PHYSICAL EXAMINATION
OF URINE
CHAPTER 4
Copyright © 2014. F.A. Davis Company
Learning Objectives
Upon completing this chapter, the reader will be able to
1. List the common terminology used to report normal urine
color.
2. Discuss the relationship of urochrome to normal urine color.
3. State how the presence of bilirubin, biliverdin, uroerythrin,
and urobilin in a specimen may be suspected.
4. Discuss the significance of cloudy, red urine and clear, red
urine.
5. Name two pathologic causes of black or brown urine.
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Learning Objectives (cont’d)
6.
7.
8.
9.
Discuss the significance of phenazopyridine in a specimen.
State the clinical significance of urine clarity.
List the common terminology used to report clarity.
Describe the appearance and discuss the significance of
amorphous phosphates and amorphous urates in freshly
voided urine.
10. List three pathologic and four nonpathologic causes of cloudy
urine.
11. Define specific gravity, and tell why this measurement can be
significant in the routine analysis.
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Learning Objectives (cont’d)
12. Describe the principles of the refractometer, reagent strip, and
osmolality for determining specific gravity.
13. Given the concentration of glucose and protein in a specimen,
calculate the correction needed to compensate for these highmolecular-weight substances in the refractometer specific
gravity reading.
14. Name two nonpathogenic causes of abnormally high specific
gravity readings using a refractometer.
15. Describe the advantages of measuring specific gravity using a
reagent strip and osmolality.
16. State possible causes of abnormal urine odor.
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Introduction
• Physical examination of urine includes
– Color
– Clarity
– Specific gravity
• Results provide
– Preliminary information
– Correlation with other chemical and microscopic
results
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Physical Characteristics
• Provides preliminary information concerning
disorders such as
– Glomerular bleeding
– Liver disease
– Inborn errors of metabolism
– Urinary tract infection
– Renal tubular function
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Color
• Ranges from colorless to black
• Normal variations caused by
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Normal metabolic functions
Physical activity
Ingested materials
Pathologic conditions
• Abnormal variations caused by
– Bleeding
– Liver disease
– Infection
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Normal Urine Color
• Common terminology
– Pale yellow, yellow, dark yellow
– Should be consistent within institution
– Urochrome is pigment causing yellow color
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Normally excreted at a constant rate
Increased in thyroid disorders and fasting
Increases when specimen sits at room temperature
Provides estimate of body hydration
Pale yellow to dark yellow can be normal
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Normal Urine Color (cont’d)
• Additional pigments uroerythrin, urobilin
– Color changes in older specimens
• Uroerythrin
– Pink pigment
– Attaches to amorphous urates formed in refrigerated
specimens
• Urobilin
– Oxidation of normal constituent, urobilinogen
– Orange-brown color in older specimens
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Abnormal Urine Color
• Many colors and causes
• Often reason patient comes to the physician
• Common abnormal colors
– Dark yellow/amber/orange
– Red/pink/brown
– Brown/black
– Blue/green
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Dark Yellow/Amber/Orange
• Dark yellow and amber
– Normal = concentrated urine
– Abnormal = bilirubin
• Bilirubin indicates possible hepatitis virus present
– Standard precautions
• Foam
– Bilirubin produces yellow foam when shaken
– Normal urine produces small amount of white foam
caused by protein
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Dark Yellow/Amber/Orange (cont’d)
• Photooxidation of large amounts of urobilinogen
produces yellow-orange urine
– No yellow foam when shaken
• Photooxidation of bilirubin to biliverdin produces
yellow-green urine
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Dark Yellow/Amber/Orange (cont’d)
• Phenazopyridine (pyridium) or Azo-Gantrisin for
urinary tract infection produces thick orange
pigment and yellow foam (no bilirubin)
– Thick pigment is noticeable, obscures natural color,
