Which indicators are used to measure urine pH on dipstick tests, and what interference is common?

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Multiple Choice

Which indicators are used to measure urine pH on dipstick tests, and what interference is common?

Urine pH on dipstick tests is measured with a pair of indicators, methyl red and bromthymol blue, chosen because together they reliably cover the typical urine pH range. Methyl red responds in the acidic to mildly acidic range, while bromthymol blue shifts color as the solution becomes neutral to alkaline. Using both allows a single color on the pad to map to pH values from about 5 up to 9, which fits the usual urine acidity/alkalinity spectrum. A common interference is that alkaline urine can occur when the sample is old or has carried over from contamination. Bacteria in standing urine can metabolize urea to ammonia, raising the pH and giving a falsely alkaline reading. This kind of interference explains why the indicator setup is described as susceptible to alkaline shifts from old samples or carryover. The other options don’t fit because methyl orange alone isn’t the standard dipstick indicator for urine pH, and some choices imply no interference or use a different indicator (phenolphthalein) that isn’t used for routine dipstick pH testing.

Urine pH on dipstick tests is measured with a pair of indicators, methyl red and bromthymol blue, chosen because together they reliably cover the typical urine pH range. Methyl red responds in the acidic to mildly acidic range, while bromthymol blue shifts color as the solution becomes neutral to alkaline. Using both allows a single color on the pad to map to pH values from about 5 up to 9, which fits the usual urine acidity/alkalinity spectrum.

A common interference is that alkaline urine can occur when the sample is old or has carried over from contamination. Bacteria in standing urine can metabolize urea to ammonia, raising the pH and giving a falsely alkaline reading. This kind of interference explains why the indicator setup is described as susceptible to alkaline shifts from old samples or carryover.

The other options don’t fit because methyl orange alone isn’t the standard dipstick indicator for urine pH, and some choices imply no interference or use a different indicator (phenolphthalein) that isn’t used for routine dipstick pH testing.

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