Urine

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Yazan Daaboul, M.D. Synonyms and keywords: Urinary findings; Urinary abnormalities; Findings on urine exam; Urine; Urine composition; Urine output

Overview

Urine is a fluid produced by humans through the kidney, collected in the bladder, and excreted through the genital urethra. Urine formation helps to maintain the balance of minerals and other substances in the body. Urinary findings may be qualitative or quantitative. Qualitative urinary findings are often analyzed on urinalysis and urine culture. Quantitative urinary findings depends on urine output.

Urinary Findings Algorithm

Urinary Findings

Quality (Composition)

Quantity

Urinalysis

Urine culture

Urine output

High urine output

Low urine output

Urine odor

Urine color and turbidity

Specific gravity/osmolality

Urinary pH

Hematuria

Pyuria

Proteinuria

Cells

Casts and Crystals

Other

Polyuria

Oliguria

Anuria

Urine Odor

Urine is usually odorless but can produce pungent smells following the consumption of certain foods (e.g. asparagus)

Urine Color and Turbidity

Color

Below is a list of common urine discolorations and their associated diseases.

• Clear or light yellow
  • Normal urine color (caused by the pigment urochrome and degradation of bilirubin and urobilin products)
• Dark yellow
  • Dehydration
• Greenish yellow color
  • Vitamin B ingestion
• Orange color
  • Excess urinary losses of vitamin B
  • Medication-induced: rifampin and pyridium
• Dark red color
  • Hematuria
  • Myoglobinuria
  • Ingestion of certain foods: berries, colored candy, and beets
• Brown color
  • Hematuria
  • Myoglobinuria
  • Porphyria
  • Hyperbilirubinemia
• Black (melanuria)
  • Sarcoma
  • Alkaptonuria

Turbidity

• Normal urine is usually clear
• Turbid urine may be a manifestation of urinary bacterial infection, hematuria, proteinuria, pyuria, or presence of crystals and casts.

Urine Specific Gravity and Osmolality

Urine Specific Gravity

• Normal urine specific gravity (density) ranges between 1.003 and 1.035 g.cm^-3.
• Specific gravity outside the normal range may sometimes be associated with urinary disorders.

Urine Osmolality

• In healthy individuals with restricted fluid intake, urine osmolality should be > than 800mOsm/kg.
• 24-hour urine osmolality normally ranges between 500 and 800 mOsm/kg.
• Random urine osmolality normally ranges between 50 and 1400 mOsm/kg.

Increased urine osmolality

• Acidosis
• Addison's Disease
• Congestive Heart Failure
• Hepatic cirrhosis
• Hypernatremia
• Shock
• Syndrome of Inappropriate Anti Diuretic Hormone (SIADH)

Decreased urine osmolality

• Aldosteronism
• Amyloidosis
• Chronic Interstitial Nephritis
• Chronic pyelonephritis
• Diabetes Insipidus
• Primary polydypsia
• Glomerulonephritis
• Hypercalcemia
• Hypokalemia
• Lithium nephrotoxicity
• Nephrogenic diabetes insipidus
• Polycystic kidneys
• Renal Tubular Necrosis

Urinary pH

• The pH of urine is normally close to neutral pH=6-7 (Range: 4.5 to 8.2).
• Strongly acidic or alkaline urine may be manifestations of the following:

Renal and urologic diseases

• Urinary tract infection
• Acute kidney injury
• Chronic kindey disease
• Renal tubular acidosis

Systemic diseases

• Diabetes Mellitus
• Diarrhea
• Vomiting
• Fanconi's Syndrome
• Increased protein catabolism
• Lupus erythematosus
• Metabolic/respiratory alkalosis or acidosis
• Protein rich diet

Drug administration

• Acetazolamide
• Aldosteronism
• Amyloidosis
• Antibiotics
• Sodium acetate
• Sodium bicarbonate
• Sodium lactate

Hematuria

• Microscopic hematuria
• Gross hematuria

Pyuria

• Microscopic pyuria
• Gross pyuria

Proteinuria

• Albuminuria
  • Microalbuminuria
  • Macroalbuminuria
• Paraproteinuria

Cells

• Benign
• Malignant

Casts and Crystals

Casts

Acellular casts

• Hyaline casts
• Granular casts
• Waxy casts
• Fatty casts
• Pigment casts
• Crystal casts

Cellular casts

• RBC casts
• WBC casts
• Bacterial casts
• Epithelial cell casts

Crystals

• Struvite crystals (magnesium-ammonium-phosphate)
• Bilirubin crystals
• Calcium carbonate crystals
• Amorphous crystals
• Calcium oxalate dihydrate crystals
• Cystine crystals

Other

• Urinary beta-HCG (urinary pregnancy test)
• Myoglobinuria
• Glucosuria
• Ketonuria
• Catecholamines
• Bacterial antigens
• Sperm
• Urinary drug concentration
• Dissolved heavy metals (e.g. copper, zinc, chromium, lead, cadmium)

Urine Culture

Normal urine is sterile. Presence of microorganisms in urine may be associated with urinary infections.

• Fungi
• Bacteria

Urine Quantity (Volume)

• The amount of urine produced depends on hydration (volume of fluid intake), physical activity, environmental factors, body surface area, and general health condition.
• In adult humans, the average urine production is approximately 1 L to 2 L per 24 hours.

High Output

• Polyuria: Excessive urinary production > 2.5 L per 24 hours

Low Output

• Oliguria: Urine production < 400 mL / 24 hours
• Anuria: Urine production < 100 mL / 24 hours

References

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