Questions and Answers
What is the recommended storage condition for reagent strips?
Below 30°C in an opaque, tightly closed container with desiccant.
The reagent strip should be dipped into a well-mixed uncentrifuged urine specimen for no longer than ______ seconds.
1
What can cause a false positive for glucose in urine tests?
A tan or pink to violet color indicates a positive result for bilirubin.
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What is the positive color change for ketones in a urine test?
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What is the principle used to measure specific gravity in urine testing?
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Match the following urine tests with their positive color indicators:
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High concentrations of protein can lead to a false positive in the specific gravity test.
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What is the color indicator for the protein test?
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What is the principle of the pH test in urine examination?
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Which reagent is used for the Urobilinogen test?
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Study Notes
Reagent Strip Specifications
- Dimensions: Approximately 11-12 cm long and 4-6 mm wide, equipped with an absorbent pad.
Care of Reagent Strips
- Store in an opaque, tightly closed container with desiccant.
- Recommended storage temperature is below 30°C; freezing is not permitted.
- Avoid exposure to volatile fumes and do not use past the expiration date.
- Do not use if chemical pads show discoloration.
- Remove strips immediately before testing.
Reagent Strip Technique
- Dip the strip briefly (up to 1 second) into well-mixed, uncentrifuged urine at room temperature.
- Remove excess urine by gently touching the edge of the strip to the container.
- Blot the strip edge on a disposable absorbent pad.
- Allow specified time for color reactions before comparing to manufacturer's color chart in good lighting.
Automated Reagent Strip Readers
- Utilizes “Reflectance Photometry” for measurement.
Glucose Testing
- Principle: Employs a "Double Sequential Enzyme Reaction."
- Color change indicates positive presence: Green to brown.
- Reagents for Multistix include glucose oxidase, peroxidase, and potassium iodide; Chemstrip includes glucose oxidase, peroxidase, and tetramethylbenzidine.
- False positives may occur due to oxidizing agents or detergents.
- False negatives can occur with high ascorbic acid or ketone levels, high specific gravity, low temperatures, and poorly preserved specimens.
- Sensitivity threshold: 100 mg/dL.
Bilirubin Testing
- Principle: Based on the "Diazo Reaction."
- Positive color indication: Tan, pink, or violet.
- Major reagents include dichloroaniline for both Multistix and Chemstrip variations.
- False positives can arise from highly pigmented urine or certain medications.
- False negatives may occur due to specimen light exposure or high nitrite concentration.
Ketone Testing
- Principle: Involves "Sodium Nitroprusside Reaction (Legal’s Test)."
- Three forms of ketone bodies: Acetone (less sensitive), acetoacetic acid (most sensitive), and beta-hydroxybutyric acid (not detected by test).
- Positive indication: Purple color change.
- Reagents include sodium nitroprusside and glycine.
- False positives may result from certain medications or highly pigmented urine.
- False negatives can occur with improperly preserved specimens.
Specific Gravity Testing
- Principle: Measures change in pKa of a polyelectrolyte.
- Color indication: Blue at 1.000 to yellow at 1.030.
- Reagents vary between Multistix and Chemstrip versions.
- False positives can be due to high protein concentrations, while false negatives stem from highly alkaline urine.
Blood Testing
- Principle: Assesses "Pseudoperoxidase Activity of Hemoglobin."
- Color change indicates positive result: Uniform green/blue or speckled for intact RBCs.
- Reagents include various forms of tetramethylbenzidine.
- False positives may arise from strong oxidizing agents or contamination, while false negatives depend on specific gravity and specimen condition.
pH Testing
- Principle: Utilizes a "Double Indicator System."
- Color change from orange (pH 5.0) to blue (pH 9.0).
- Involves methyl red and bromthymol blue as reagents.
- No known interfering substances, but errors can occur from adjacent pad runover.
Protein Testing
- Principle: Relies on the "Protein Error of Indicators."
- Color change indicates protein presence: Blue.
- Reagents utilized in testing are specific to Multistix and Chemstrip.
- False positives may arise from overly alkaline urine or medications, while proteins other than albumin may lead to false negatives.
Urobilinogen Testing
- Principle: Identifies presence through the "Ehrlich Reaction."
- Positive result shows a cherry-red color.
- Major reagents include p-dimethylaminobenzaldehyde.
- False positives occur with Ehrlich-reactive compounds; false negatives may result from old specimens.
Nitrite Testing
- Principle: Utilizes the "Griess Reaction."
- Specific details on color indication and false results were not provided in the text.
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Description
This quiz covers the specifications, care, and techniques for using reagent strips in testing, primarily focusing on glucose testing methods. Understand proper storage, usage, and automated reading methods to ensure accurate test results. It's essential for laboratory technicians and students in health sciences.
