False 'hematuria' due to bacteriuria.

Abstract

To determine the effects of bacteriuria on dipstick urinalysis for microhematuria. Selection of urine samples with dipstick readings of at least one plus (+) for blood, followed by microscopic examination and bacterial culture, from patients with signs and symptoms of urinary tract diseases. A large teaching hospital in Melbourne, Australia. Two hundred forty-six inpatients and outpatients being investigated for signs and symptoms of urinary tract diseases. Seventeen (7%) of 246 patients having within-reference erythrocyte counts had polymicrobic cultures. One hundred nine patients had slight hematuria (1 x 10(7) to 6 x 10(7) cells/L). Of these, 21 bacteriuric patients had significantly higher dipstick findings than 88 abacteriuric patients (P < .005, Fisher's Exact Probability Test, two-tailed). Hydroperoxidase was detected in 80% of isolates (in 27 of 27 gram-negative bacilli cultures, in 6 of 6 staphylococci cultures, and in 3 of 12 streptococci cultures) on agar medium and in 69% of isolates in urine. These results show that patients without hematuria but with bacteriuria may give a false-positive dipstick reading for blood.