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False-Positive and False-Negative Ketone Test Results

Drugs containing free-sulfhydryl groups such as captopril ( an antihypertensive drug) and D-penicillamine (an antibiotic) can produce false-positive ketone results on the reagent strip. Highly pigmented urine can also produce a false-positive result.
Prolonged room temperature storage of the urine specimen can cause a false-negative test result for ketones. Urine specimens should not be stored at room temperature for more than two hours.