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Clinical urine tests

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MeSH
  
D016482

MedlinePlus
  
003579

Clinical urine tests

Other codes
  
LOINC Codes for Urinalysis panels

Clinical urine tests are various tests of urine for diagnostic purposes. The most common is a urinalysis (UA), one of the most common methods of medical diagnosis. The word is a portmanteau of the words urine and analysis. Other tests are urine culture (a microbiological culture of urine) and urine electrolyte levels.

Contents

The target parameters that can be measured or quantified in urinalysis include naked-eye (gross) examination for color and smell plus analysis for many substances and cells, as well as other properties, such as specific gravity.

A part of a urinalysis can be performed by using urine test strips, in which the test results can be read as color changes. Another method is light microscopy of urine samples.

Target parameters

Urine test results should always be interpreted using the reference range provided by the laboratory that performed the test, or using information provided by the test strip/device manufacturer.

In addition to the substances mentioned in tables below, other tests include a description of color and appearance.

Color

The following are examples of color change causes and not a complete listing.

  • Nearly colorless: Excessive fluid intake for conditions; untreated diabetes mellitus, diabetes insipidus, and certain types of nephritis.
  • Yellow: Distinctly yellow urine may indicate excessive riboflavin (vitamin B2) intake.
  • Yellow-amber: Normal.
  • Yellow-cloudy: excessive crystals (crystalluria) and/or excessive pus (pyuria).
  • Orange: Insufficient fluid intake for conditions; intake of orange substances; intake of phenazopyridine for urinary symptoms.
  • Red: Leakage of red blood cells or of hemoglobin from such cells; intake of red substances.
  • Dark:
  • Reddish-orange: Intake of certain medications or other substances.
  • Rusty-yellow to reddish-brown: Intake of certain medications or other substances.
  • Dark brown: Intake of certain medications or other substances; damaged muscle (myoglobinuria) from extreme exercise or other widespread damage; altered blood; intake of phenolic substances; inadequate porphyrin metabolism; melanin from melanocytic tumors.
  • Brown black to black: Intake of substances or medications; altered blood; a problem with homogentisic acid metabolism (alkaptonuria), which can also cause dark whites of the eyes and dark-colored internal organs and tissues (ochronosis); Lysol (a product that contains phenols) poisoning; melanin from melanocytic tumors); paraphenylenediamine is a highly toxic ingredient of hair dye formulations that can cause acute kidney injury and result in black urine.
  • Magenta to purple-red: Presence of phenolphthalein, a stimulant laxative previously found in Ex-Lax.
  • Green, or dark with a greenish hue: Jaundice (bilirubinuria); problem with bile metabolism. Recent surgery requiring high doses of propofol infusion. The use of a medication (Uribel) that is similar to phenazopyridine for the relief of urinary symptoms.
  • Other colors: Various substances ingested in food or drink, particularly up to 48 hours prior to the presence of colored urine.

    • Smell

    The odor (scent) of urine can normally vary from odorless (when very light colored and dilute) to a much stronger odor when the person is dehydrated and the urine is concentrated. Brief changes in odor are usually merely interesting and not medically significant. (Example: the abnormal smell many people can detect after eating asparagus.) The urine of diabetics experiencing ketoacidosis (urine contains high levels of ketone bodies) also may also have an abnormal odor.

    Ions and trace metals

    A sodium-related parameter is fractional sodium excretion, which is the percentage of the sodium filtered by the kidney which is excreted in the urine. It is a useful parameter in acute renal failure and oliguria, with a value below 1% indicating a prerenal disease and a value above 3% indicating acute tubular necrosis or other kidney damage.

    Drugs

    Urine may be tested to determine whether an individual has engaged in recreational drug use. In this case, the urinalysis would be designed to detect whatever marker indicates drug use.

    History

    Helen Murray Free and her husband, Alfred Free, pioneered dry reagent urinalysis, resulting in the 1956 development of Clinistix (also known as Clinistrip), the first dip-and-read test for glucose in urine for patients with diabetes. This breakthrough led to additional dip-and-read tests for proteins and other substances. The invention was named a National Historic Chemical Landmark by the American Chemical Society in May 2010.

    Methods

    When doctors order a urinalysis, they will request either a routine urinalysis or a routine and microscopy (R&M) urinalysis, with the difference being a routine urinalysis does not include microscopy or culture.

    Urine test strip

    A urine test strip can quantify:

  • Leukocytes – with presence in urine known as leukocyturia
  • Nitrite – with presence in urine known as nitrituria
  • Protein – with presence in urine known as proteinuria, albuminuria, or microalbuminuria
  • Blood – with presence in urine known as hematuria
  • specific gravity

    • Microscopic examination

    The numbers and types of cells and/or material such as urinary casts can yield a great detail of information and may suggest a specific diagnosis.

  • 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, or malignant hypertension
  • White blood cell casts – associated with acute interstitial nephritis, exudative glomerulonephritis, or 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
  • Waxy casts – associated with chronic renal disease

    • Other methods

  • Urine culture – a microbiological culture of urine samples, detecting bacteriuria, is indicated when a urinary tract infection is suspected.
  • Ictotest – this test is used to detect the destruction of old red blood cells in the urine.
  • Hemoglobin test – this tests for hemolysis in the blood vessels, a rupture in the capillaries of the glomerulus, or hemorrhage in the urinary system, which cause hemoglobin to appear in the urine.

    • References

    Clinical urine tests Wikipedia
    (Text) CC BY-SA


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