An evaluation of numerous reported studies indicated that the most useful screening tests for significant bacteriuria appear to be a nitrite test (modified by adding nitrate and incubating at 37 C), the triphenyltetrazolium chloride (TTC) test, and microscopic examination for bacteria. A study of 1,151 urine specimens submitted for routine culture showed that microscopic examination of the centrifuged deposit for organisms or pus cells, or both, was a more sensitive test for significant bacteriuria than the modified nitrite test. Microscopic examination detected 98% of 175 urine specimens with significant gram negative bacilluria, and 17 of 20 with significant numbers of gram positive cocci. The false positive rate was 13%. Microscopy may be better than the chemical screening tests in the selection of urine specimens for cultural examination.
Sacks TG, Abramson JH. Screening Tests for BacteriuriaA Validity Study. JAMA. 1967;201(1):1–4. doi:10.1001/jama.1967.03130010027005