Low Sodium in Cancer: What It Means and When to Act

Low sodium in the blood (hyponatremia) is relatively common in people with cancer and can range from mild and asymptomatic to severe and life‑threatening. It deserves attention because it can affect thinking, energy, and overall outcomes, and sometimes signals an underlying issue that needs prompt care. ^[1] [PM9]

What “Low Sodium” Means

• Sodium helps regulate fluid balance and nerve/muscle function. When sodium drops, excess water shifts into cells and causes swelling, including in brain cells, which can lead to neurologic symptoms. ^[2]
• In cancer, hyponatremia can occur due to the cancer itself, treatments, or other medical problems. It is linked to worse prognosis if not addressed, but improvement in sodium levels is associated with better survival. [PM9] [PM8]

Why Cancer Increases Risk

• Some tumors (especially small cell lung cancer) can produce antidiuretic hormone inappropriately, causing water retention and low sodium; this is called SIADH (syndrome of inappropriate antidiuretic hormone secretion). SIADH is a frequent cause of low sodium in oncology and requires specific evaluation and management. [PM7] [PM10]
• Certain chemotherapy agents can injure the kidneys or trigger SIADH. Cisplatin has been reported to cause electrolyte losses and SIADH, which can contribute to hyponatremia. ^[3]
• Other common contributors in cancer care include nausea/vomiting, diarrhea, poor intake, dehydration, and medications. These issues can disturb fluid and electrolyte balance and set up conditions for sodium to drop. ^{[4] [5]}

Symptoms: Mild to Severe

• Mild to moderate symptoms may include nausea, headache, low energy, drowsiness, muscle cramps, and irritability. These can be subtle and easily mistaken for treatment side effects. ^{[6] [7]}
• Severe symptoms include confusion, seizures, and loss of consciousness. These are medical emergencies and need urgent care. ^{[8] [6]}

When to Seek Care

• If you develop significant nausea/vomiting, confusion, seizures, or pass out, seek emergency care immediately, as these may be signs of severe hyponatremia. ^{[8] [6]}
• If you are at risk (on chemo, lung cancer, known SIADH) and notice headaches, cramps, weakness, or unusual fatigue, contact your healthcare team promptly to check your sodium and fluid status. ^[7]

How Doctors Evaluate It

• Clinicians assess symptoms, recent treatments, fluid intake, and medications, then check blood tests (sodium and other electrolytes) and sometimes urine sodium/osmolality to pinpoint the cause. A structured evaluation helps distinguish SIADH from dehydration or kidney losses, guiding safe correction. [PM10] [PM24]

Treatment Options

Treatment aims to correct sodium safely and fix the underlying cause. The approach depends on how fast sodium fell, symptom severity, and your volume status (too much, too little, or normal body water). [PM11] [PM24]

• Acute, symptomatic hyponatremia (confusion, seizures):
  • Hypertonic saline in the hospital is typically used to raise sodium carefully and prevent brain complications. [PM7] [PM11]
• Chronic or milder SIADH:
  • Fluid restriction is often first‑line to reduce excess water retention. [PM7] [PM11]
  • If restriction is not enough or impractical, vasopressin receptor antagonists (vaptans, such as tolvaptan) may be considered to increase free water excretion without major electrolyte shifts. [PM7] [PM11]
• If kidney injury or drug effects are involved:
  • Adjusting or pausing the causative medication and replacing electrolytes can restore balance. ^[3]
• Supportive care:
  • Managing nausea, vomiting, and diarrhea, and maintaining appropriate hydration and electrolyte intake helps prevent recurrences. ^{[4] [5]}

Why It Matters

• Hyponatremia is not only uncomfortable; it can delay or interrupt cancer treatments and is associated with worse outcomes if persistent. [PM9]
• Encouragingly, when low sodium is identified and corrected, survival and treatment tolerance can improve. [PM8]

Practical Tips You Can Use

• Track symptoms: If you feel unusually tired, foggy, or have headaches/cramps, let your care team know these may be early clues. ^[6]
• Monitor fluids wisely: Avoid excessive water intake if you’ve been told you have SIADH; follow your team’s fluid guidance. [PM10]
• Address GI losses: Report ongoing vomiting or diarrhea promptly to prevent dehydration and electrolyte problems. ^[4]
• Medication review: Ask whether any of your current drugs could lower sodium and if adjustments are needed. [PM10]
• Know the red flags: Confusion, seizures, or passing out warrant emergency evaluation for possible severe hyponatremia. ^{[8] [6]}

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Do you have recent sodium lab values or symptoms like headaches, confusion, nausea, or cramps that you’re worried about? 궁금한 점 있으면 언제든 퍼슬리에 물어보세요.