and interferes with reagent strips
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Red/Pink/Brown
• Blood is a common cause of red urine
– Color can range from pink to brown
– Pink = small amount of blood
– Brown = oxidation of hemoglobin to methemoglobin
• Methemoglobin
– RBCs remaining in acid urine
– Fresh brown specimen can indicate glomerular bleeding
• Cloudy red urine = RBCs
• Clear red urine = hemoglobin/myoglobin
• Hemoglobin
– In vivo lysis of RBCs
– Patient’s plasma will also be red
– Consider in vitro lysis/specimen handling
Copyright © 2014. F.A. Davis Company
Red/Pink/Brown (cont’d)
• Myoglobin
– Breakdown of skeletal muscle
– Fresh urine is often more reddish/brown
– Patient’s plasma is clear
• Port wine–colored urine
– Oxidation of porphobilinogen to porphyrias
• Nonpathogenic red urine
– Menstrual contamination
– Pigmented foods
– Medications (rifampin, pheno-compounds)
• Fresh beets
– Genetically susceptible people in alkaline urine
• Black raspberries in acid urine
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Brown/Black
• Additional testing for specimens that
– Turn black after standing at room temperature
– Test negative for blood
• Melanin
– Excess in malignant melanoma
– Oxidation of melanogen to melanin
• Homogentisic acid
– Black color in alkaline urine
– Alkaptonuria
• Medications, levodopa, phenol derivatives, flagyl
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Blue/Green
• Urinary and intestinal bacterial infections are the
pathogenic cause
– Urinary: pseudomonas infection
– Intestinal: infection causing increased urinary indican
oxidizing to indigo blue
• Catheter bags: purple color from Klebsiella,
Providencia, and indican
• IV phenol medications cause green
– Clorets (green) medications: Robaxin, methylene blue,
Elavil (blue)
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Color and Clarity Procedure
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Use a well-mixed specimen
View through a clear container
View against a white background
Maintain adequate room lighting
Evaluate a consistent volume of specimen
Determine color and clarity
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Clarity
• Refers to the transparency or turbidity of a specimen
• Normal reporting
– Clear, hazy, cloudy, turbid, milky
• Visual examination
– Gently swirl specimen in a clear container in front of a
good light source
• Automated turbidity readings are available
• Fresh clean-catch urine is normally clear
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Urine Clarity
• Clear:
• Hazy:
No visible particulates, transparent
Few particulates, print easily seen
through urine
• Cloudy: Many particulates, print blurred
through urine
• Turbid: Print cannot be seen through urine
• Milky: May precipitate or be clotted
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Nonpathogenic Turbidity
• Hazy female specimens with squamous epithelial
cells and mucus
• Bacterial growth in nonpreserved specimens
• Refrigerated specimens with precipitated
amorphous phosphates (white) and urates (pink)
• Contamination: fecal, talc, semen, vaginal
creams, IV contrast media
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Pathologic Turbidity
• Most common: RBCs, WBCs, bacteria
• Also: nonsquamous epithelial cells, yeast, abnormal
crystals, lymph fluid, lipids
• The extent of turbidity should correspond to the
amount of material observed in the microscopic
examination
• Clarity is one of the criteria considered in
determining the necessity of performing a
microscopic examination
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Specific Gravity (SG)
• Evaluation of urine concentration
• Determines if specimen is concentrated enough
to provide reliable screening results
• Definition: the density of a solution compared
with the density of an equal volume of distilled
water at the same temperature
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Specific Gravity (SG) (cont’d)
• Isosthenuric: SG of 1.010 (the SG of the plasma
ultrafiltrate)
• Hyposthenuric: SG lower than 1.010
• Hypersthenuric: SG higher than 1.010
• Normal random specimen range
– 1.003 to 1.035; most common 1.015 to 1.025
– Below 1.003 may not be urine
• Consistent low readings: further testing
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Refractometer
• Measures velocity of light in air versus velocity of
light in a solution
• Concentration changes the velocity and angle at
which the light passes through the solution
• Prism in the refractometer determines the angle
