Lab Medicine Conference :
Urinalysis
Jim Holliman, M.D., F.A.C.E.P.
Professor of Surgery and Emergency Medicine
Director, Center for International Emergency Medicine
M. S. Hershey Medical Center
Penn State University
Hershey, Pennsylvania, U.S.A.
Indications for Urinalysis
ƒ Suspect / confirm UTI
ƒ R/O primary renal disease
ƒ R/O systemic disease with major renal
manifestation
ƒ Assess complications of hypertension
ƒ Assess presence or amount of
endogenous or exogenous excreted
substances
Complete Urinalysis : Components
ƒ Color / appearance
ƒ Specific gravity
ƒ pH
ƒ Chemistries
–protein
–glucose
–ketones
–bilirubin / urobilinogen
–hemoglobin / blood
–nitrite
–leucocyte esterase
ƒ Microscopic exam
–cells / casts
–bacteria
–other organisms
–crystals
Secondary, Optional Tests on Urine
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Culture
Quantitative culture
Sensitivity
Gram stain
Acid-fast stain
Protein electrophoresis
Antigen detection
(immunofluorescence)
ƒ Quantitative assays
What is Urine, Anyway ?
ƒ 95 % water, 5 % solids
ƒ 3 main components :
–water
–urea
–NaCl
ƒ Color from pigments urochrome & urobilin
ƒ Intensity of color parallels degree of
contamination
Urinalysis : Important Aspects
of Collection
ƒ "Clean - voided" specimen necessary if micro
exam to be done
–Cleansing of urethral meatus
–Preinsert tampon if discharge present
–Hold labia minora apart
–Midstream specimen
ƒ "Mini-cath" is option to reliably avoid menstrual or vaginal
discharge contamination
ƒ Adhesive perineal bag vs. direct bladder puncture with 22 g.
needle are collection options for peds patients (or try "Perez
reflex")
“Minicath” urine collection tube
Problems with Delayed Analysis of
Unrefrigerated Urine
ƒ Bacteria split urea to ammonia, &
urine becomes alkaline
ƒ Casts decompose
ƒ Red cells lyse
ƒ Bacterial counts increase
ƒ Glucose decreases
Diagnostic Clues from Urine Odor
ƒ Volatile acids responsible for normal urine
odor
ƒ Specific odors & dx's :
–Acetone : DKA
–Ammonia : infection with urea breakdown
–Maple Syrup Urine Disease
–Asparagus or garlic ingestion
Causes of Increased Turbidity of
Urine
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Urate crystals in acid urine
Phosphates in alkaline urine
RBC's
WBC's
Bacteria
Vaginal secretions
Fat globules
Differential diagnosis of red-orange urine color
Differential diagnosis of red or pink urine color
Differential diagnosis of purple urine color
Differential diagnosis of red-brown urine color
Differential diagnosis of brown-black urine color
Differential diagnosis of yellow-brown urine color
Differential diagnosis of yellow urine color
Differential diagnosis of yellow-orange urine color
Differential diagnosis of colorless urine
Differential diagnosis of milky-colored urine
Parasitic chyluria due to Wucheria bancrofti or other filaria ; can
cause thoracic duct fistulas to the kidney or bladder
Differential diagnosis of blue-green urine color
Differential diagnosis of brown-green urine color
Differential diagnosis of yellow-green urine color
Interpretation of Specific
Gravity in U/A's
ƒ S.G. is the ratio of urine density compared to a water
standard
ƒ S.G. indirectly measures renal concentrating ability
ƒ Is measured by dipstick or refractometer
ƒ S.G. values :
–Distilled water : 1.000
–Dilute urine : 1.001 to 1.010
–Concentrated urine : 1.025 to 1.030
ƒ Correlation with osmolarity :
–S.G. 1.010 = osmolarity 285 (same as serum)
–S.G. 1.025 = osmolarity > 600
Causes of Falsely High S.G.
