Chap 11 Physical & Chemical Properties Use of Urine

• Abnormal constituents are found in the subsequent tests because abnormal physical and chemical properties were noted
• Volume


  Normal adult with normal fluid intake: 1200ml-1500ml
• Abnormal urine volume


  • Polyuria: consistent elimination of an abnormally large volume of urine (>2L/24hr)
  • Diuresis: Any increase in urine volume, even if the increase is only temporary
  • Oliguria: Excretion of abnormally small amount of urine (<500ml/24hr)
  • Nocturia: Excretion of more than 400ml urine at night
• Colour


  • Normal color of urine ranges from pale yellow to deep amber
  • The colour of the urine is the result from the pigments of: Urochrome, urobilin & uroerythrin
• Examples of Urine Color

  • Pale
  • Amber(dark yellow @ orange-red)
  • Brown (yellow brown or green-brown)
  • Orange (Orang-red or orange-brown)
  • Bright orange
  • Red
  • Clear red
  • Cloudy red
  • Dark-red brown
  • Dark red or red purple
  • Black (dark brown and black)
  • Green,blue or orange
• Transparency


  • Fresh urine is normally clear after collection
  • Upon standing normal acidic urine become cloudy/turbid (due to normal precipitation of amorphous urates-give urine a pink hue)
  • If the pH is basic/alkaline, white amorphous phosphates may precipitate(normal)
• Examples of Urine Clarity

  • Clear: No visible particulate matter present
  • Hazy/slightly cloudy: Some visible particulate matter present; newsprint is not distorted when viewed through urine
  • Cloudy: Newsprint can be seen through the urine, but letters are distorted/blurry
  • Turbid: Newsprint cannot be seen through the urine
• Odour


  • Normal urine: an aromatic odour which will acquire an ammonia odour upon standing due to the breakdown of urea
  • Detecting the odour may be helpful in early detection of disease (maple syrup urine disease-an inherited metabolic disorder)
• Specific gravity


  • Ratio of the weight/density of a solution(urine), to an equal amount of water which has a specific gravity of 1.000
  • Normal healthy individual will range from 1.015-1.025
• Specific gravity conditions


  • High SG (hyperstenuria) may results from conditions that cause dehydration
  • Extremely high SG (>1.035) associated with patient undergone procedures that required the used of diagnostic imaging procedures
  • Low SG(<1.010) indicates hypothenuria (kidney has lost the ability to concentrate urine)
  • Certain diseases directly affecting the kidney that may result in hypothenuria are pyelonephritis & glomerulonephritis
  • Diabetes insipidus (not a kidney disease) may result in urine with low SG
• Methods to measure specific gravity

  1. Urinometer: Measure SG through specially designed weight float which is suspended in urine

  2. Refractometer: Measure the refractive index, which is the comparison of the speed of light in air with the speed of light in a solution

  3. Reagent strips: Chemical method and is not as sensitive as the two physical methods
• Chemical examination


  • Reagent strips(dipstick) are used for analyzing chemical examination of urine
  • Used only once and discarded
  • Each pad is designed to perform different chemical analysis which will produce a colour reaction after coming into contact with a particular substance in urine
  • The result will be compared to a chart provided on the reagent bottle to determine the result
  • Strips must not exposed to temperature >300C(RT recommended)
  • Testing: Perform within 1 hour after collection, Allow refrigerated specimens to return to room temperature, Dip strip in fresh urine and compare color of pads to the color chart after appropriate time period, Instruments are available which detect color changes electronically
• Reagent Strips


  • BRIEFLY dip the strip in urine
  • Colors are matched to those on the bottle label at the appropriate times
  • Timing is critical for accurate results
• Glucose


  • Presence of glucose (glycosuria) indicates that the blood glucose level has exceeded the renal threshold
  • Useful to screen for diabetes
  • Other possibilities of glycosuria: Hypothyroidism, Reduced glomerular blood flow, Reduced tubular reabsorption, Reduced urine flow
• Bilirubin


  • Bilirubin is a byproduct of the breakdown of hemoglobin
  • Normally contains no bilirubin
  • Presence may be an indication of liver disease, bile duct obstruction or hepatitis
  • Exposure of the urine samples to light for a long period of time may result in a false negative test result
• Ketones


  • Ketones are excreted when the body metabolizes fats incompletely (ketonuria)
  • Associated with low urinary pH
  • Occur during starvation and DM
• Specific Gravity


  • Specific gravity reflects kidney's ability to concentrate
  • Concentrated urine for accurate testing (best is the first morning sample)
  • Low – specimen not concentrated, kidney disease
  • High – first morning, certain drugs
• Blood


  • Presence of blood may indicate infection, trauma to the urinary tract or bleeding in the kidneys
  • False positive readings most o
• Glycosuria


  • Hypothyroidism
  • Reduced glomerular blood flow
  • Reduced tubular reabsorption
  • Reduced urine flow
• Bilirubin


