Leukocytes in Urine (Leukocyte Esterase) Test Guide

What Is the Leukocyte Esterase (Leukocytes in Urine) Test?

I remember a patient, a 32-year-old woman who came to my clinic with a familiar complaint: “It burns when I pee, and I feel like I have to go all the time but nothing comes out.” A quick dipstick test showed a strong positive for leukocyte esterase, and a subsequent culture confirmed a urinary tract infection (UTI). That strip of plastic, with its little colored squares, is often the first clue we have in the fight against UTIs and other urinary tract disorders.

Leukocyte esterase is an enzyme produced by white blood cells (leukocytes). When this enzyme appears in urine, it signals that white blood cells are present—a classic marker of inflammation, usually due to infection. The test is a rapid, non-invasive screening tool that helps us decide whether further investigation (like a urine culture) is needed.

Why Is This Test Done?

In my clinical practice, I order the leukocyte esterase test as part of a routine urinalysis for patients with symptoms suggesting a UTI: dysuria (painful urination), urinary frequency, urgency, or suprapubic discomfort. It’s also used to monitor patients with known kidney infections, to screen pregnant women for asymptomatic bacteriuria, and to help rule out infection in febrile children or elderly patients with confusion.

How Is the Test Performed? (Sample & Specimen)

We ask for a clean-catch midstream urine sample to minimize contamination. The specimen is tested using a reagent strip (dipstick) that changes colour after a couple of minutes. The result is reported as negative, trace, 1+, 2+, or 3+, and the lab also often reports the degree of leukocyte esterase activity in cells/μL or using a semi-quantitative scale.

Reference Range: What Are Normal Values?

In a healthy individual, there should be no leukocyte esterase in the urine. A trace amount may be borderline and requires clinical correlation. The table below summarizes typical reference ranges by age and gender.

What Does a High Leukocyte Esterase Level Mean?

A positive leukocyte esterase test suggests the presence of white blood cells in urine—this is called pyuria. Most of the time, this points to a bacterial UTI caused by organisms such as E. coli, Klebsiella, or Proteus. However, other conditions can also cause pyuria: sexually transmitted infections (e.g., chlamydia, gonorrhoea), kidney stones, interstitial cystitis, or even strenuous exercise or catheterisation.

Can You Have Leukocytes in Urine Without Infection?

Yes, absolutely. In my practice, I sometimes see patients who are worried because their dipstick shows 2+ leukocyte esterase, but the culture comes back negative. This can happen with inflammation from non-infectious causes—such as glomerulonephritis, drug-induced interstitial nephritis (from NSAIDs or antibiotics), or even after a recent vigorous workout. It’s important not to assume infection based solely on the dipstick.

Leukocyte Esterase and Pregnancy

Pregnant women are routinely screened for asymptomatic bacteriuria because even without symptoms, a UTI in pregnancy can lead to pyelonephritis, preterm labour, and low birth weight. If leukocyte esterase is detected, we immediately send a urine culture. My patients often ask if a trace result is safe—I explain that guidelines vary, but most advise culture for any positive result in pregnancy.

Leukocyte Esterase in Children

Fever in a child without an obvious source often triggers a urinalysis. A positive leukocyte esterase in a young child is highly suspicious for a UTI, especially if accompanied by nitrites or symptoms. I remember one 3-year-old who had recurrent fevers; his leukocyte esterase was persistently positive, and an ultrasound later revealed vesicoureteral reflux. The test is a valuable red flag.

Symptoms That Often Accompany Leukocytes in Urine

If you have a positive leukocyte esterase result, pay attention to these possible symptoms: burning with urination, frequent need to urinate, feeling of incomplete bladder emptying, cloudy or foul-smelling urine, lower back or side pain, and sometimes fever. If you notice blood in your urine (haematuria), let your doctor know immediately.

Limitations of the Leukocyte Esterase Test

The dipstick test is a screening tool, not a diagnostic one. A false positive can occur if the sample is contaminated with vaginal secretions, in the presence of certain medications (e.g., cephalexin, nitrofurantoin), or if the urine is left at room temperature too long. False negatives happen if the urine is very dilute, if white blood cells are damaged, or if the patient has a very low white cell count (neutropenia).

In my practice, whenever the clinical suspicion is high—say, a patient with classic UTI symptoms but a negative dipstick—I still send a urine culture. It’s better to over-test than miss a hidden infection.

When Should You See a Doctor?

If your urinalysis shows leukocyte esterase and you have any of the symptoms described above, it’s wise to consult your doctor. Also speak up if you have recurrent UTIs, are pregnant, have diabetes or a compromised immune system, or if you’ve been catheterised. Early treatment prevents complications like kidney infection (pyelonephritis) or sepsis.

Remember: no online article can replace a face-to-face consultation. But knowing what your results mean can help you have a more informed conversation with your healthcare team.