Urinalysis Chemical and Microscopic Examination

Urinalysis - Chemical Examination

• Urine reagent strips are used to rapidly screen urine for various chemical components.
• Ictotest reagent tablets are used to test for bilirubin in urine, an indicator of liver disease.
• Refractometers (manual and digital) are used to measure urine specific gravity (SG) and assess hydration status.

Urinalysis - Microscopic Examination

• Microscopic urinalysis involves examining a urine sample under a microscope to identify cells, crystals, casts, and other substances.

Quality Control

• Quality control must be performed daily using known positive and negative controls to ensure the accuracy of urinalysis tests.
• Commercially available controls with set values for the test being performed are used.
• QC data is recorded daily, including the date a strip or bottle is opened, the expiration date, and storage information.
• If quality control fails, the test cannot be performed and must be troubleshooted.

Post-Analytical Variability

• Post-analytical variability focuses on the final inspection of results before reporting or releasing to the provider.
• Barcoded ID systems help prevent misidentification and inaccurate labeling.
• Automated transmission of reports ensures results are shared promptly.
• A troubleshooting plan can identify and prevent errors.

Renal Anatomy

• The renal system consists of two kidneys, two ureters, one bladder, and one urethra.

Renal Physiology

• The nephron is the functional unit of the kidney, where urine is formed.
• Formed urine flows from the kidney into the ureters and is stored temporarily in the bladder.
• Urine is eliminated from the body through the urethra.

Functions Of The Kidneys

• Main functions of the kidneys:
  • Removal of waste products
  • Retention of nutrients
  • Acid-base balance
  • Water and electrolyte balance
  • Hormone synthesis

Histology of The Renal System

• Epithelial cells line all urinary system structures, each with a specific type.
• Transitional epithelial cells line the bladder and ureters.
• Squamous epithelial cells are primarily found in the urethra.
• Renal tubular epithelial cells originate from the kidney tubules.

Types of Urine Specimens

• Random specimen: collected at any time.
• First morning specimen: collected upon waking.
• Midstream clean-catch specimen: collected after cleaning the genital area, with the middle portion of the stream collected.
• 24-hour or timed specimen: urine collected over a 24-hour period.
• Catheter collection specimen: collected using a catheter.
• Suprapubic aspiration specimen: collected by inserting a needle directly into the bladder.
• Pediatric specimen: collected using a urine bag.

Collection and Preservation of Urine Specimens

• Containers for urine collection:

  • Urine collection cups
  • Urinalysis tubes
  • 24-hour collection containers
  • Urine culture containers
  • Urine transport tubes

• Minimum volume for routine urinalysis: 12 mL, but 50 mL is preferable.

• Urine for microscopic analysis: Centrifuged and concentrated to 1 mL of sediment.

Collection of Urine Specimens

• Routine specimens: Fresh, clean, dry container.
• Timed urine specimens: Patient is instructed about collection process.
• Urine for culture: Clean-catch, midstream specimen.

Preservation of Urine Specimens

• Urine decomposition begins within 30 minutes after collection.
• Refrigeration is the best method of preservation.
• Chemical preservatives include hydrochloric acid, boric acid, and acetic acid.

Labeling and Processing Urine

• Labels: Date and time of collection, collection method (UV/UC/Random), preservation, light protection.

Physical Properties of Urine

• Volume: Normal adult range: 1200-1500 mL/24 hours.
• Color: Determined by pigments: urochrome, uroerythrin, and urobilin.
• Transparency: Normally clear, can become cloudy when it stands.
• Odor: Faintly aromatic.
• Specific Gravity: Measures dissolved substances in urine compared to distilled water.

Abnormal Volumes

• Polyuria: More than 2000 mL/24 hours.
• Diuresis: Any increase in urine volume.
• Oliguria: Less than 500 mL/24 hours.
• Anuria: Complete absence of urine formation.
• Nocturia: Excretion of more than 400 mL urine at night.

Abnormal Color

• Pale: Dilute urine.
• Amber: Concentrated urine or bilirubin.
• Brown: Bilirubin or biliverdin.
• Orange: Urobilin, azo-containing dyes or compounds.
• Red: Blood, heme-derived pigments, urates, drugs, foodstuffs.
• Clear red: Hemoglobin.
• Cloudy red: Red blood cells.
• Dark red-brown: Myoglobin.
• Dark red or red-purple: Porphyrins.
• Black or dark brown: Melanin, homogentisic acid, phenol poisoning.
• Green, blue, or orange: Drugs, medications, foodstuffs.

Abnormal Transparency

• Hazy, cloudy, turbid: Mucus, phosphates, urates, crystals, bacteria, pus, fat, casts.

Abnormal Odor

• Ammonia (ammoniacal): Breakdown of urea by bacteria (old urine).
• Sweet or "fruity": Ketone bodies.
• Other abnormal odors: Infection, specific amino acid disorders.

Specific Gravity

• Clinically important for assessing kidney function and hydration status.
• Reagent strips are commonly used to measure specific gravity.

Chemical Tests in Routine Urinalysis - Reagent Strip Tests

• Advantages: Convenience, cost-effectiveness, stability, ease of use, disposability, smaller sample volumes, space savings.
• Timing: Follow manufacturer's instructions for each test.
• Automated instruments: Control exact timing of chemical reactions.

Chemical Tests in Routine Urinalysis - Reagent Test Strips - pH

• Clinical importance: Kidneys eliminate excess acid.
• Acidic urine: Causes and effects.
• Alkaline Urine: Causes and effects.
• Reagent strip tests: Principle: Double-indicator system (methyl red and bromthymol blue).
• Additional comments: Test fresh specimens to avoid pH shift due to bacterial growth, avoid excessive wetting of the strip.

Chemical Tests in Routine Urinalysis - Reagent Test Strips - Protein

• Clinical importance: Proteinuria can indicate glomerular or tubular damage.