Low Sodium in Breast Cancer: What It Means and What to Do

Low sodium (hyponatremia) means the level of sodium in your blood is below normal, which can range from mild to life‑threatening depending on how low and how fast it drops. It’s something to take seriously, especially if you have symptoms like nausea, confusion, headache, or seizures. ^[1] Emergency care is recommended if severe symptoms occur, because hyponatremia can progress to seizures or coma. ^[2]

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Why Low Sodium Can Happen

• Cancer‑related triggers: Some cancers and their treatments can alter hormones that control water balance, leading to the body retaining water and diluting sodium. This pattern is often linked to SIADH (syndrome of inappropriate antidiuretic hormone secretion). ^[1]
• Medications: Several common medicines used during cancer care can lower sodium. Selective serotonin reuptake inhibitors (SSRIs) for mood/anxiety can cause SIADH and significant hyponatremia, which often improves when the drug is stopped. ^{[3] [4]} Desmopressin, sometimes used for bleeding control, can also cause severe hyponatremia if fluids aren’t restricted appropriately. ^[5]
• Chemo side effects: Vomiting, diarrhea, and poor intake during treatment can disturb electrolytes and lower sodium, so periodic blood tests are recommended during these times. ^{[6] [7]}
• Dehydration and fluid shifts: Cancer‑related dehydration from fever, sweats, or nausea can complicate fluid balance and contribute to sodium changes. ^[8]

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What Symptoms to Watch For

• Early signs: Nausea, headache, fatigue, muscle cramps, or irritability. These are common warning signs and should prompt a call to your care team if you’re at risk. ^[1]
• Serious signs: Confusion, vomiting, seizures, or loss of consciousness. These require urgent evaluation in the emergency department. ^{[9] [2]}

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When to Be Concerned

• Presence of symptoms: Any neurological symptoms (confusion, seizures) or worsening headache signal urgency, and emergency care is advised. ^[9]
• During treatment periods: If you’re receiving chemotherapy or new supportive medications, report symptoms early and ask about electrolyte checks, since imbalances are more likely. ^{[6] [7]}
• Older age or multiple medications: Older adults have higher risk of hyponatremia, especially with certain medicines. ^[10]

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How Low Sodium Is Evaluated

• Blood tests: Sodium level, kidney function, and serum osmolality. These confirm hyponatremia and assess severity. ^[11]
• Urine tests: Urine sodium and specific gravity help determine whether the cause is SIADH, dehydration, or other factors. This guides the treatment plan. ^[11]
• Clinical assessment: Checking for orthostatic blood pressure changes, swelling, and mucous membrane hydration helps evaluate your fluid status. ^[11]

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Treatment Options

• Symptom‑guided and gradual correction: Hyponatremia is typically managed in a monitored setting, and many cases need hospital care to correct sodium safely. ^[11]
• For severe cases: Hypertonic saline (3% sodium chloride) may be infused slowly until neurological symptoms improve, with careful monitoring to avoid complications from rapid correction. ^[11]
• Address the cause: Stopping or switching an offending medication (such as an SSRI) often reverses SIADH‑related low sodium. ^{[3] [4]} If desmopressin is involved, fluid restriction and close monitoring are essential. ^[5]
• Supportive care: During vomiting or diarrhea, frequent electrolyte checks and tailored IV or oral fluids help maintain balance. ^[6]

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Practical Steps You Can Take

• Know your symptoms: If you develop nausea, headache, cramps, unusual fatigue, or confusion during treatment, inform your oncology team promptly. ^[1]
• Review your meds: Share all prescriptions and supplements with your team, because some can lower sodium or interact during chemotherapy. ^[12]
• Hydration habits: Aim for steady fluid intake, and use electrolyte drinks during periods of vomiting or diarrhea as advised by your team. ^[7] Cancer care teams often recommend strategies to prevent dehydration around treatment days. ^{[13] [8]}
• Follow monitoring plans: If your team suggests periodic electrolyte panels, keep those appointments early detection prevents severe drops. ^{[7] [6]}

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Key Takeaways

• Hyponatremia can be mild or severe; the presence of neurological symptoms makes it urgent. ^{[9] [2]}
• Common contributors in breast cancer care include certain medications (like SSRIs), treatment side effects, and fluid balance changes such as SIADH. ^{[3] [4] [1]}
• Management focuses on safe correction and treating the underlying cause, often in a monitored setting. ^[11]
• Staying vigilant about symptoms and regular lab checks during treatment can reduce risks. ^{[6] [7]}