Transcript introduction to urinalysis - 36-454-f10

INTRODUCTION TO URINALYSIS
CHAPTER 2
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Learning Objectives
Upon completing this chapter, the reader will be able to
1.
2.
3.
4.
5.
6.
List three major organic and three major inorganic chemical
constituents of urine.
Describe a method for determining whether a questionable fluid is
urine.
Recognize normal and abnormal daily urine volumes.
Describe the characteristics of the recommended urine specimen
containers.
Describe the correct methodology for labeling urine specimens.
State four possible reasons why a laboratory would reject a urine
specimen.
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Learning Objectives (cont’d)
7.
List 10 changes that may take place in a urine specimen that remains
at room temperature for more than 2 hours.
8. Discuss the actions of bacteria on an unpreserved urine specimen.
9. Briefly discuss five methods for preserving urine specimens, including
their advantages and disadvantages.
10. Instruct a patient in the correct procedure for collecting the following
specimens: random, first morning, 24-h timed, catheterized,
midstream clean-catch, suprapubic aspiration, three-glass collection,
and pediatric, and identify a diagnostic use for each collection
technique.
11. Describe the type of specimen needed for optimal results when a
specific urinalysis procedure is requested.
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History
• The beginning of laboratory medicine
– Cavemen drawings and Egyptian hieroglyphics
• Color, clarity, odor, viscosity, sweetness
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Fifth century BC, Hippocrates wrote uroscopy book
AD 1140 color charts
1694 albumin determination by “boiling”
Charlatans/“pisse prophets”
• First medical licensure laws
– 17th century invention of the microscope
• Evaluation of sediment
– Part of a routine physical in 1827
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Importance
• Readily available and easily collected specimen
• Urine contains information, which can be obtained by
inexpensive laboratory tests, to assess many metabolic
functions
• CLSI Urinalysis definition: “the testing of urine with
procedures commonly performed in an expeditious,
reliable, safe, and cost-effective manner”
• Reasons to perform
– Aid disease diagnosis, screen for asymptomatic diseases,
monitor disease progress and therapy effectiveness
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Urine Formation
• Ultrafiltrate of plasma
• Kidneys converts approximately 170,000 mL of
filtered plasma
• Average daily urine output of 1200 mL
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Urine Composition
• Normal 95% water, 5% solutes
• Solute variations: diet, activity, metabolism, endocrine,
body position
• Major organic solute is urea (protein, amino acid
breakdown); makes up approximately one half of the
dissolved solids
• Inorganic chloride, sodium, and potassium
• Urea and creatinine identify a fluid as urine
• May also contain cells, casts, crystals, mucus, and bacteria
– Increases indicative of disease
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Urine Volume
• Determined by body’s state of hydration
• Influenced by fluid intake, nonrenal fluid loss,
antidiuretic hormone (ADH) variations, excretion
of large amounts of dissolved solids (e.g.,
glucose)
• Usual daily volume = 1200 to 1500 mL
• Normal range = 600 to 2000 mL
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Definitions
• Oliguria: a decrease in urine output
– <1 mL/kg/h in infants <0.5 mL/kg/h in children, <400 mL/day
in adults
– Causes: vomiting, diarrhea, perspiration, severe burns
• Anuria: cessation of urine flow
– Severe kidney damage, decreased renal blood flow
• Nocturia: increased urine excretion at night
– Normally two to three times more excretion in the day
• Polyuria: >2.5 L/day in adults and >2.5 to 3 mL/kg/day in
children
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Polyuria in Diabetes Mellitus versus Diabetes Insipidus
Diabetes mellitus
Diabetes insipidus
• Increased volume caused
by need to excrete the
excess glucose not
reabsorbed from the
ultrafiltrate
• Patients exhibit polydipsia
(Increased water intake)
• Urine appears dilute with
a high specific gravity
• Decreased production or
function of antidiuretic
hormone (ADH) causing
decreased reabsorption of
water from ultrafiltrate
• Urine is dilute with low
specific gravity
• Patients also exhibit
polydipsia
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Specimen Collection
• Wear gloves when working with urine
• Clean, dry, leak-proof containers
• Disposable, wide-mouthed, and flat-bottom containers
with screw caps are recommended
• Clear containers/at least 50 mL capacity
– Sterile transfer devices and containers are available
– Facilitates automated analysis
– 12 mL minimum for analysis
• Adhesive bags for pediatrics
• Large plastic containers for 24-hour specimens
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Specimen Labeling
• Information on label
– Patient’s name, ID number, date, time
• Additional information: age, location, health-care
provider’s name
• Place label on container, not lid