  • Byproduct of the breakdown of hemoglobin
  • Normally contains no bilirubin
  • Presence may be an indication of liver disease, bile duct obstruction or hepatitis
  • Sensitive to light, exposure may result in false negative test result
• Ketones


  • Excreted when the body metabolizes fats incompletely (ketonuria)
  • Associated with low urinary pH
  • Occur during starvation and DM
• Specific Gravity


  • Reflects kidney's ability to concentrate
  • Concentrated urine for accurate testing (best is the first morning sample)
  • Low - specimen not concentrated, kidney disease
  • High - first morning, certain drugs
• Blood


  • Presence may indicate infection, trauma to the urinary tract or bleeding in the kidneys
  • False positive readings most often due to contamination with menstrual blood
  • False negative maybe due to lysis of RBCs, hypertension, ascorbic acid interference, high specific gravity
• pH


  • Measures degree of acidity or alkalinity of urine
  • Normal pH??
  • pH below 4.5/above 8.0 is probably an indication of an improper collected/stored sample and may be not suitable for further testing
  • Reactions will be based on the reaction of colour indicators with H+ in the urine
  • Urinary pH is important in identifying crystals (uric acid)
  • The formation of various types of kidney stones is strongly influenced by urinary pH
  • Acidic urine-starvation, DM, respiratory disorder
  • Alkaline urine-prolonged vomiting, vegetarian diet
• Protein


  • Presence of protein (proteinuria) is an important indicator of renal disease
  • False negatives can occur in alkaline or dilute urine or when primary protein is not albumin
  • Normal urine-contain small amount of albumin
  • If damage occur in the glomerular membrane, there will be increase amount of protein in urine
  • Conditions that may cause glomerular damage: Acute glomerulonephritis, Toxins, Immunologic reactions, infections
  • Other sources- may be from prerenal (lower urinary tract)
  • Prerenal condition that result in protein production-multiple myelome
  • Non-pathologic conditions-orthostatic proteinuria( patient changing postural position from lying down to sitting/standing)
• Urobilinogen


  • Degradation product of bilirubin formed by intestinal bacteria
  • May be increased in hepatic disease or hemolytic disease
• Nitrite


  Formed by gram negative bacteria converting urinary nitrate to nitrite
• Leukocyte esterase


  • Leukocytes (white blood cells) usually indicate infection
  • Leucocyte esterase activity is due to presence of WBCs in urine while nitrites strongly suggest bacteriuria
• Normal Values


  • Colour: Yellow
  • Transparency: Clear
  • pH: 5-7
  • Specific gravity: 1.001-1.035(adult)
  • Blood/haemoglobin: Negative
  • Nitrite: Negative
  • Leukocyte esterase: Negative
  • Glucose: Negative
  • Ketones: Negative
  • Bilirubin: Negative
  • Urobilinogen: <1mg/dl
  • Protein/albumin: Negative/trace(in concentrated urine)
• Handling and Storage of Strips

  • Keep strips in original container
  • Do not touch reagent pad areas
  • Reagents and strips must be stored properly to retain activity: Protect from moisture and volatile fumes, Stored at room temperature
  • Use before expiration date
• Procedure


  1. Dip strip briefly, but completely into well mixed, room temperature urine sample

  2. Withdraw strip

  3. Blot briefly on its side

  4. Keep the strip flat, read results at the appropriate times by comparing the color to the appropriate color on the chart provided
• Sources of Error


  • Timing - Failure to observe color changes at appropriate time intervals may cause inaccurate results
  • Lighting - Observe color changes and color charts under good lighting
  • QC - Reagent strips should be tested with positive controls on each day of use to ensure proper reactivity
  • Sample - Proper collection and storage of urine is necessary to insure preservation of chemical
  • Testing cold specimens - would result in a slowing down of reactions; test specimens when fresh or bring them to RT before testing
  • Inadequate mixing of specimen - could result in false reduced or negative reactions to blood and leukocyte tests; mix specimens well before dipping
  • Over-dipping of reagent strip - will result in leaching of reagents out of pads; briefly, but completely dip the reagent strip into the urine
• Automation


  • Dip sticks rarely, if ever, read by hand
  • Automated readers automatically reads a urine dipstick and prints out results
  • Increases accuracy of results
• A 28 year old man visits his physician complaining of an intense, sharp pain in his back and side. In a conversation with his physician, the patient confesses to eating a diet high in animal proteins such as meat, cheese, and fish. Results of a complete urinalysis are shown.
• For years, a 55-year-old white female has had significant trouble with keeping her diabetes mellitus and hypertension under control. Recently, she arrived at the Emergency Room with complaints of severe weakness, nausea and vomiting
• Physical properties of urinalysis

  • Volume
  • Colour
  • Transparency
  • Odour
  • Specific gravity
• Chemical properties of urinalysis

  • SG
  • Glucose
  • pH
  • Ketone
  • Bilirubin
  • Urobilinogen
  • Protein
  • Nitrite
  • Leukocyte esterase