Which of the following is correct regarding the presence of leukocyte esterase in a urinalysis dip test?
(A) Positive test indicates definite presence of leukocytes.
(B) Negative test rules out presence of leukocytes.
© Positive test indicates presence of organisms that reduce
nitrate to nitrite.
(D) Positive test is suggestive of bacteria.
(E) Positive test indicates presence of blood.
The answer is D. A positive test for leukocyte esterase is suggestive, but not diagnostic, of bacteria. To be sure,the inference is based on the presumed presence of leukocytes (WBCs). Leukocyte esterase is an enzyme elaborated by WBCs. However, its sensitivity is compromised by the false negatives that can be produced by high specific gravity of the urine, glycosuria, presence of urobilinogen, and medications including rifampin and ascorbic acid. Furthermore, false positives are produced by specimen contamination. There is a separate dip test for organisms thatreduce nitrate to nitrite. They include many Gram-negative bacteria but not all. The sensitivity of the nitrite test is only 30%.