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Questions and Answers
Which of the following can lead to a false negative result for the nitrite test on a urine reagent strip?
Which of the following can lead to a false negative result for the nitrite test on a urine reagent strip?
- Highly pigmented urine
- Insufficient contact time between bacteria and urinary nitrate (correct)
- High specific gravity
- Presence of antibiotics
Which of the following can cause a false positive result for the leukocyte esterase test on a urine reagent strip?
Which of the following can cause a false positive result for the leukocyte esterase test on a urine reagent strip?
- Presence of p-aminosalicylic acid
- Presence of sulfonamides
- Presence of chlorpromazine
- Presence of methyldopa (correct)
Which of the following is the LEAST likely cause of a false positive nitrite test on a urine reagent strip?
Which of the following is the LEAST likely cause of a false positive nitrite test on a urine reagent strip?
- Presence of nonreductase-containing bacteria
- Presence of high concentrations of ascorbic acid
- Presence of large quantities of bacteria converting nitrite to nitrogen
- Presence of highly pigmented urine (correct)
Which of the following is the MOST likely cause of a false positive leukocyte esterase test on a urine reagent strip?
Which of the following is the MOST likely cause of a false positive leukocyte esterase test on a urine reagent strip?
Which of the following is the LEAST likely cause of a false negative nitrite test on a urine reagent strip?
Which of the following is the LEAST likely cause of a false negative nitrite test on a urine reagent strip?
Which of the following can cause both a false positive nitrite test and a false positive leukocyte esterase test on a urine reagent strip?
Which of the following can cause both a false positive nitrite test and a false positive leukocyte esterase test on a urine reagent strip?
Which of the following is the LEAST likely cause of a false positive leukocyte esterase test on a urine reagent strip?
Which of the following is the LEAST likely cause of a false positive leukocyte esterase test on a urine reagent strip?
Which of the following is the MOST likely cause of a false negative leukocyte esterase test on a urine reagent strip?
Which of the following is the MOST likely cause of a false negative leukocyte esterase test on a urine reagent strip?
Which of the following is the LEAST likely cause of a false positive result for the nitrite test on a urine reagent strip?
Which of the following is the LEAST likely cause of a false positive result for the nitrite test on a urine reagent strip?
Which of the following is the MOST likely cause of a false positive result for the leukocyte esterase test on a urine reagent strip?
Which of the following is the MOST likely cause of a false positive result for the leukocyte esterase test on a urine reagent strip?
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Study Notes
Leukocyte Esterase Reagent Strip
- Multistix: detects 5-15 WBC/hpf, Chemstrip: detects 10-25 WBC/hpf
- False positive results can occur due to high concentrations of protein, highly alkaline urines (pH > 6.5), and presence of nitrite
Specific Gravity Reagent Strip
- Based on the principle of change in pKa of polyelectrolytes in an alkaline medium
- Uses bromthymol blue as an indicator to measure pH changes
- Multistix and Chemstrip use different reagents, including poly (methyl vinyl ether/maleic diaminoethyl anhydride) and ethylene glycol ether, respectively
- False positive results can occur due to strong oxidizing agents, formalin, and highly pigmented urine, nitrofurantoin
- False negative results can occur due to high protein concentrations, oxalic acid, ascorbic acid, gentamicin, cephalosporins, and tetracyclines
- Correlation: as specific gravity increases, the indicator changes from blue to yellow (1.000 to 1.030)
Ascorbic Acid
- Principle: action of ascorbic acid to reduce a dye in the impregnated pad
- Can detect AA concentration as low as 7.0 mg/dl and consistently detect 20 mg/dl of AA in 90% urine tested
- High levels of AA cause false-negative results on glucose, blood, bilirubin, nitrite, and leukocyte esterase tests
Benedict's Test (Glucose and Reducing Sugars)
- Principle: copper reduction
- False-negative results can occur due to high levels of ascorbic acid (>25mg/dL)
- Reporting: grades of negative, trace, 1+, 2+, 3+, and 4+, with corresponding colors and characteristics
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