lab medicine conference : urinalysis jim holliman, m.d., f.a.c.e.p. professor of surgery and...
TRANSCRIPT
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Lab Medicine Conference :
Urinalysis
Jim Holliman, M.D., F.A.C.E.P.Professor of Surgery and Emergency MedicineDirector, Center for International Emergency MedicineM. S. Hershey Medical CenterPenn State UniversityHershey, Pennsylvania, U.S.A.
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Indications for Urinalysis
ƒ Suspect / confirm UTIƒ R/O primary renal diseaseƒ R/O systemic disease with major
renal manifestationƒ Assess complications of
hypertensionƒ Assess presence or amount of
endogenous or exogenous excreted substances
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Complete Urinalysis : Componentsƒ Color / appearanceƒ Specific gravityƒ pHƒ Chemistries
–protein–glucose–ketones–bilirubin / urobilinogen–hemoglobin / blood–nitrite–leucocyte esterase
ƒ Microscopic exam–cells / casts–bacteria–other organisms–crystals
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Secondary, Optional Tests on Urine
ƒ Cultureƒ Quantitative cultureƒ Sensitivityƒ Gram stainƒ Acid-fast stainƒ Protein electrophoresisƒ Antigen detection
(immunofluorescence)ƒ Quantitative assays
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What is Urine, Anyway ?
ƒ 95 % water, 5 % solidsƒ 3 main components :
–water –urea–NaCl
ƒ Color from pigments urochrome & urobilin
ƒ Intensity of color parallels degree of contamination
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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")
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“Minicath” urine collection tube
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Problems with Delayed Analysis of Unrefrigerated Urine
ƒ Bacteria split urea to ammonia, & urine becomes alkaline
ƒ Casts decomposeƒ Red cells lyseƒ Bacterial counts increaseƒ Glucose decreases
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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
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Causes of Increased Turbidity of Urine
ƒ Urate crystals in acid urineƒ Phosphates in alkaline urineƒ RBC'sƒ WBC'sƒ Bacteriaƒ Vaginal secretionsƒ Fat globules
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Differential diagnosis of red-orange urine color
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Differential diagnosis of red or pink urine color
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Differential diagnosis of purple urine color
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Differential diagnosis of red-brown urine color
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Differential diagnosis of brown-black urine color
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Differential diagnosis of yellow-brown urine color
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Differential diagnosis of yellow urine color
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Differential diagnosis of yellow-orange urine color
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Differential diagnosis of colorless urine
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Differential diagnosis of milky-colored urine
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Parasitic chyluria due to Wucheria bancrofti or other filaria ; can cause thoracic duct fistulas to the kidney or bladder
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Differential diagnosis of blue-green urine color
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Differential diagnosis of brown-green urine color
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Differential diagnosis of yellow-green urine color
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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 refractometerƒ 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
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Causes of Falsely High S.G. Readings
ƒ Excretion of radiopaque contrast media
ƒ Excessive proteinuria (as in nephrosis or diabetes)
ƒ Excessive glycosuriaƒ Refrigerated urine
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Diagnostic Clues from Urine pH
ƒ Range 4.6 to 8 ; normal about 6ƒ Animal protein diet : acid urineƒ Vegetable / fruit diet : alkaline urineƒ Stones that develop in alkaline urine :
–Calcium phosphate–Calcium carbonate–Mg PO4
ƒ Stones that develop in acid urine :–Uric acid–Cysteine–Calcium oxalate
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Protein Analysis in U/A'sƒ Normal urine contains small amounts of
albumin & globulinƒ 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
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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
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Correlation of Urine Glucose Readings
Reading mg/deciliter Glucose
Negative 0
Trace 100
1+ 250
2+ 1000
3+ 2000
4+ >2000
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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
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Causes of False Positive Urine Ketones
ƒ Levodopaƒ Phenolphthalein (in laxatives)ƒ Insulinƒ Pyridium (phenazopyridine)ƒ Phenforminƒ Phenylketonuria
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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 positiveƒ False negatives :
–Chlorpromazine, selenium–Exposure to light (inactivates to biliverdin)
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Analysis of Urobilinogen in U/A'sƒ Is colorlessƒ 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 positiveƒ High nitrates cause false negative (as in
red wines)
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Analysis of Hemoglobin in U/A'sƒ Not detectable by naked eye unless >
1:1000 blood in urineƒ 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
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Analysis of Nitrites in U/A's
ƒ Nitrites absent from normal urineƒ Most UTI bacteria reduce urinary nitrates to
nitrites using enzyme nitrate reductaseƒ 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
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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
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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
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Costs for U/A's at Hershey Medical Center
ƒ $17.00 for inpatientsƒ $12.00 for outpatientsƒ If microscopic U/A ordered
separately :–Add $15.00 for inpatients–Add $13.00 for outpatients
ƒ Urine culture is $32.00ƒ Urine C&S is $79.00
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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 %
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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
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White blood cells in urine
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Causes of Sterile Pyuria
ƒ Balanitis or urethritisƒ Bladder tumorsƒ Calculiƒ Exercise ƒ Feverƒ Glomerulonephritisƒ Renal tuberculosisƒ Viral infections
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Analysis of RBC's in Urineƒ 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
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Red blood cells in urine
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Gross hematuria from congenital urethral stricture
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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
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Bacterial urethritis
(should be treated with topical and oral anti-Staph antibiotics)
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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)
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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
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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
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Hyaline casts from protein gel in the renal tubule ; normal sediment has one to two per high power field
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Granular casts
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Red blood cell casts
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White blood cell cast
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Red cell casts in acute glomerulonephritis
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Waxy granular and cellular casts in chronic glomerulonephritis
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Hyaline cast with epithelial cells in tubulo-interstitial disease
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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)
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Crystals found chiefly in alkaline urine
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Sulfonamide crystals
Crystals found chiefly in acid urine
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Ammonio-magnesium-phosphate (struvite) crystal due to chronic U.T.I. with Proteus (alkaline urine)
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Uric acid crystals under bright field microscopy
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Uric acid crystals under polarized light
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Tyrosine crystals under bright field microscopy
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Leucine crystals under bright field microscopy
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Cystine crystals under bright field microscopy
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Uric acid crystals in a 3 month old patient evaluated for orange diaper stains ; this situation calls for evaluation of renal function tests
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Miscellaneous Agents Detectable on U/A Micro Exam
ƒ Spermatozoaƒ Trichomonadsƒ Candida albicansƒ Rarely Giardia or Entamoeba
histolyticaƒ Other parasites
–Schistosoma–Nematodes
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Trichomonas vaginalis in urine
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Candida albicans in urine
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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)
–Chlorideƒ Determine if metabolic alkalosis is chloride resistant or sensitive
–Potassiumƒ Determine site of K+ loss in hypokalemia (if < 10 meq/liter, implies GI tract as source)
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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
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Suggested Criteria for Obtaining Urine Cultures if UTI Suspected
ƒ All children (age < 14)ƒ All malesƒ 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
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Lab Medicine Conference : UrinalysisSummary
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