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Urine is a mixture of urea, a by-product of the digestion of proteins, and water. All vertebrates, including human beings, produce urine as a waste product. Urine is produced in the kidneys, and is stored in the bladder until it is expelled through the urethra.

Urine can be an important diagnostic tool for doctors, and the failure to process urine normally can indicate a serious disorder. Although the urea in urine sterilizes anything mixed in with it, other proteins or cells in the urine can be evidence of a serious disorder.

If a patient is unable to urinate, either due to a blocked urethra or some other cause, the kidneys will fail and the urea that is usually processed by the kidneys will be released back into the blood. In addition, the inability to expel water through urine can lead to edema, where fluids gather in the body's tissues, causing them to swell. Patients who are on intravenous fluids often have to have their urine production monitored as well.

In the normal human body, urine production is based on the amount of water consumed, minus any water lost through sweat or the digestive tract. The body can generally concentrate or dilute the urea in the kidney based on the amount of water consumed.


Urinalysis is the physical, chemical, and microscopic examination of urine. It involves a number of tests to detect and measure various compounds that pass through the urine.

A sample of urine is needed. The doctor will tell the patient what type of urine sample is needed. Then the sample is analyzed in the laboratory

How it's done[]

The urinalysis composes of three phases: physical, chemical and microscopic.

  • Physical analysis: In the physical analysis, three characteristics of the urine are noted: color, appearance, and specific gravity. The urine can be classified as clear, hazy or cloudy. The specific gravity is measured with a refractometer.
  • Chemical analysis: In the chemical analysis, a dipstick is inmersed in the urine, then it's compared to a color standard in the dipstick's bottle. Usually, dipsticks measure between 8 to 10 parameters, these are:
    • White blood cells: This should be confirmed with microscopic presence of WBCs in the urine.
    • Nitrite
    • Urobilinogen
    • Protein: This should be confirmed with sulfosalicylic acid (SSA) test (a portion of urine sample is placed in a tube to which SSA is added. If protein is present, the urine will turn cloudy or turbid).
    • pH
    • Blood: This should be confirmed with microscopic presence of RBCs or urinary casts in the urine.
    • Specific gravity: This is better measured with refractometer.
    • Ketone: This should be confirmed with Acetest (urine drops are added to a Clinitest test table. If ketones are present, a purple color will appear).
    • Bilirubin: This should be confirmed with Ictotest (urine drops are added to an Acetest table. If bilirubin is present, a purple color will appear).
    • Glucose: This should be confirmed with Clinitest (a Clinitest tablet is dipped in the urine, and after a determinated time, the color of the urine is compared with a color standard).
  • Microscopic analysis: Urine is poured in a test tube, then is centrifugated. The clear part after the centrifugation (supernatant) is poured off and a portion of sediment (the remaining solid part in the bottom) is placed in a microscope slide. Then, the urine is analyzed for these elements:
    • Cells: White and red blood cells.
    • Bacteria: Cocci (bacteria with spherical shape) and bacillus (rod-shaped bacteria).
    • Urine crystals
    • Urinary casts: Tiny tube-shaped particles made up of white blood cells, red blood cells, or kidney cells. They form in kidney structures called tubules. Casts are held together by a protein released by the kidney. They are:
      • Fatty casts
      • Granular casts
      • Hyaline casts
      • Red blood cell casts
      • Renal tubular ephitelial casts
      • Waxy casts
      • White blood cells

​Interpretation of results[]

  • Color
    • Colorless: Very diluted urine; diabetes insipidus; chronic renal disease
    • Straw to yellow: Normal color
    • Dark yellow/amber: Very concentrated urine; first-morning specimen; vomiting, excess fluid loss, or excesive exercise (the result of dehydration)
    • Orange: Antibiotics used to treat urinary tract infections (UTIs)
    • Cloudy pink, red, or reddish/brown:
      • Hematuria: Intact red cells present in the urine; menstrual contamination
      • Hemoglobinuria: Red cells have ruptured and hemoglobin has been released into the urine
    • Yellow/brown or yellow/green: Bilirubin present; bilirubin converted to biliverdin
    • Green or blue/green: UTI caused by Pseudomonas bacteria; antidepressants such as Amitriptiline; Clorets
    • Brown: RBCs oxidized to methemoglobin; should see a positive test for blood
    • Black: Presence of melanin pigment; homogentisic acid seen after urine stands; certain antihypertensives; Flagyl (an antibiotic)
  • Chemical
    • pH (Normal value: 4.5–8.0): Old specimen; UTI
    • Protein (Normal value: negative/trace): Renal disease; extreme exercise; high fever; dehydration
    • Glucose (Normal value: negative): Diabetes; pancreatic disease; advanced kidney disease
    • Ketones (Normal value: negative): Negative Starvation; low-carbohydrate/high-fat diet; uncontrolled diabetes
    • Blood (Normal value: negative): Hemolytic anemias; kidney or urinary tract damage; menstrual contaminant
    • Bilirubin (Normal value: negative): Hepatitis; possible bile duct obstruction
    • Urobilinogen (Normal value: 0.1–1.0): Liver dysfunction; hemolytic diseases
    • Nitrite (Normal value: negative): UTI; cystitis; used to monitor antibiotic therapy
    • Leukocytes (Normal value: negative): UTI
    • Specific gravity (Normal value: 1.005–1.030): Kidney function; diabetes
  • Microscopic
    • Hematuria: associated with kidney stones, infections, tumors and other conditions
    • Pyuria: associated with urinary infections
    • eosinophiluria: associated with allergic interstitial nephritis, atheroembolic disease
    • Red blood cell casts: associated with glomerulonephritis, vasculitis, malignant hypertension
    • White blood cell casts: associated with acute interstitial nephritis, exudative glomerulonephritis, severe pyelonephritis
    • (heme) granular casts: associated with acute tubular necrosis
    • crystalluria: associated with acute urate nephropathy (or "Acute uric acid nephropathy", AUAN)
    • calcium oxalatin: associated with ethylene glycol toxicity

Common serious symptoms and causes[]

Inability to urinate, or sporadic urination - swollen prostate gland in males.

Frequent urination with sugar in urine - diabetes mellitus.

Frequent urination without sugar in urine, very dilute urea - diabetes insipidus.

Blood in urine - infection of the bladder or urethra, often by a sexually transmitted disease.

White blood cells in urine - serious systemic infection.