• Requisition form (manual or computerized)
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Must accompany specimen
Information must match label
Time of receipt is stamped on requisition
Other information: type of specimen, interfering medications
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Specimen Rejection
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Specimens in unlabeled containers
Nonmatching labels and requisition forms
Specimens contaminated with feces or toilet paper
Containers with contaminated exteriors
Specimens of insufficient quantity
Specimens that have been improperly transported
Labs must have written policies for rejection of
specimens
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Specimen Integrity
• Changes in urine composition take place not only
in vivo but also in vitro
– Test within 2 hours of collection
– Refrigerate or chemically preserve if testing is
delayed
– Most problems are caused by bacterial multiplication
– Increased: color, turbidity, pH, nitrite, bacteria, odor
– Decreased: glucose, ketones, bilirubin, urobilinogen,
RBCs, WBCs, casts
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Changes in Unpreserved Urine
Analyte
Change
Cause
Color
Modified/darkened
Oxidation or reduction of metabolites
Clarity
Decreased
Odor
Increased
pH
Increased
Bacterial growth and precipitation of
amorphous material
Bacterial multiplication causing breakdown of
urea to ammonia
Breakdown of urea to ammonia by ureaseproducing bacteria/loss of CO2
Glucose
Decreased
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Glycolysis and bacterial use
Changes in Unpreserved Urine (cont’d)
Analyte
Ketones
Change
Decreased
Cause
Volatilization and bacterial metabolism
Bilirubin
Decreased
Exposure to light/photooxidation to biliverdin
Urobilinogen
Decreased
Oxidation to urobilin
Nitrite
Increased
Multiplication of nitrate-reducing bacteria
RBCs, WBCs,
and casts
Decreased
Disintegration in dilute alkaline urine
Bacteria
Trichomonas
Increased
Decreased
Multiplication
Loss of motility, death
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Specimen Preservation
• Routine is refrigeration at 2°C to 8°C
– Decreases bacterial growth and metabolism
– Must return to room temperature for chemical testing
• Chemical preservative
– Ideal is bactericidal: inhibits urease and preserves formed
elements
– Should not interfere with chemical tests
• Commercial transport tubes are available, but they
must be compatible with tests
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Preservatives
Preservatives
Advantages
Refrigeration
Does not interfere Precipitates amorphous
with chemical tests phosphates and urates
Prevents bacterial growth
for 24 h2
Boric acid
Prevents bacterial
growth and
metabolism
Keeps pH at about 6.0
Can be used for urine
culture transport
Formalin
(formaldehyde)
Excellent sediment
preservative
Sodium fluoride
Disadvantages
Interferes with drug and
hormone analyses
Acts as a reducing agent,
interfering with chemical
tests for glucose, blood,
leukocyte esterase, and
copper reduction
Is a good
Inhibits reagent strip tests
preservative for drug for glucose, blood, and
analyses
leukocytes
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Additional Information
Rinse specimen container
with formalin to preserve
cells and casts
Preservatives (cont’d)
Preservatives
Advantages
Disadvantages
Commercial
Convenient when
Check tablet composition to
determine possible effects on
preservative tablets refrigeration not
possible
desired tests
Have controlled
concentration to
minimize interference
Urine Collection
Contains collection cup,
4
Kits (Becton
transfer straw, C&S
Dickinson,
preservative tube or
Rutherford, NJ)
UA tube
Additional Information
Light gray and gray
C&S tube
Preservative is boric acid,
sodium borate, and sodium
formate
Keeps pH at about 6.0
Sample stable at room Do not use if urine is below
temperature (RT) for 48 minimum fill line
h; prevents bacterial
growth and
metabolism
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Types of Specimen
• The composition of urine depends on the
patient’s metabolic state and the timing and
procedure used for collection
• Time, length, and method of collection and the
patient’s dietary and medicinal intake
• Patients must be instructed when special
collection techniques are required
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Random Specimen
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Most common type received
Routine screening for obvious abnormalities
May be collected at any time
Collection time must be recorded
Dietary intake and physical activity may alter
results
• Patients may have to collect an additional
specimen under controlled conditions
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First Morning Specimen
• Ideal screening specimen
– Patient is in a basal state
• Use for orthostatic protein confirmation and
urine pregnancy tests
• More concentrated than a random specimen
• Patient collects immediately on arising, delivers
to lab within 2 hours
– Refrigeration is an alternative
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Fasting Specimen
• Actually is second specimen voided, collected
after the first morning specimen
• Does not contain metabolites from evening meal
