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Chemical Examination of Urine
Part III:Ketones, Blood, Bilirubin &
Urobilinogen
Ricki Otten MT(ASCP)SC
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Ketones: Purpose
• Ketones are intermediary products of fat metabolism
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Ketones
• Three ketone bodies– Acetone 2%– Acetoacetic acid 20%– Beta-hydroxybutyric acid 78%
• Characteristic ‘fruity breath’ ~ acetone
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Ketones: Normal
• Normal: negative
• Abnormal:– Inability to utilize carbohydrates– Excessive loss of carbohydrates– Inadequate intake of carbohydrates
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Ketones: Methods
• Reagent strip
• Acetest: tablet test
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Ketones: Method
• Glycine: also measures acetone– Reagent strip: check package insert– Acetest tablets: contain glycine
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Ketones• Reagent strip
– Sensitivity: 5-10 mg/dl– Specificity: acetoacetic acid and/or acetone
• False positive: highly pigmented urine• False negative: improper specimen handling
• Acetest– Specificity: acetoacetic acid and acetone
• False positive: highly pigmented urien• False negative: improper specimen handling
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Blood: Purpose
• Blood in urine indicates pathology
• Two forms found in urine– Intact RBC– Hemolyzed RBC
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Blood: Terms
• Hematuria
• Hemoglobinuria
• Myoglobinuria
All will give a positive blood reaction
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Blood: Reagent strip
• Test can detect hemolyzed RBC
• Heme moiety imparts peroxidase activity and catalyzes the reaction
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Blood
• Sensitivity
• Specificity– Intact RBC– Hemolyzed RBC (hemoglobin)– Myoglobin
– False positives: myoglobin, oxidizing agents– False negatives: ascorbic acid
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Blood:
• Correlate reagent strip results– Microscopic findings– Color and clarity
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Bilirubin and Urobilinogen
• Bilirubin in urine is always pathologic:
liver disease
• Urobilinogen in urine: normal to have a small amount:
0.2 – 1.0 mg/dl
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Three mechanisms
• Pre-hepatic: liver is healthy
• Hepatic: liver disease
• Post-hepatic: liver is healthy, obstruction indicated
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Bilirubin: Methods
• Reagent strip
• Ictotest: tablet test
• Foam test
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Bilirubin: Methods
• Reagent strip
• Ictotest: tablet test
• Same reaction
• Same specificity: conjugated bilirubin– False positive: urine color– False negative: low concentration, ascorbic
acid, improper specimen handling
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Bilirubin: Methods
• Reagent strip
• Ictotest: tablet test
• Sensitivity differs
Reagent strip: ~0.5 mg/dl
Ictotest: 0.05 – 0.1 mg/dl
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Bilirubin: Methods
• Possible to have a negative reagent strip test and positive ictotest– Difference in sensitivity levels
• Always perform Ictotest when– Urine bilirubin test specifically ordered– Urine appearance is amber: even if bilirubin
reagent strip test is negative– Positive reagent strip test
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Bilirubin: Foam Test
• Shake urine and observe resulting foam
• Yellow foam = bilirubin
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Urobilinogen: Methods
• Reagent strip test– Two reactions dependent upon manufacturer
• Para-dimethylaminobenzaldehyde• Diazonium salt
– Cannot determine absence of UBG
• Watson-Schwartz assay
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Urobilinogen: Methods• Para-dimethylaminobenzaldehyde
– Sensitivity: 0.2 mg/dl– Specificity:
• False positive: any ‘Ehrlich reactive compound’; color masking; urine at body temp
• False negative: improper specimen handling
• Diazonium salt– Sensitivity: 0.4 mg/dl– Specificity: reacts only with UBG
• False positive: color masking• False negative: improper specimen handling
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Urobilinogen: Watson Schwartz
• Classic method used to differentiate
urobilinogen from porphobilinogen using a
differential extraction method
• Para-dimethylaminobenzaldehyde