False positive results for leucocytes in urine dipstick test with common antibiotics

We found positive results for leucocyte esterase in the dipstick test in two patients with acute leukaemia who had had documented aplasia for several days. They were treated with imipenem for fever of unknown origin and had no symptoms of urinary tract infection; the sediment and culture were negative. The dipstick test for leucocyte esterase was also positive in vitro with imipenem, and this prompted us to investigate further. We dissolved the antibiotics to be tested as recommended by the manufacturers at the concentrations used for infusion or more dilute (table 1). The drugs were used in their commercially available form or provided as single substances by the manufacturers. Spontaneous degradation (aging) was allowed for by …