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.