Readings
ƒ Excretion of radiopaque contrast
media
ƒ Excessive proteinuria (as in nephrosis
or diabetes)
ƒ Excessive glycosuria
ƒ Refrigerated urine
Diagnostic Clues from Urine pH
ƒ Range 4.6 to 8 ; normal about 6
ƒ Animal protein diet : acid urine
ƒ Vegetable / fruit diet : alkaline urine
ƒ Stones that develop in alkaline urine :
–Calcium phosphate
–Calcium carbonate
–Mg PO4
ƒ Stones that develop in acid urine :
–Uric acid
–Cysteine
–Calcium oxalate
Protein Analysis in U/A's
ƒ Normal urine contains small amounts of albumin
& globulin
ƒ Proteinuria exists if > 20 mg/dl
–Incidence 6 to 9 % in asymptomatic patients
ƒ Dipstick tests use tetrabromophenol blue
indicator system (yellow to green as conc.
increases)
–React mainly with albumin
–False positive with quaternary ammonia
compounds & phenazopyridine dyes
Clinitest Use for Detection of
Glycosuria
ƒ Based on reduction of metal ions by glucose
ƒ False positive reactions due to :
–Hypochlorite or chlorine
–Other sugars (galactose, lactose, fructose,
maltose, as during pregnancy)
ƒ Enzyme - based tests (glucose oxidase) are more
specific for glucose
ƒ Can have false negative results with ascorbic
acid, tetracycline, or high uric acid
Correlation of Urine Glucose
Readings
Reading
mg/deciliter Glucose
Negative
0
Trace
100
1+
250
2+
1000
3+
2000
4+
>2000
Analysis for Ketones in U/A's
ƒ Choices are :
–Acetest (tablet)
–Test tube (Rothera)
–Dipstick
ƒ All use reaction between acetoacetic acid &
nitroprusside to make a violet dye complex
ƒ Acetone reaction is < 5 % of color change
ƒ Beta-hydroxybutyrate not detected
Causes of False Positive Urine
Ketones
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Levodopa
Phenolphthalein (in laxatives)
Insulin
Pyridium (phenazopyridine)
Phenformin
Phenylketonuria
Analysis of Bilirubin in U/A's
ƒ Conjugated bilirubin in normal urine up to 0.002
mg/dl
ƒ Dipstick uses diazonium salt reagent (buff to pink
to brown)
ƒ Positive test for urinary bilirubin with a negative
urine urobilinogen indicates biliary obstruction
ƒ Phenazopyridine causes false positive
ƒ False negatives :
–Chlorpromazine, selenium
–Exposure to light (inactivates to biliverdin)
Analysis of Urobilinogen in U/A's
ƒ Is colorless
ƒ Produced as byproduct of bacterial degradation
of conjugated bilirubin ; enterohepatic circulation
accounts for normal urinary excretion
ƒ Is increased with hemolysis or liver disease, &
decreased with biliary obstruction
ƒ Phenazopyridine causes false positive
ƒ High nitrates cause false negative (as in red
wines)
Analysis of Hemoglobin in U/A's
ƒ Not detectable by naked eye unless > 1:1000
blood in urine
ƒ Uses peroxidase characteristic of hemoglobin
or myoglobin to change color of chromogen
ƒ Dipsticks detect both free Hgb & myoglobin,
and intact RBC's
ƒ False positives from bromides, copper,
iodides, oxidizing agents
ƒ False negative from ascorbic acid
Analysis of Nitrites in U/A's
ƒ Nitrites absent from normal urine
ƒ Most UTI bacteria reduce urinary nitrates to nitrites using
enzyme nitrate reductase
ƒ Dipstick uses aromatic amine & diazonium compound to
produce pink color in presence of nitrite
ƒ False positive rare ( can be due to phenazopyridine)
ƒ False negatives :
–Bacterial inhibition with antibiotics
–High urine flow (dilutional) ; Frequent or continuous (foley)
voiding
–Ascorbic acid
Analysis of Leucocyte Esterase in
U/A's
