A high white blood cell count in the urine is often a sign of an infection, states WebMD. The presence of either nitrites or leukocyte esterase means that when the lab examines the urine sample under a microscope, more white blood cells are present than normal.
Things that cause an elevated white blood cell count in the urine are pregnancy, urinary tract infection, kidney stones and a blockage in the urinary tract, according to WebMD. UTIs caused by bacteria generally reveal nitrites in a urine sample.
A lab examines the urine sample in three ways: a visual exam, a dipstick test and a microscopic exam, explains Mayo Clinic. The lab looks at the urine sample to see if it looks abnormal in relation to color and clarity. The lab does a dipstick test by placing a thin strip with chemicals on it into the urine. This strip reacts to the urine and tells the lab about things such as pH level, protein, sugar and any possible signs of infection. The lab then looks at a few drops of the urine under a microscope. If an elevated white count is seen under the microscope, further tests are ordered to see what the problem might be.