The inadequacy of urinary dipstick and microscopy as surrogate markers of urinary tract infection in urological outpatients with lower urinary tract symptoms without acute frequency and dysuria.

Purpose: Diagnosing urinary infection in patients with chronic lower urinary tract symptoms without dysuria is a critical step. In this study we scrutinize the sensitivity and specificity of dipstick urinalysis and microscopic pyuria (10 or more white blood cells per microl) to identify infection in such patients.

Materials And Methods: This was a prospective, blinded, observational cohort study of urological outpatients with painless lower urinary tract symptoms. Midstream and catheter urine samples were analyzed. A total of 508 midstream urine samples were used to compare leukocyte esterase, nitrite dipstick and urine microscopy with cultures seeking 10(5) cfu/ml. Similarly 470 catheter urine samples were used to compare the same surrogates with 10(5) cfu/ml and with an enhanced culture method seeking 10(2) cfu/ml. A comparison of leukocyte esterase against microscopic pyuria was made using the 508 midstream and 470 catheter specimens of urine. Midstream urine specimens were provided by 42 normal volunteers for comparison.

Results: For a midstream urine culture at 10(5) cfu/ml leukocyte esterase was 56% sensitive, nitrite was 10% sensitive and microscopic pyuria was 56% sensitive. Specificities were 66%, 99% and 72%, respectively. For a catheter specimen of urine culture at 10(5) cfu/ml leukocyte esterase was 59% sensitive, nitrite was 20% sensitive and microscopic pyuria was 66% sensitive. Specificities were 84%, 97% and 73%, respectively. The enhanced culture of catheter specimen of urine at 10(2) cfu/ml was positive in 29% of patients vs 15% at 10(5) cfu/ml.

Conclusions: Despite official guidelines and widespread use these tests cannot be considered appropriate for diagnosing urinary tract infection in patients with lower urinary tract symptoms, and should be abandoned in this context.