ƒ Any purple color on dipstick indicates
> 5 WBC's/hpf
ƒ Detects intact & lysed WBC's & WBC
casts
ƒ False negatives :
–Cephalexin, gentamicin, nitrofurantoin
ƒ Up to 97 % sensitivity & 90 %
specificity for culture - proven UTI's
Use of "Reflex Urinalysis" at
Hershey Medical Center
ƒ "Reflex U/A" = dipstick (Chem 9)
–Micro exam done at no extra charge if dip
is positive for protein, Hgb, or leucocyte
esterase
ƒ Is indicated for routine U/A's as part of
routine physical exam, and in other
patients without possible urologic sx
Costs for U/A's at Hershey
Medical Center
ƒ $17.00 for inpatients
ƒ $12.00 for outpatients
ƒ If microscopic U/A ordered separately
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–Add $15.00 for inpatients
–Add $13.00 for outpatients
ƒ Urine culture is $32.00
ƒ Urine C&S is $79.00
Rationale for Use of Dipstick as
Screening for Micro Exam of Urine
ƒ 5 combined studies : 3205 patients
–Sensitivity : 94 %
–Specificity : 72 %
ƒ HMC study : 50 patients
–Sensitivity : 93 %
–Specificity : 72 %
ƒ Post - test probability of abnormal urine
sediment if reflex U/A is negative is 1 to 6
%
Analysis of WBC's in Urine
ƒ Normal WBC excretion in urine :
–Up to 400,000 cells per hour
–Averages 650,000 per day
–10 WBC per ml. correlates with 1 WBC per hpf
ƒ Counts exceeding 10 WBC per ml. correlate
with significant bactiuria in 40 to 84 %
ƒ Can have false negative if patient is
leucopenic
White blood cells in urine
Causes of Sterile Pyuria
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Balanitis or urethritis
Bladder tumors
Calculi
Exercise
Fever
Glomerulonephritis
Renal tuberculosis
Viral infections
Analysis of RBC's in Urine
ƒ Normal RBC excretion in urine :
–Up to 1,000,000 per day
–Average 130,000 per day
–So average is 1 RBC per 2 to 3 hpf or 500 to 1000 RBC
per ml.
ƒ Hematuria then represents greater amounts of
blood than these
ƒ For urine to be considered free of blood, both
supernatant & sediment should be dipstick
tested
Red blood cells in urine
Gross hematuria from congenital urethral stricture
Analysis for Bacteria in U/A's
ƒ Bacteria are absent in normal bladder urine
ƒ Micturition commonly deposits bacteria in urine
ƒ Classic infection definition : > 100,000 organisms
per ml. of freshly centrifuged, freshly voided
urine
ƒ Correlations with infection :
–Detection of any bacteria on uncentrifuged
specimen
– > 10 bacteria / hpf of centrifuged sample
Bacterial urethritis
(should be treated with topical and oral anti-Staph antibiotics)
Bacterial Counts in Urine
ƒ < 1000 colonies per ml. implies only
contamination
ƒ Counts > 1000 and < 100,000 per ml. may imply
infection
ƒ Counts > 100,000 / ml. almost always imply
infection
ƒ Causes of false low counts :
–pH < 5, S.G. < 1.003, voiding < 45 minutes from sample
collection, urethral obstruction, infections with fastidious
organisms, contaminants with string oxidants (bleach)
Diagnostic Significance of
Cellular Casts
ƒ Represents contents of renal tubules discharged into
urine
ƒ Cast width descriptions :
–Narrow : 1 to 2 RBC's in width
–Medium : 3 to 4 RBC's in width
–Broad : > 5 RBC's in width ; these are formed in the
collecting tubules & suggest severe renal disease
ƒ Cast types & associated diseases :
–Broad, epithelial, fatty, granular, or waxy :
parenchymal renal disease
–RBC : acute glomerulonephritis
–WBC : pyelonephritis
Diagnostic Aspects of Cellular
Casts
ƒ RBC casts
