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NITRITES
Nitrites normally are not found in urine but result when bacteria reduce urinary nitrates to nitrites. Many gram-negative and some gram-positive organisms are capable of this conversion, and a positive dipstick nitrite test indicates that these organisms are present in significant numbers (i.e., more than 10,000 per mL). This test is specific but not highly sensitive. Thus, a positive result is helpful, but a negative result does not rule out UTI.6 The nitrite dipstick reagent is sensitive to air exposure, so containers should be closed immediately after removing a strip. After one week of exposure, one third of strips give false-positive results, and after two weeks, three fourths give false-positive results.36 Non-nitrate–reducing organisms also may cause false-negative results, and patients who consume a low-nitrate diet may have false-negative results.
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