WBC esterase

Alternative names
Leukocyte esterase

Leukocyte esterase is a urine test for the presence of white blood cells and other abnormalities associated with infection.

How the test is performed

Child or adult:
Collect a “clean-catch” (midstream) urine sample. To obtain a clean-catch sample, men or boys will wipe clean the head of the penis. Women or girls will wash the area between the lips of the vagina with soapy water and rinse well. As you start to urinate, allow a small amount to fall into the toilet bowl. This clears the urethra of contaminants. Then, in a clean container, catch about 1 to 2 ounces of urine and remove the container from the urine stream. Give the container to the health care provider or assistant.

Thoroughly wash the area around the urethra. Open a Urine collection bag (a plastic bag with an adhesive paper on one end), and place it on your infant. For males, the entire penis can be placed in the bag and the adhesive attached to the skin. For females, the bag is placed over the labia. Diaper the infant as usual, covering the bag.

Check your baby frequently and remove the bag after the infant has urinated into it (for active infants, this procedure may take a couple of attempts, as they may displace the bag). Drain the urine into a container and give it to the health care provider.

How to prepare for the test
No special preparation is necessary for this test, but if the collection is being taken from an infant, extra collection bags may be necessary.

How the test will feel
The test will involve only normal urination, and there is no discomfort.

Why the test is performed
Leukocyte esterase is a screening test used to detect an enzyme that suggests the presence of leukocytes (white blood cells), and probably a urinary tract infection. This test is part of the routine dipstick test. If this test is positive, the urine should be examined microscopically for the presence of white blood cells and other abnormalities associated with infection.

Normal Values
A negative test result is normal.

What abnormal results mean
An abnormal result indicates a positive test and a possible urinary tract infection.

What the risks are
There are no risks.

Special considerations
False positive tests can be produced by contamination with vaginal secretions (such as blood or heavy mucus discharge), or by a Trichomonas infection (such as trichomoniasis).

False negative tests can be produced by the presence of high levels of protein or ascorbic acid (Vitamin C).

Johns Hopkins patient information

Last revised: December 4, 2012
by Janet G. Derge, M.D.

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