosis/alkalosis
  • Renal tubular acidosis
  • Renal calculi formation and prevention
  • Treatment of UTI
  • Precipitation/identification of crystals
  • Determination of unsatisfactory specimen
• Causes of acidic urine


  • Emphysema
  • DM
  • Starvation and Dehydration
  • Diarrhea
  • Presence of acid producing bacteria (E. coll)
  • High protein & high meat diet
  • Cranberry Juice
  • Medications
• Causes of alkaline urine


  • Hyperventilation
  • Vomiting
  • Renal Tubular Acidosis
  • Presence of urease producing bacteria
  • Vegetarian diet
  • Old specimens
  • After meals
• pH reagent strip

  Double indicator system using methyl red and bromthymol blue

  
• Interference in pH reagent strip from old specimens and runover from adjacent protein
• pH reagent strip has no known interfering substances
• Normal urine protein levels

  • < 10 mg/dL (for random urine) or 100 - 150 mg/24 hrs (for 24 hour urine)
• Proteins found in urine

  • ALBUMIN - major serum protein
  • TAMM HORSFALL GLYCOPROTEIN produced by the tubules
  • Serum and tubular microglobulins
  • CHONs from prostatic, seminal and vaginal secretions
• Tamm Horsfall Glycoprotein


  The matrix of all casts, also called uromodulin
• Clinical proteinuria

  Indicated at > 30 mg/dL (300 mg/L)
• Categories of proteinuria

  • Prerenal proteinuria
  • Renal proteinuria
  • Postrenal proteinuria
• Prerenal proteinuria


  Presence of protein not associated with the kidney, caused by increased levels of LMW plasma proteins such as Hgb, myoglobin and acute phase reactants. Not indicative of actual renal disease and not detected by reagent strip
• Conditions causing prerenal proteinuria

  • APR - septicemia/severe infection, inflammation
  • Hemoglobin - after hemolytic episode
  • Myoglobin - muscle injury
  • Immunoglobulin paraproteins (monoclonal light chains) in MM and macroglobulinemia
• Bence-Jones Protein (BJP)


  Monoclonal immunoglobulin light chains, abnormal protein found in patients with multiple myeloma
• Screening and confirmatory tests for BJP

  1. Appears/insoluble/Precipitates @ 40 - 60 °C, Disappears/soluble/Dissolves @ 100 °C

  2. Confirmatory Test: Immunofixation Electrophoresis (IEP)
• Renal proteinuria


  Associated with true renal disease, may be the result of damage to the glomerular membrane or tubular dysfunction
• Conditions causing glomerular damage

  • Glumerulonephritis
  • Glumerulosclerosis
  • Minimal change diseases
  • PSGN
  • DM
  • LE
  • Amyloidosis
  • SCA
• Transitory glomerular changes


  • Strenous exercise
  • Fever
  • Dehydration
  • Hypertension
  • Postural proteinuria
• Microalbuminuria


  Low level albuminuria, proteinuria not detected by routine reagent strip, signifies onset of renal complications of DM
• Microalbuminuria is associated with increased risk of cardiovascular disease
• Reagent strip sensitivity for microalbuminuria is 15mg/dL