Leukocytes, commonly known as white blood cells, are a fundamental part of the body’s immune system, circulating to fight off infection and manage inflammation. During routine prenatal care, a urine test often checks for the presence of these cells, as their appearance in the urine can be an early warning sign. When elevated levels of leukocytes are detected in a pregnant person’s urine, it indicates an immune response is occurring somewhere in the urinary tract. This finding is common during pregnancy and triggers a necessary follow-up investigation to determine the exact cause, ensuring the health of both the expectant mother and the developing fetus.
Defining Pyuria and Leukocyte Presence
The medical term for an abnormally high concentration of leukocytes in the urine is pyuria. Leukocytes are the body’s first responders, traveling to the site of a perceived threat, such as an infection or inflammation. The urinary tract is typically sterile and should not contain a significant number of immune cells. While a small amount of leukocytes is normal, a count exceeding a specific threshold, such as ten white blood cells per cubic millimeter of urine, is defined as pyuria.
Pyuria signals that the body is actively mobilizing its defenses against an invader or injury, which can originate anywhere from the kidneys down to the urethra. For a pregnant individual, this finding is never ignored, even if no other symptoms are present. Physiological changes during pregnancy necessitate a lower threshold for concern regarding potential urinary tract issues.
Specific Reasons for Leukocytes During Pregnancy
The most frequent cause for elevated leukocytes is an infection within the urinary system. This includes symptomatic Urinary Tract Infection (UTI), which presents with discomfort like pain during urination or increased urgency. Of greater concern is Asymptomatic Bacteriuria (ASB), where bacteria are present in the urine without causing immediate physical symptoms. ASB is prevalent in pregnancy because hormonal changes relax the urinary tract muscles, leading to slower urine flow, known as urinary stasis.
Physiological changes also contribute to the heightened risk of infection. The enlarging uterus exerts pressure on the ureters, impairing drainage and creating an environment conducive to bacterial growth and ascent toward the kidneys. If pyuria is found but follow-up tests show no bacteria, this is referred to as sterile pyuria.
Sterile pyuria may be caused by organisms that do not grow on standard culture media, such as Chlamydia trachomatis. The urine sample can also be contaminated with vaginal discharge, which naturally contains white blood cells, leading to a false-positive result. Other non-infectious causes include kidney stones or inflammatory conditions.
Diagnostic Testing Following a Positive Screen
A routine urinalysis suggests the presence of leukocytes, typically through a dipstick test that detects the enzyme leukocyte esterase. This initial screen is a rapid indicator but is not definitive for diagnosing a bacterial infection. Further confirmation requires a more comprehensive test, starting with a clean-catch midstream urine sample to minimize external contamination.
The definitive diagnostic tool is the urine culture and sensitivity test. This test identifies the specific type and quantity of bacteria present. A positive culture confirms a bacterial infection by quantifying the bacterial colony count. The sensitivity portion determines which specific antibiotics will be effective against the identified strain of bacteria.
The culture is important because it distinguishes between harmless pyuria and a true bacterial threat. Only a positive culture confirms the presence of a uropathogen requiring antimicrobial treatment. If pyuria is present but the culture is negative, the healthcare provider investigates non-bacterial causes, such as sexually transmitted infections or other inflammatory processes.
Treatment and Maternal-Fetal Implications
Management of pyuria focuses on eradicating any confirmed bacterial infection due to the risks of progression. If Asymptomatic Bacteriuria or a symptomatic UTI is diagnosed, a course of pregnancy-safe antibiotics is immediately prescribed. Common first-line options include nitrofurantoin, cephalexin, or fosfomycin, all of which have established safety profiles during gestation.
Untreated urinary infections pose considerable risks to both the mother and the fetus. For the mother, the greatest danger is the ascent of the infection from the bladder to the kidneys, leading to pyelonephritis. Pyelonephritis is a serious kidney infection that occurs in up to 30% of untreated ASB cases and often requires hospitalization for intravenous antibiotics.
Fetal risks associated with untreated infection include an increased chance of preterm labor and delivery, as well as low birth weight. The inflammation triggered by infection can stimulate uterine contractions, initiating labor prematurely. Following the antibiotic course, a “test of cure” urine culture is routinely performed to confirm that the bacterial infection has been cleared.