MLT GlobeUrinalysis & Body Fluids: Urine chemical (dipstick)
49 Urinalysis & Body Fluids MCQs on Urine chemical (dipstick) with answers and explanations.
A random urine sample from a healthy adult on a mixed diet typically has a pH of about:
Urine pH normally ranges 4.5–8.0 and averages about 6.0 because the kidney excretes the daily acid load. A pH of 9 suggests an old sample with urease-producing bacteria.
Which sugar gives a negative copper-reduction (Benedict) test in urine?
Sucrose has no free anomeric carbon, so it is non-reducing. Fructose, galactose and arabinose are reducing sugars and give a positive result.
The reagent strip protein pad is based on which principle?
At a fixed pH of about 3, the indicator (tetrabromphenol blue) changes colour when protein, mainly albumin, accepts hydrogen ions. This is the protein error of indicators.
The glucose pad on a reagent strip uses which enzyme system?
Glucose oxidase produces hydrogen peroxide, which peroxidase uses to oxidise a chromogen. The reaction is specific for glucose.
A patient with hemolytic anemia is expected to have:
Excess unconjugated bilirubin is not water-soluble and does not appear in urine, but more is converted to urobilinogen in the gut and excreted in urine.
A urine sample left uncovered at room temperature and in light for several hours may give a false-negative result for:
Bilirubin is photo-oxidised to biliverdin on exposure to light, which does not react on the pad. Urobilinogen is also unstable and oxidises to urobilin.
A urine specimen kept at room temperature for 6 hours before testing will most likely show:
Bacteria multiply, consume glucose and produce ammonia from urea, raising pH. Casts and cells may also lyse. Urine should be tested within 2 hours or refrigerated.
The reagent strip blood pad detects hemoglobin through:
Heme has peroxidase-like activity that breaks down the pad's hydrogen peroxide and oxidises a chromogen. Strong oxidising contaminants such as bleach can therefore cause false-positive results.
Which reagent strip pad requires the longest reaction time, about 2 minutes, before reading?
The leukocyte esterase reaction is slow and is read at about 2 minutes; most other pads are read between 30 and 60 seconds.
The nitrite pad of a reagent strip is based on which reaction?
Nitrite reacts with an aromatic amine to form a diazonium salt, which couples with a second compound to give a pink colour. Peroxidase activity is the basis of the blood pad.
The reagent strip pH pad uses a double indicator system of:
Methyl red and bromthymol blue give a colour range from orange to blue across pH 5 to 9. Tetrabromphenol blue is the protein pad indicator.
Which reagent strip technique is correct?
The strip is dipped briefly so all pads are wet, and excess is removed to prevent run-over. Prolonged dipping leaches reagents from the pads.
The reagent strip protein pad is most sensitive to which protein?
The protein-error-of-indicators pad reacts mainly with albumin and is much less sensitive to globulins and free light chains (Bence Jones protein).
A positive nitrite test on a reagent strip indicates:
Many Gram-negative urinary pathogens, especially Enterobacterales such as E. coli, reduce dietary nitrate to nitrite, so a positive nitrite suggests bacteriuria.
Which urine specimen is preferred for routine urinalysis because it is the most concentrated?
The first morning urine has been in the bladder overnight, so it is concentrated and best for detecting substances and formed elements present in small amounts.
How should urine reagent strips be stored?
Moisture, light, heat and volatile chemicals damage the reagent pads. Strips are kept in their capped container with desiccant and are not refrigerated or frozen.
In a healthy adult, the reagent strip glucose result is normally:
Filtered glucose is almost completely reabsorbed by the proximal tubule, so normal urine gives a negative glucose pad.
In healthy people, the urine urobilinogen result on a reagent strip is usually:
Some urobilinogen formed in the gut is reabsorbed and excreted in urine, so a small amount (up to about 1 mg/dL, 1 EU) is normal. Strips cannot reliably detect its absence.
Which substances can give a positive reagent strip blood pad?
The blood pad uses the pseudoperoxidase activity of heme, which is present in hemoglobin (free or in red cells) and in myoglobin.
A false-negative nitrite test in a patient with a UTI is most likely when:
Bacteria need about 4 hours in the bladder to convert nitrate to nitrite, and Enterococcus and yeasts do not. A first morning sample is best. Standing at room temperature can cause false positives.