Routine urinalysis examines the physical properties of urine such as clarity, color, odor, and specific gravity. Variations in these physical characteristics may be indicative of renal or metabolic disorders. However, many things can impact the urine's physical characteristics, such as diet and the manner in which the specimen is handled and stored. In order to assure accuracy, the sample should be analyzed immediately. Urine samples that cannot be analyzed within one hour of collection must be refrigerated.
Urine clarity, also called transparency, can indicate the presence of disease. Fresh urine is normally clear or slightly cloudy immediately after voiding. The terminology used to describe the clarity of urine includes clear, hazy, cloudy, turbid, or opalescent (milky). Each clinical laboratory has a standard system of nomenclature for describing the clarity of urine.
Alterations in the clarity of urine may occur in a variety of ways. Urine can become cloudy if it sits at room temperature or is refrigerated. However, cloudiness in a fresh urine specimen is usually indicative of an abnormal condition. Elements that alter urine clarity and may be associated with disease are blood cells, renal epithelial cells, mucus, casts, abnormal crystals, amorphous urates, and bacteria, yeast, fungus, or parasites.
Normally urine is yellow in color, but the concentration of urine affects its color. Highly concentrated urine is a darker yellow or amber and diluted urine is a lighter yellow. The color of urine may be affected by diet, hydration, medications, and disease. Urine colors are useful in providing clues that may lead to the diagnosis of abnormal conditions. Table 6-1 presents the variations in urine color and possible causes.
Fresh urine has a characteristic aromatic odor. Diet, drugs, disease, and microorganisms may alter the odor of urine and alert the practitioner to potential problems or abnormalities. Although odor itself is not diagnostic, the presence of specific types of odors may be associated with certain diagnoses.
The urine of an uncontrolled diabetic may have a fruity odor because of the presence of ketones. Infants with phenylketonuria (PKU), a metabolic disorder involving the amino acid phenylalanine, have a mousy or musty odor to their urine. Maple syrup urine disease, a metabolic disorder that can be diagnosed in infants, is characterized by urine that smells like maple syrup. Urine containing bacteria may present an ammonia odor, particularly if the urine is left unrefrigerated. A fresh urine specimen that has a foul order usually indicates a urinary tract infection.
Table 6-1. Urine Colors and Their Causes
Color Caused by Food or Medication
Yellow-orange Green, blue-green Brown-black
Beets, rhubarb (in alkaline urine) Carrots, some antibiotics Drugs such as amitriptyline, Clorets Methyldopa, metronidazole
Color Caused by Disease States
Yellow-brown or green-brown, foamy when shaken
Pale to pale greenish
Pale, foamy when shaken Dark yellow, brown-red
Red blood cells, hemoglobin, myoglobin
Melanin, homogentisic acid, hemoglobin or myoglobin (in acid urine)
Diabetes insipidus, Diabetes mellitus
The specific gravity of urine is the ratio of the weight of a given volume of urine to the weight of an equal volume of water at a given temperature. Specific gravity provides information about the ability of the kidney to reabsorb water and essential chemicals before they are excreted in the urine. Urinary specific gravity is an indication of the concentration of substances dissolved in urine. These substances can include phosphates, chlorides, urea, proteins, and sugars. Specific gravity may be measured using a uri-nometer, a refractometer, or a reagent strip.
Clear, not cloudy Yellow, straw to amber Characteristic aromatic odor 1.005-1.035
Variations from Normal. Abnormalities in the physical characteristics of urine may indicate renal or metabolic disease, infections, or obstructions.
Interfering Circumstances. Food, fluids, and medications can alter the physical characteristics of urine. Improper storage and handling of the urine sample may negatively affect the physical analysis of urine.
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