Chemical Examination of Urine - Nitrite, Bilirubin, Urobilinogen, and Secondary Testing. Flashcards
What test results indicate a patient has a UTI?
Leukocyte and nitrite positive.
Some bacteria have the ability to reduce nitrite into:
Nitrate. They have an enzyme called nitrate reductase.
The nitrite test is a rapid screening test for?
The presence of bacteria or for a UTI.
Which type of UTI is more common and what type of bacteria is the usually cause?
- Ascending infection.
- Gram negative rods.
What are the main bacteria responsible for UTI’s?
- E. coli.
- Proteus.
- Enterobacter.
- Klebsiella.
What causes a patient to have nitrates in their urine?
The presence of nitrate reductase producing bacteria. The longer the bacteria has been in the bladder, the more nitrates in the urine.
What is the principle reaction for a nitrite test?
Nitrites in an acidic pH will react with the aromatic amine forming a diazonium salt. The diazonium salt then reacts with the aromatic compound on the reagent pad, resulting in a color change from the azo dye being produced.
What is the specificity for a nitrites test?
Specific for nitrites.
What is the sensitivity of the chemstrip test for nitrites?
0.05 mg/dL.
What is the sensitivity of the multistix test for nitrites?
0.06 mg/dL.
What is the key amine reagent for nitrites on the chemstrip?
Sulfonamide
What is the key amine reagent for nitrites on the multistix?
P-arsanilic acid.
What is the key aromatic compound for nitrites?
Tetra-hydrobenzoquinolinol.
What causes a false positive nitrites test?
- Pyridium.
- Beets.
- Improper storage.
What causes a false negative nitrites test?
Ascorbic acid levels > 25mg/dL.
What is the expected result for a nitrite test?
Negative
What are the reportable results for the nitrites?
Positive or negative.
Any positive amount of bilirubin found in the urine is significant because:
- Early indicator of liver disease.
- Detectable before jaundice.
What are the 3 mechanisms of abnormal bilirubin metabolism?
- Prehepatic.
- Hepatic.
- Posthepatic.
Excess breakdown of red blood cells:
Prehepatic.
Liver can not conjugate all of the bilirubin:
Hepatic.
Conjugated bilirubin can’t make it to the intestine to become unconjugated:
Posthepatic.
For prehepatic conditions, what are the expected results for uroblilinogen and bilirubin?
- Urobilinogen: ↑↑.
- Bilirubin: negative.
For hepatic conditions, what are the expected results for uroblilinogen and bilirubin?
- Urobilinogen: Normal or ↑.
- Bilirubin: ↑.
For posthepatic conditions, what are the expected results for uroblilinogen and bilirubin?
- Urobilinogen: ↓↓.
- Bilirubin: ↑↑.
What is the principle behind the bilirubin test?
Diazonium salt reacts with bilirubin glucuronide to produce a Azo dye.
What are the key reagents for the bilirubin on a chemstrip?
Dicchlorobenzene diazonium tetrafluoroborate.
What are the key reagents for the bilirubin on a multistix?
Dichlorobenzene diazonium salt.
What can cause a false positive bilirubin test?
Pyridium
What can cause a false negative bilirubin test?
Strong reducing substance.
What is the sensitivity of the bilirubin test?
0.4 - 0.8 mg/dL.
What are the limitations of the bilirubin test?
Photo oxidation.
How is the bilirubin test reported?
- Negative.
- Positive: small (+), moderate (++), large (+++).
What does a urine sample look like if it is expected to be positive for bilirubin?
Amber with yellow foam.
What type of bilirubin is being detected by the reagent strip?
Conjugated.
What is the specimen of choice for urobilinogen is?
- Right after a meal.
- During the “alkaline tide”.
What is the principle of the urobilinogen multistix test?
Classic Ehrlich’s reaction: urobilinogen + p-dimethylaminobenzaldehyde in acid = a red color change.
What is the principle of the urobilinogen chemstrip test?
Azocoupling reaction.
What is the key reagent for the urobilinogen chemstrip test?
4- methoxybenzine-diaonium-fluoroborate.
What is the key reagent for the urobilinogen multistix test?
Ehrlich’s reagent.
What results are reportable for urobilinogen?
- Ehrlich units or mg/dL. (1 mg = 1 EU).
- 0.02, 1.0, 2.0, 4.0, >8.0.
- Normal results are 0.2 or 1 mg/dL.
What is the specificity for the urobilinogen test?
- False positives from drugs and other substances.
- Absences of urobilinogen cannot be measured.
- Chemstrip is more specific for urobilinogen.
What is the sensitivity for the urobilinogen test?
0.2 mg/dL.
What are the limitations of the urobilinogen test?
Can only be reported in increments of 0.005.
What if the confirmatory test for reducing sugars?
Clinitest
What is the confirmatory test for bilirubin?
Ictotest
What is the confirmatory test for ketones?
Acetest
What is the confirmatory test for proteins?
Sulfosalycilic acid.
What is the principle of the clinitest?
- Reducing sugars convert cupric sulfate to corpus oxide.
- Color change fro blue- green- orange.
What is the “pass through phenomenon”?
The test isn’t read at the exact time, the color would change fro blue- orange- green- back to blue.
What were the uses of the clinitest?
Used for children under 2 with genetic disorders involving reducing sugars (galactosemia).
What is the procedure of the acetest (nitroprusside tablet test)?
Drop specimen on tablet and a purple color indicates a positive test.
- Ignore other colors.