• Recommended for glucose monitoring
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24-Hour (Timed) Specimen
• Carefully timed specimen will produce accurate quantitative
results
• Good for diurnal variation solutes
– Catecholamines, electrolytes
• The patient must remain adequately hydrated during short
collection period
• Patient must be instructed on the procedure for collecting a
timed specimen
• Concentration of a substance in a particular period must be
calculated from the urine volume produced during that time
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24-Hour (Timed) Specimen (cont’d)
• 24-hour specimen must be thoroughly mixed and
the volume accurately measured and recorded
• Multiple containers of the same collection must
be combined and mixed thoroughly
• Additives should not interfere with the tests to
be performed
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24-Hour (Timed) Specimen (cont’d)
• Required for quantitative results
• 24-hour specimens are needed for measuring
substances with diurnal variation (results differ in
a.m. and p.m.) and substances that vary with
meals, activity, and body metabolism
• Shorter timed specimens can be used for
substances with consistent levels
• Accurate timing is critical for accurate results
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2-Hour Postprandial Specimen
• Patient voids before eating routine meal
• Eats meal
• Collects next specimen 2 hours after finishing
meal
• Monitors insulin therapy
• Results can be compared with fasting urine
specimen and blood test results
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Glucose Tolerance Specimen
• Institutional option for collection with blood
glucose tolerance test, not frequently done
• Specimens are collected at the same intervals as
the blood samples
• Used to correlate renal threshold with patient’s
ability to metabolize glucose
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Catheterized Specimens
• Sterile specimen collected from bladder with a
hollow tube (catheter)
• Most common test is bacterial culture
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Midstream Clean-Catch Specimen
• Alternative to catheterized specimen
– Less traumatic method
• Less contaminated than routine collection
• Provide patient with mild cleansing material and
container and instructions
• Do not touch or contaminate inside of container
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Suprapubic Aspiration
• Completely free of contamination for culture and
cytology
• External introduction of needle for aspiration
from the bladder
• Possible pediatric specimen
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Prostatitis Specimen
• Collection similar to midstream clean-catch
• Three-glass collection
– Container 1: first urine passed
– Container 2: midstream urine
– Massage prostate to obtain prostatic fluid
– Container 3: remaining urine and fluid
– Quantitative cultures on all three specimens, examine
1 and 3 microscopically for WBCs
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Prostatitis Specimen (cont’d)
• Prostatic infection = higher WBC/hpf count in
specimen 3 than specimen 1; bacterial count in
specimen 3 is 10 times higher than in specimen 1
• Specimen 2 is a control for bladder or kidney
infection
– Positive culture in specimen 2 invalidates positive
culture in specimen 3 (cannot differentiate urinary
tract infection from prostate infection)
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Prostatitis Specimen (cont’d)
• Pre- and postmassage test
– Specimen 1: midstream clean-catch specimen
– Specimen 2: postmassage specimen
• Prostatitis is indicated by a quantitative culture
result in the second glass that is 10 times higher
than specimen 1
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Pediatric Specimens
• Soft, clear, plastic bags, with hypoallergenic tape
applied to genital area
• Monitor bag frequently
• Clean-catch method with sterile bag can be used
– Cleaning for microbiology specimens
• Bags with tubes to a larger container are
available for timed specimens
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Drug Specimen Collection
• Proper collection, labeling, and handling must be
documented
• Chain of custody: documentation from the time
of specimen collection until the time of receipt of
laboratory results
– Free of substitution, adulteration, or dilution
• Standardized form always accompanies specimen
• Specimen must withstand legal scrutiny
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Drug Specimen Collection (cont’d)
• Points to consider
– Photo ID of urine donor or ID by employer
– No unauthorized access to specimen
• Witnessed versus unwitnessed collection
– Determined by test orderer
– Both specimens must be handed immediately to
collector
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Drug Specimen Collection (cont’d)
• Adulteration tests
– Temperature taken within 4 minutes must be 32.5°C
to 37.7°C
– Report temperatures outside of range immediately
– Collect another specimen ASAP
– Inspect urine color for anything unusual
• Follow laboratory instructions for labeling,
packaging, and transport
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