[False-positive reaction of urinary ketone bodies caused by bucillamine]

In many patients taking bucillamine, an anti-rheumatic drug, urinary examinations show false-positive findings for ketone on urine dipsticks, because of the SH radicals in bucillamine. Our group examined the frequency of false-positive ketone testing and the causative factors in 179 outpatients being treated by the Department of Rheumatology in our hospital. The samples that remained purple even after boiling were determined to be false-positives, because boiling volatilizes urinary ketones while leaving bucillamine unchanged. Forty-six of 49 patients taking bucillamine tested false-positive for ketone, whereas there were no false-positive reactions among patients not receiving bucillamine. The patients showing false-positive reactions had significantly lower serum albumin levels, higher specific gravity of urine and more acidic urine. Moreover, we could predict whether the reaction was true-positive or bucillamine-induced false-positive by observing differences between the colors and levels of discoloration of the urine test paper. In the evaluation of ketone findings on urinary dipstick, the physician must ascertain whether the patient is taking bucillamine.