that light is passing through the urine and
converts angle to calibrated viewing scale
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Refractometer (cont'd)
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Refractometer (cont’d)
• Advantages
– Temperature compensation not needed
• Light passes through temperature-compensating liquid
• Compensated between 15°C and 38°C
– Small specimen size: one or two drops
Copyright © 2014. F.A. Davis Company
Glucose and Protein Corrections
• Subtract 0.003 for each gram of protein present
• Subtract 0.004 for each gram of glucose present
• Protein or glucose concentration can be
determined from the chemical reagent strip tests
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Correction Example
• A specimen containing 1 g/dL protein and 1 g/dL
glucose has a specific gravity reading of 1.030
• Calculate the corrected reading
1.030 – 0.003 (protein) = 1.027 – 0.004 (glucose) =
1.023 corrected specific gravity
Copyright © 2014. F.A. Davis Company
Methodology
• Drop of urine placed on prism
• Focus on light source, and read
scale
• Wipe off prism between
specimens
• Calibration
– Distilled water should read 1.000;
adjust set screw if necessary
– 5% NaCl should read 1.022 ± 0.001
– 9% sucrose should read 1.034 ±
0.001
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Clinical Correlations
• Abnormally high results = >1.040
– Radiographic contrast media (IVP)
– Dextran, other IV plasma expanders
– Check patient’s clinical course/history
• Reagent strip readings and osmometry not
affected by high-molecular-weight substances
– Should be used as an alternative if possible
Copyright © 2014. F.A. Davis Company
Copyright © 2014. F.A. Davis Company
Osmolality
• A more representative measure of renal concentrating
ability can be obtained
• Specific gravity depends on the number of particles
present in a solution and the density of these particles
• Osmolality is affected only by the number of particles
present
– Substances of interest are small molecules
• Sodium
• Chloride
• Urea
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Osmole
• 1 g molecular weight of a substance divided by
the number of particles into which it dissociates
(= to MW of substance)
– Glu = 180 g/osm (C + H + O)
– NaCl = 58.5 g/osm (Na + Cl)
• The unit of measure used in the clinical
laboratory is the milliosmole (mOsm)
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Osmolarity
• Osmolality of a solution can be determined by
measuring a property that is mathematically related
to the number of particles in the solution
– Colligative property
• Changes in colligative properties
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Lower freezing point
Higher boiling point
Increased osmotic pressure
Lower vapor pressure
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Measuring Osmolality
• Measuring osmolality in the urinalysis laboratory
requires an osmometer
– Additional step in the routine urinalysis procedure
• Automated osmometer utilizes freezing point
depression to measure osmolality
Copyright © 2014. F.A. Davis Company
Reagent Strip SG
• The reagent strip reaction is based on the change in pKa
(dissociation constant) of a polyelectrolyte in an alkaline
medium
– Releasing H ions in direct proportion to the number of ions in the
solution
– The more hydrogen ions released, the lower is the pH
– Indicator bromothymol-LS blue on the reagent pad measures the
change in pH
– Indicator changes from blue (1.000 [alkaline]), through shades of
green, to yellow (1.030 [acid])
– Not affected by nonionizing substances
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Specific Gravity Dip Stick
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Odor
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Not routinely reported
Fresh urine: faintly aromatic
Older urine: ammonia
Metabolic disorders: maple syrup urine disease,
ketosis (fruity), infection (ammonia/unpleasant)
• Food: garlic, onions, asparagus (genetic: only
certain people can smell asparagus, but all
produce odor)
Copyright © 2014. F.A. Davis Company
Common Causes of Urine Odor
Odor
Aromatic
Foul,
ammonia-like
Fruity, sweet
Maple syrup
Mousy
Rancid
Sweaty feet
Cabbage
Bleach
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Cause
Normal
Bacterial decomposition, urinary tract
infection
Ketones (diabetes mellitus, starvation,
vomiting)
Maple syrup urine disease
Phenylketonuria
Tyrosinemia
Isovaleric acidemia
Methionine malabsorption
Contamination