Sodium 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 Sodium in Urine?
Sodium is the body's primary extracellular electrolyte, playing a central role in regulating blood volume, blood pressure, fluid balance, and nerve and muscle function. The kidneys are the master regulators of sodium balance, constantly adjusting how much sodium is reabsorbed from filtered blood back into circulation and how much is excreted in the urine. This regulation is mediated by hormones including aldosterone, antidiuretic hormone (ADH), and atrial natriuretic peptide (ANP), which respond to changes in blood volume and pressure to keep sodium levels within a narrow range.
A urine sodium test measures how much sodium the kidneys are excreting and provides critical diagnostic information about volume status, kidney function, and the cause of electrolyte abnormalities—particularly hyponatremia (low blood sodium), which is the most common electrolyte disorder in hospitalized patients. The test can be performed on a spot urine sample or a 24-hour collection. Spot urine sodium is most useful in acute clinical scenarios, while 24-hour sodium excretion reflects total daily sodium intake and is used for dietary assessment and chronic disease management.
Por que isso importa
Urine sodium is one of the most valuable tests for evaluating hyponatremia, acute kidney injury, and volume status in both outpatient and hospital settings. In hyponatremia, urine sodium distinguishes between different causes: low urine sodium (<20 mEq/L) suggests the body is retaining sodium because of volume depletion, heart failure, or cirrhosis, while high urine sodium (>40 mEq/L) points toward SIADH, adrenal insufficiency, or kidney disease. In acute kidney injury, urine sodium helps differentiate prerenal azotemia (where kidneys are underperfused but structurally intact) from intrinsic kidney damage. This distinction directly impacts treatment decisions.
Faixas de referência normais
| Grupo | Faixa | Unidade |
|---|---|---|
| Adults (24-hour) | 40–220 | mEq/day |
| Spot urine (variable) | 20–40 | mEq/L |
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 uNa
Causas comuns
- High dietary salt intake
- SIADH (syndrome of inappropriate antidiuretic hormone)
- Adrenal insufficiency (Addison disease)
- Salt-wasting nephropathy
- Diuretic use
- Cerebral salt wasting
- Acute tubular necrosis (recovering phase)
Possíveis sintomas
- Often reflects underlying condition rather than sodium excretion itself
- Headache and confusion (if hyponatremia develops)
- Nausea and vomiting
- Muscle cramps
- Low blood pressure (if volume depleted)
- Fatigue
O que fazer: High urine sodium in the setting of hyponatremia suggests SIADH, adrenal insufficiency, or renal salt wasting. Your doctor will check serum and urine osmolality, cortisol levels, and thyroid function to identify the cause. Treatment for SIADH includes fluid restriction and sometimes medications like tolvaptan. Adrenal insufficiency requires hormone replacement. If high urine sodium simply reflects high dietary intake, reducing salt consumption is recommended to protect blood pressure and cardiovascular health.
O que significam níveis baixos de uNa
Causas comuns
- Volume depletion or dehydration
- Congestive heart failure
- Liver cirrhosis with ascites
- Nephrotic syndrome
- Low dietary sodium intake
- Prerenal acute kidney injury
- Aldosterone excess (primary or secondary)
Possíveis sintomas
- Signs of the underlying condition (edema in heart failure, ascites in cirrhosis)
- Thirst
- Dizziness upon standing
- Reduced urine output
- Dry mucous membranes
- Rapid heart rate
O que fazer: Low urine sodium indicates the kidneys are retaining sodium in response to perceived volume depletion—whether actual (dehydration, hemorrhage) or effective (heart failure, cirrhosis). Treatment depends on the cause: volume-depleted patients need intravenous fluids, while patients with heart failure or cirrhosis need sodium and fluid restriction along with diuretics. Low urine sodium in the setting of acute kidney injury suggests prerenal causes that may respond to volume resuscitation, potentially avoiding more serious kidney damage.
Quando o exame de uNa é recomendado?
- When evaluating hyponatremia (low blood sodium)
- In the workup of acute kidney injury to determine the cause
- When assessing volume status in hospitalized patients
- To monitor dietary sodium intake and compliance
- When SIADH or adrenal insufficiency is suspected
- In the management of heart failure or cirrhosis
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.
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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.