–Usually represent significant glomerular disease
–Can occur after very strenuous exercise
–Alkaline urine hemolyzes RBC's & can dissolve casts if
analysis delayed
ƒ Hyaline casts
–Clear, colorless ; due to protein precipitation
–Occurence depends on urine flow, pH, degree of
proteinuria
ƒ Granular casts
–Result from disintegration of cell material into particles
–Form waxy casts when renal failure is advanced
Hyaline casts from protein gel in the renal tubule ; normal
sediment has one to two per high power field
Granular casts
Red blood cell casts
White blood cell cast
Red cell casts in acute glomerulonephritis
Waxy granular and cellular casts in chronic glomerulonephritis
Hyaline cast with epithelial cells in tubulo-interstitial disease
Analysis for Crystals in U/A's
ƒ Crystals commonly found in normal urine
ƒ Pathologic crystals :
–Cysteine (hexagonal ; not birefingent under
polarized light, unlike uric acid)
–Leucine (yellow spheres with striations)
–Tyrosine (fine needles in rosettes)
ƒ Phosphate & urate crystals of little Dx
significance
ƒ Calcium oxalate crystals sometimes indicate
ethylene glycol poisoning (but can be normal)
Crystals found chiefly in alkaline urine
Sulfonamide crystals
Crystals found chiefly in acid urine
Ammonio-magnesium-phosphate (struvite) crystal due to
chronic U.T.I. with Proteus (alkaline urine)
Uric acid crystals under bright field microscopy
Uric acid crystals under polarized light
Tyrosine crystals under bright field microscopy
Leucine crystals under bright field microscopy
Cystine crystals under bright field microscopy
Uric acid crystals in a 3 month old patient evaluated for orange
diaper stains ; this situation calls for evaluation of renal
function tests
Miscellaneous Agents Detectable
on U/A Micro Exam
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Spermatozoa
Trichomonads
Candida albicans
Rarely Giardia or Entamoeba
histolytica
ƒ Other parasites
–Schistosoma
–Nematodes
Trichomonas vaginalis in urine
Candida albicans in urine
Measurements of Electrolytes in
Urine
ƒ Ion specific electrodes currently used (same as for
serum)
ƒ Clinical situations where measurements useful :
–Sodium
ƒ Volume depletion, acute oliguria, hyponatremia (R/O SIADH)
–Chloride
ƒ Determine if metabolic alkalosis is chloride resistant or
sensitive
–Potassium
ƒ Determine site of K+ loss in hypokalemia (if < 10 meq/liter,
implies GI tract as source)
Interpretation of Urinary Chloride
Levels in Metabolic Alkalosis
ƒ Urinary chloride 0 to 10 meq/liter ("chloride-responsive") :
–Vomiting
–NG suction
–Diuretic effect
–Post-hypercapnia
ƒ Urinary chloride > 10 meq/liter (approx. dietary intake) :
–Severe hypokalemia
–Renal failure
–Edematous states
–Mineralocorticoid excess
–Licorice ingestion
Suggested Criteria for Obtaining
Urine Cultures if UTI Suspected
ƒ All children (age < 14)
ƒ All males
ƒ Women with history of :
–Immunocompromise
–Renal abnormalities
–Diabetes mellitus
–Recent instrumentation
–Indwelling catheter
–Prolonged Sx before seeking care
–3 or more ( ? > 5 ) UTI's in last year
–Recent pyelonephritis
–Recent hospitalization
Lab Medicine Conference : Urinalysis
Summary
ƒ Assess urine color & overall
appearance
ƒ Decide if only dipstick analysis
needed
ƒ Consider explanations for each
abnormal component on dipstick &
micro
ƒ Decide if additional studies (C & S,
electrolytes, osmolality, etc.) needed