Anthony Ofori | Medical Graduate in General Medicine | Founder, WellNest Central
Last updated: October 29, 2026
General health information, not individualized diagnosis or treatment.
Low sodium in the blood, called hyponatremia, means the measured sodium concentration is below the laboratory’s reference range. It often reflects a change in the balance between water and sodium rather than simply eating too little salt. The cause, speed of development, symptoms, and medical history determine the urgency.
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What sodium does
Sodium is an important electrolyte involved in fluid distribution, nerve impulses, and muscle function. Blood sodium is tightly regulated by hormones, the kidneys, and thirst. When the balance is disrupted, cells may swell as water shifts between compartments. Brain cells are particularly sensitive to rapid changes, which is why some cases require urgent evaluation.
What counts as low sodium
Many laboratories define hyponatremia as a blood sodium concentration below about 135 milliequivalents per liter, but reference intervals can vary. The number alone does not reveal the cause. Clinicians consider whether the level is mildly or severely reduced and whether it has developed quickly or over time. A result should be interpreted with symptoms and other tests.
Symptoms to recognize
Mild or chronic reductions may produce no obvious symptoms. Other people experience nausea, headache, weakness, difficulty concentrating, or unsteadiness. Severe or rapidly developing hyponatremia can cause confusion, seizures, reduced consciousness, and other dangerous neurologic symptoms. Emergency symptoms require immediate medical care rather than attempting to correct sodium at home.
Common causes
Certain diuretics, particularly thiazide-type medicines, can cause low blood sodium. Other possibilities include vomiting, diarrhea, heart failure, liver disease, kidney conditions, hormone disorders, and the syndrome of inappropriate antidiuretic hormone secretion. Drinking large quantities of water under certain conditions can also lower sodium. The mechanism varies and directly affects treatment choice.
Why fluid status matters
Two people can have the same sodium result but very different fluid states. A person may be dehydrated, retain excess water because of heart or liver disease, or appear to have a normal fluid volume. Examination and laboratory tests help distinguish these situations. Treating all cases by drinking more water or consuming salt packets can make some conditions worse.
Testing and assessment
As explained in MedlinePlus guidance on sodium testing, sodium measurements are interpreted with fluid balance and other clinical findings. If several electrolytes are abnormal, our guide to low potassium blood-test results provides useful context about why each result requires a separate assessment.
Depending on symptoms and history, assessment may include repeat serum electrolytes, glucose, kidney function, serum and urine osmolality, urine sodium, and medication review. Blood glucose can affect the measured sodium concentration. Endocrine evaluation may be appropriate in selected cases. Testing is guided by the clinical situation rather than one universal panel.
Treatment depends on the cause
Treatment may involve adjusting medications, treating an underlying illness, controlled fluid restriction, intravenous fluids, or specialized monitoring. Severely symptomatic patients require hospital care. Correcting chronic sodium deficiency too rapidly can cause serious neurological injury, so correction rates must be supervised. Do not attempt to rapidly raise blood sodium with supplements or salt without professional guidance.
Prevention and follow-up
Follow medication instructions and recommendations for hydration appropriate to your activity and medical conditions. Endurance athletes should avoid excessive fluid consumption beyond needs, and people on diuretics may require monitoring. Repeat testing may be necessary after treatment. Sudden confusion, seizures, or loss of consciousness requires emergency services.
Frequently asked questions
Does low sodium mean I should eat more salt? Not necessarily; the problem can be excess water or an underlying condition. Can drinking too much water cause low sodium? Yes, under certain circumstances, especially when the body cannot excrete water quickly enough.
What the sodium result cannot tell you alone
A laboratory sodium value reflects concentration rather than the total amount of sodium in the body. Too much retained water can dilute sodium, while fluid losses may also produce low sodium under some conditions. This explains why simply adding table salt is not a universal treatment. Clinicians often assess fluid status, medicine use, and associated laboratory measurements to establish the mechanism.
Symptoms can depend on both the sodium level and how rapidly it changed. Chronic mild hyponatremia may be discovered during routine testing, while a rapid decline may cause significant neurologic symptoms. Headache, nausea, confusion, and seizures require different levels of urgency. A severely symptomatic person needs emergency medical assessment instead of an online home correction plan.
Medication review is especially important. Diuretics, some antidepressants, and other drugs may contribute in susceptible patients. Heart, kidney, liver, and hormone-related illnesses can also alter the body’s handling of salt and water. Clinicians may order urine sodium and osmolality tests to clarify the cause, but these results must be interpreted in context.
Treatment is often closely monitored because overly rapid correction of chronic hyponatremia can damage the nervous system. Fluid restriction is appropriate in some situations but harmful or insufficient in others. The safest plan depends on the cause and severity. Follow-up testing helps confirm that sodium is moving in the intended direction without causing complications.
What to remember
A low sodium concentration may arise because of excess water, fluid losses, medications, or underlying organ or hormone disorders. The appropriate treatment depends on the mechanism; simply eating more salt does not reliably correct the problem. Clinicians may assess blood glucose, kidney function, serum and urine osmolality, and medication use. Severe confusion, seizures, or impaired consciousness require emergency care. In significant or chronic hyponatremia, sodium must be corrected carefully because rapid correction can cause serious neurological injury. Follow-up testing helps confirm a safe response.
Key takeaways
Low sodium can arise for several different reasons. The urgency depends on symptoms, severity, and timing. Avoid attempting rapid correction yourself, and seek urgent care for serious neurological symptoms.
For individualized health concerns, book a personal consultation with WellNest Central.
