Understanding Urine Composition and Analysis

Urine Overview

• Urine is a "fluid biopsy" that provides a fountain of information about the body
• The kidneys are the only organs that can evaluate their functional status noninvasively
• Urine is an ultrafiltrate of plasma, making it useful for evaluating body homeostasis and metabolic disease processes
• Proper urine collection is essential for accurate urinalysis results

Urine Composition

• Urine consists of urea, organic, and inorganic chemicals dissolved in water
  • It may also contain formed elements like cells, casts, crystals, mucus, and bacteria, which can indicate disease
• Urea, derived from protein and amino acid breakdown, accounts for nearly half of the total dissolved solids
• Inorganic solids include chloride, sodium, and potassium
  • Dietary intake greatly influences the concentration of these inorganic compounds
• Other substances in urine include hormones, vitamins, and medications, not part of the original plasma filtrate
• Creatinine, urea, sodium, and chloride are significantly higher in urine than other body fluids
• Protein and glucose should not be present in normal urine

Urine Volume

• Urine volume depends on the amount of water the kidneys excrete, influenced by body hydration
• Normal daily urine output: 600-2000 mL/day
• Average daily urine output: 1200-1500 mL/day
• Night:Day Ratio: 1:2 - 1:3
• Day:Night Ratio: 2:1 - 2:3
• Kidneys excrete 2-3 times more urine during the day than during the night

Factors Affecting Urine Volume

• Fluid intake influences urine volume
• Fluid loss from nonrenal sources (e.g., sweating) affects urine volume
• Variations in antidiuretic hormone (ADH) secretion can impact urine volume
• The need to excrete increased amounts of dissolved solids also affects urine volume
• To identify if a fluid is urine, check for urea and creatinine content
  • These substances have greater concentrations in urine
• Polyuria is an increase in daily urine volume (>2.5 L/day in adults, >2.5-3 mL/kg/day in children)
  • It can be artificially induced by diuretics, caffeine, or alcohol which suppress ADH
  • Associated with diabetes mellitus and diabetes insipidus
• Diabetes mellitus is caused by a defect in insulin production or function that results in increased body glucose
  • The kidneys do not reabsorb excess glucose, requiring excretion of more water to remove the dissolved glucose
  • The urine appears dilute but has a high specific gravity
• Diabetes insipidus results from a decrease in ADH resulting in inadequate body hydration
  • The urine is truly dilute and has a low specific gravity
• Fluid loss in both conditions is compensated by increased ingestion of water (polydipsia).
  • Polyuria accompanied by increased fluid intake is often the first symptom
• Oliguria is decreased urine output (≤400 mL/day for adults, ≤1 mL/kg/day for infants, ≤0.5 mL/kg/day for children) Is seen when the body enters a state of dehydration
• Anuria is the cessation of urine flow
  • Possibly caused by serious kidney damage or flow of blood to the kidneys
• Nocturia is increased nocturnal excretion of urine
• Dysuria is painful urination

Urinalysis Overview

• Urinalysis is a "fountain of foundation"
• Urinalysis encompasses physical, chemical, and microscopic examinations
• A proper specimen collection is an important factor when performing a urinalysis
• Note that if the quality of the urine specimen is compromised, so is the resultant urinalysis
• Good verbal and written communication with each patient in a sensitive and professional manner can ensure the collection of a quality urine specimen
• The ease with which urine specimens are obtained can lead to laxity or neglect in educating the patient and in stressing the importance of a proper collection.

History of Urinalysis

• Analyzing urine was the actual beginning of laboratory medicine
• Early physicians referenced urine study in cave drawings and Egyptian hieroglyphics, using bladder-shaped flasks (MATULA)
• The physicians obtained diagnostic information from color, turbidity, odor, volume, viscosity, and sweetness
• In the 5th Century BCE, Hippocrates wrote a book on "uroscopy"
• In 1140 CE, color charts described the significance of 20 different colors
• Imracticality urinalysis began to disappear from routine examinations.
• 1627 - Compromised credibility because charlatans began offering their predictions to the public for a healthy fee
• 1694 - Chemical testing progressed from "ant testing" and "taste testing" for glucose to Frederik Dekkers's discovery in 1694 of albuminuria by boiling urine.
• 17th Century - The invention of the microscope in the 17th century led to the examination of urinary sediment and to the development by Thomas Addis of methods for quantitating the microscopic sediment
• 1827 - Richard Bright introduced the concept of urinalysis as part of a doctor's routine patient examination
• 1950s - Modern testing techniques rescued routine urinalysis, which has remained an integral part of the patient examination
• Two characteristics account for the continued popularity:
  • Urine is readily available and easily collected
  • Urine provides information, via inexpensive tests, about many of metabolic functions

Explore the components of urine, including urea, organic, and inorganic chemicals dissolved in water. Learn about urine as a 'fluid biopsy' and its role in evaluating body homeostasis and metabolic disease processes. Also covered is the importance of proper urine collection for accurate urinalysis results.