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Kidney

Leukocytes in urine: result and a falsely negative test strip

Leukocytes, also called white blood cells, are immune cells that help protect the body against foreign invaders. When the kidneys, the bladder or the urinary tract become inflamed, more of these cells end up in the urine.

An inflammation of the urinary tract can cause urgency, visible blood in the urine or tenderness above the pubic bone. Only a urine test can establish whether immune cells are present in the urine.

The score on the test strip runs from negative through trace to +, ++ and +++, and negative is the expected result. A negative strip carries less weight with very concentrated urine or after vitamin C or antibiotics, because those can keep the pad falsely negative.

Doctor's Assessment Included

Leukocytes are white blood cells, the cells that fight infection; the leukocyte strip looks in the urine for an enzyme they release, and normally the result is negative.

  • A positive leukocyte strip fits inflammation of the kidneys, bladder or urinary tract, but it is not a diagnosis: nitrite, symptoms and a urine culture count too.
  • The leukocyte strip misses some infections: in studies it was positive in 72 to 97 percent of proven urinary tract infections.
  • Above 65 the leukocyte strip is less reliable, because bacteria and white blood cells in the urine without infection become more common.

Reference Ranges

Expected result Negative

Reference ranges may vary between laboratories. When you order a test, a BIG-registered doctor assesses your personal results in context. For treatment decisions, discuss your results with your GP.

Urine Leukocytes: what this test measures

The leukocyte pad on the test strip reacts to leukocyte esterase, an enzyme that comes from neutrophils, one of the types of white blood cell. The colour and strength of the pad are read as a score.

Contamination during collection can make it falsely positive. It can turn falsely negative with urine of a high specific gravity, meaning very concentrated urine, with a lot of glucose or protein in the urine, with vitamin C, and with some antibiotics such as cephalexin, nitrofurantoin, tetracycline and gentamicin.

Leukocytes in the urine are a different test from the leukocytes in the blood, which are counted in a blood sample; the urine cells themselves are counted under a microscope in a urine sediment.

Urine Leukocytes: why this value matters

A negative leukocyte strip is not fully reassuring: studies found a positive strip in 72 to 97 percent of culture-confirmed infections.

A positive leukocyte strip can point to immune cells in the urinary tract, but the strip does not say why those cells are there.

Urine Leukocytes: how the blood test works

Referral
No GP referral needed. After the order we arrange the referral through ZorgDomein, within one business day; orders after 17:00 or at the weekend start on the next business day. ZorgDomein emails a barcode, and that barcode is what the draw site needs.
The draw
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Where
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Urine Leukocytes: when is testing worthwhile?

Under the UK guidance, women under 65 with just one symptom out of pain when passing urine, cloudy urine and new night-time urination get a leukocyte strip. In men under 65 in whom a urinary tract infection is suspected, with little risk of complications and no catheter, the strip is unreliable for ruling out an infection according to that guidance, and above 65 the same guidance calls test strips unreliable for the diagnosis.

The leukocyte pad also sits on the strip of a broader urine examination, next to nitrite, blood, protein and glucose, among others.

Urine Leukocytes: symptoms of a high or low value

Low Levels

A negative leukocyte strip, the expected result, says less when vitamin C or some antibiotics have suppressed the pad.

High Levels

Flank pain with fever and shivering next to a positive leukocyte strip can point to a kidney infection and is a reason to call a doctor.

Urine Leukocytes: causes of a low or high value

What lowers the value

  • Vitamin C

    Vitamin C in the urine can make the leukocyte strip falsely negative.

  • Concentrated urine, glucose or protein

    Very concentrated urine, or a lot of glucose or protein in the urine, can make the leukocyte strip falsely negative.

  • Some antibiotics

    Some antibiotics, such as nitrofurantoin, tetracycline and gentamicin, can make the leukocyte strip falsely negative.

What raises the value

  • Urinary tract infection

    In a bladder or other urinary tract infection, leukocytes can often be detected in the urine; together with a positive nitrite test they suggest a urinary tract infection.

  • A sexually transmitted infection such as chlamydia

    A sexually transmitted infection such as chlamydia can put leukocytes in the urine while an ordinary urine culture grows nothing.

  • Inflammation without bacterial growth

    Leukocytes in the urine with no growth in the culture can fit, among other things, an earlier course of antibiotics, a catheter, urinary stones or a bladder tumour.

  • Bacteria and white cells without infection in older adults

    Above 65, more and more people have bacteria and white blood cells in the urine without an infection; this can make the leukocyte strip positive, and antibiotics do not help then.

  • Contaminated urine sample

    Urine that was not caught cleanly can make the leukocyte strip falsely positive.

Urine Leukocytes: lifestyle and this value

A positive leukocyte strip can point to a urinary tract infection, and for that infection the UK guidance advises seeking advice again when symptoms worsen after a consultation or are not better after 48 hours.

Urine Leukocytes: frequently asked questions

What is a normal result for leukocytes in urine?

A normal result for leukocytes in urine is negative. The strip gives a score instead of a number, negative, trace, +, ++ or +++, and on its own that score says nothing about the cause.

Can concentrated urine distort the leukocyte strip?

Yes, very concentrated urine can keep the leukocyte strip falsely negative. Review articles name urine with a high specific gravity as a cause of a falsely negative result, so a negative strip with such urine is less certain.

Does vitamin C interfere with the leukocyte test strip?

Yes, vitamin C can keep the leukocyte pad falsely negative. A negative result after vitamin C can therefore be wrongly reassuring, and the same holds for some antibiotics, such as cephalexin and nitrofurantoin.

What is the difference between leukocytes in urine and in the blood?

Leukocytes in urine and leukocytes in the blood are two separate tests from two different samples. The urine strip looks for an enzyme from white blood cells in the urine, while the blood value counts the white blood cells in the blood.

Urine Leukocytes: sources

  1. Hitzeman N, Greer D, Carpio E. Office-Based Urinalysis: A Comprehensive Review. Am Fam Physician 2022;106(1):27-35B. (retrieved 2026) aafp.org
  2. Simerville JA, Maxted WC, Pahira JJ. Urinalysis: a comprehensive review. Am Fam Physician 2005;71(6):1153-1162. (retrieved 2026) aafp.org
  3. UK Health Security Agency. Diagnosis of urinary tract infections: quick reference tools for primary care, updated 7 July 2025. (retrieved 2026) gov.uk

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