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Correct Answer: decreased nitrites
when urine is not preserved and remains at room temperature, several chemical and physical changes can occur over time due to bacterial growth and chemical reactions. these changes can significantly impact the accuracy of urine tests if the sample is analyzed after a prolonged period. this explanation discusses why "decreased nitrites" is not a typical change in unpreserved urine, contrary to the other changes listed.
**increased ph:** the ph of urine typically increases (becomes more alkaline) when it is left unpreserved. this change occurs because urea, a major component of urine, is broken down by urease-producing bacteria into ammonia, which increases the ph. this alkaline shift can affect the solubility and stability of other substances in the urine.
**increased bacteria:** bacterial contamination is common in urine samples that are not immediately processed or preserved. bacteria can multiply rapidly in urine at room temperature, leading to alterations in the composition of the urine, including the consumption or production of various substances.
**increased nitrites:** contrary to the option suggesting "decreased nitrites," the concentration of nitrites in urine typically increases when it is not preserved. this increase is due to the action of certain bacteria that convert nitrate (present in urine) to nitrite. the presence of nitrites in urine is commonly used as an indicator of bacterial infection (e.g., urinary tract infection).
**decreased glucose, urobilinogen, ketones, and bilirubin:** these substances can decrease in concentration in unpreserved urine. bacteria may consume glucose and ketones as energy sources, while bilirubin and urobilinogen can be broken down or altered by light or bacterial action.
**formed element destruction:** cells and other formed elements, such as casts in urine, can degrade over time when urine is not preserved. this degradation is due to enzymatic activity and osmotic changes that cause cells to lyse or disintegrate.
**change in color:** the color of urine can change upon standing due to the oxidation of certain compounds and the growth of bacteria, which may produce pigmented substances.
in conclusion, the correct answer to the question about changes in unpreserved urine is that "decreased nitrites" is not expected; rather, nitrites are likely to increase. understanding these changes is crucial for ensuring accurate diagnostic results in medical tests involving urine samples.
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