Chap 10 Urinalysis

• Urinalysis


  The physical, chemical and microscopic analysis of the urine
• Urinalysis


  • May be the earliest test done
  • Simple to perform
  • The information will provide information that reflects a patient's general health
  • Clinical picture of the patient
  • Potential disease
• Urine formation


  1. Urine is a fluid composed of the waste materials of the blood

  2. It is formed in the kidney and excreted from the body by the urinary system
• Urine formation in nephron

  1. Blood enters the glomerulus from the renal circulation through the afferent arteriole and leaves through the efferent arteriole

  2. As blood circulates through the glomerulus, it is filtered into Bowman's capsule

  3. All substances with MW >70kDa will pass through this membrane except fats/protein

  4. This filtration is known as glomerular filtrate

  5. Approximately 180L of glomerular filtrate is produced daily but only 1-2L urine is eliminated from the normal body
• Urine formation in proximal convoluted tubule

  1. Most water in the filtrate is reabsorbed into body

  2. Na+, cl-, bicarbonate, 40-50% urea is reabsorbed passively at this point

  3. Glucose, amino acid, albumin, creatine, pyruvate, lactate and ascorbic acid are actively reabsorbed into the blood

  4. Phosphate however is reabsorbed by the hormonal control and depending on the electrolyte balance of the body fluid
• Urine formation in loop of Henle

  The filtrate looses water & Na+ in descending portion
• Urine formation in distal convoluted tubule

  1. Urinary pH is determined, where hydrogen & ammonium ions may be excreted in exchange for sodium

  2. The remainder of water is reabsorbed under the influence of anti diuretic hormone (ADH)

  3. The filtrate becomes concentrated and acidified as it passes through the tubule

  4. By the time it reaches collecting tubule, the urine pH is ~6
• Urine composition


  • Depends on factors such as diet, nutritional status, metabolic rate, general state of the body and the ability of kidney to function normally
  • Urine composed of 96% water and 4% dissolved substances such as salt, urea (derived from food eaten and waste product of metabolism)
  • Other inorganic subtances present are K, Ca, Mg, NH3,PO4
  • Abnormal constituents include RBC, WBC, fat, glucose, cast, bile, acetone and hemoglobin
  • The average excretion of normal adult ~1200-1500ml
  • Oliguria-decreased urinary output
  • Polyuria-increased output
  • Anuria-little/no output
• Urine volume for routine analysis

  • Minimum: 12ml
  • However 50ml is preferable
• Type of specimen collection

  • Random
  • 24h/timed
  • Clean catch/midstream
  • First morning specimen
  • Catheter
  • Suprapubic Aspiration
• Voided urine


  • Simplest method of collection
  • First morning specimen- stagnant- in low acid base balance (pH) and hypertonic environment
  • Mid stream urine
  • Advantage – readily repeatable, simple procedure
  • Disadvantage – contaminated by genito-female tract
• Catheterised/suprapubic urine


  • Collected when indicated
  • Invasive procedure – cause discomfort
  • High cellularity
  • Advantage: contamination is avoided
  • Disadvantage: high risk of urinary infection, pooled specimen – been in room temp for many hrs – cellular degeneration
• Specimen collection


  1. For routine analysis, urine must be collected in a dry, clean container

  2. For 24hour collection, patient is given a container with preservative. The container do not need to be sterile, only clean & dry

  3. The first specimen of the day is the most concentrated and is the most preferred

  4. Random specimen collection is the easiest & most frequently collected, does not require any special instruction/preparation

  5. Along the process of collection, the specimen may be contaminated from epithelial cells, bacterial, excess mucus/fecal contamination

  6. Way to avoid contamination: clean the genital area, female patient must inform if they are having menses during collection, clean-catch urine procedure-allowing midstream urine to be collected, first-void urine specimen must be discarded

  7. Catheterized specimen-insertion of a tube through the urethra and into the bladder
• Preservatives


  • A urine specimen should be examined no more than 1 hour
  • Urine may be stored in 4-60C for a maximum of 8 hours
  • 24-hour urine collection may require preservative before the collection starts and must be refrigerated between collection
  • No preservative should be added for specimen used for microbiological study
  • The condition of storage & preservatives at the time of collection until testing are important considerations in the clinical lab