Leukocyte (WBC) esterase is an enzyme found in white blood cells (leukocytes) and is used as a marker for the presence of inflammation or infection in the urinary tract.
It can be measured in a urine test to help diagnose conditions such as urinary tract infections (UTIs) or bladder infections. A positive result for leukocyte esterase in urine indicates the presence of white blood cells in the urine, which is a sign of infection or inflammation. It is also used as a screening test along with other urine tests (such as nitrite test) to identify UTIs.
The normal value for leukocyte esterase is zero or 0. A color change in the dipstick indicator indicates the possible presence of an infection or inflammation (pyelonephritis, cystitis, urethritis, prostatitis, kidney stones, or acute glomerulonephritis are some of the possible causes.
Other causes of an increased Leukocyte esterase are retained foreign body, dehydration, fever or stress.
Dr. Weatherby's Urinalysis Book is a good source of information for the biomarkers found on a Urine Dipstick test:
https://www.amazon.com/Urinalysis-Book-Dicken-Weatherby/dp/0976136791