Nitrites in Urine
UrináliseÚltima revisão: 7 de abril de 2026. Abordagem de fontes: contexto padrão de interpretação laboratorial, material médico de referência e orientações clínicas ou de saúde pública quando relevantes.
O que é Nitrites in Urine?
The nitrite test on a urine dipstick detects the presence of nitrites, which are produced when certain bacteria convert dietary nitrates (naturally present in urine) into nitrites through an enzymatic process. This conversion is performed by gram-negative bacteria, most commonly Escherichia coli, Klebsiella, and Proteus species—organisms that are responsible for the majority of urinary tract infections. A positive nitrite test therefore serves as a chemical indicator of bacterial infection in the urinary tract.
The nitrite test is one of the most specific indicators of a UTI on a standard urinalysis dipstick, with a specificity of approximately 95–98%. However, its sensitivity is lower, around 45–60%, meaning that a negative result does not rule out infection. This is because not all bacteria produce nitrites—gram-positive organisms like Enterococcus and Staphylococcus saprophyticus lack the enzyme needed for nitrate-to-nitrite conversion. Additionally, the bacteria need sufficient time in the bladder (typically 4 or more hours) to produce detectable nitrite levels, which is why a first-morning urine specimen provides the most reliable results.
Por que isso importa
A positive nitrite test is a highly reliable indicator that bacteria capable of causing a UTI are present in the urinary tract. When combined with a positive leukocyte esterase result, the predictive value for UTI exceeds 90%, allowing clinicians to begin empiric antibiotic treatment before culture results are available—which typically takes 24–48 hours. This rapid diagnosis is particularly valuable in settings like emergency departments and urgent care clinics where timely treatment prevents the progression of lower UTIs to more serious kidney infections. The test is also an inexpensive screening tool used in prenatal care to detect asymptomatic bacteriuria.
Faixas de referência normais
| Grupo | Faixa | Unidade |
|---|---|---|
| Normal | Negative | |
| Positive | Any positive result is abnormal |
As faixas de referência podem variar entre laboratórios. Sempre compare seus resultados com as faixas fornecidas pelo seu local de exame.
O que significam níveis altos de Nit
Causas comuns
- Urinary tract infection with gram-negative bacteria
- Asymptomatic bacteriuria
- Kidney infection (pyelonephritis)
- Catheter-associated UTI
- Contaminated or improperly stored urine sample
Possíveis sintomas
- Burning or painful urination
- Increased frequency and urgency of urination
- Cloudy or strong-smelling urine
- Lower abdominal or pelvic pain
- Fever and flank pain (kidney infection)
- May be completely asymptomatic
O que fazer: A positive nitrite test strongly suggests a bacterial UTI and typically warrants antibiotic treatment. Your doctor should order a urine culture with sensitivity testing to identify the specific organism and confirm the most effective antibiotic. Begin empiric antibiotics while awaiting culture results if symptoms are present. Increase fluid intake and complete the full course of prescribed antibiotics. Follow up with a repeat urinalysis if symptoms do not resolve within 48–72 hours of starting treatment.
O que significam níveis baixos de Nit
Causas comuns
- No significant bacterial infection present
- Infection with organisms that do not convert nitrate to nitrite
- Urine not in bladder long enough for conversion (recent frequent voiding)
- Low dietary nitrate intake
Possíveis sintomas
- No symptoms—a negative nitrite test is normal
O que fazer: A negative nitrite test is a normal finding. However, remember that a negative result does not completely exclude a UTI, especially if symptoms are present. If you have UTI symptoms with a negative nitrite test, your doctor may still order a urine culture or treat based on other findings such as positive leukocyte esterase or bacteria on microscopy.
Quando o exame de Nit é recomendado?
- When symptoms of a urinary tract infection are present
- As part of routine urinalysis screening
- During prenatal visits to screen for asymptomatic bacteriuria
- When monitoring response to UTI treatment
- In patients with recurrent UTIs
- When evaluating fever of unknown origin
Perguntas frequentes
Biomarcadores relacionados
Referências e abordagem de revisão
As páginas do glossário de biomarcadores são explicações educativas e devem ser interpretadas junto com as faixas de referência e observações fornecidas pelo seu laboratório e pelo seu médico. Para conhecer nossos padrões editoriais e processo de revisão, veja nossa Política editorial e a nossa revisão de conteúdo.
Quer analisar seus níveis de Nit?
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Enviar resultados de exames →Aviso médico: Estas informações são apenas educativas e não substituem orientação, diagnóstico ou tratamento médico profissional. As faixas de referência podem variar entre laboratórios. Sempre converse com seu profissional de saúde sobre a interpretação dos seus resultados específicos.