Chemical Examination of Urine

Part III:Ketones, Blood, Bilirubin &

Urobilinogen

Ricki Otten MT(ASCP)SC

uotten@unmc.edu

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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