Hyponatremia means the sodium in your blood is too low.
It is the most common electrolyte abnormality in medicine, and it is almost never a sodium problem.
If you were told to eat more salt, the wrong question was asked
A low sodium result does not mean your body lacks sodium. In most patients the total body sodium is normal, or even high. What has changed is the water — there is too much of it, diluting a sodium content that was never the problem.
The number on the lab report is a ratio. It measures concentration, not quantity. Read it as a sodium deficit and you will treat a patient who has too much water by giving them more salt, which does nothing to the water.
The question is not why is the sodium low. The question is why is the body retaining water it should be excreting — and the answer is different for a patient on a thiazide, a patient with heart failure, and a patient with a small cell lung cancer. Each needs a different treatment. None of them needs a salt shaker.
If your sodium is low and nobody has assessed your volume status or checked a urine osmolality, the cause has not been established. Everything after that is guesswork.
Board-certified nephrology at Remix Medical in Houston. Call (713) 597-5131 or book online.
The causes
SIADH — inappropriate release of antidiuretic hormone, which tells the kidney to hold water. Caused by lung disease, brain injury, malignancy, and a long list of medications. The most common cause in hospitalized patients.
Medications. Thiazide diuretics above all. Also SSRIs, carbamazepine, NSAIDs, and desmopressin. This is the first thing we look at, because stopping the drug often solves it.
Heart failure, cirrhosis, and nephrotic syndrome. The body senses low effective circulation and retains water even though total body water is already excessive.
True volume depletion — vomiting, diarrhea, over-diuresis. Here saline genuinely is the treatment.
Adrenal insufficiency and hypothyroidism, both of which are found by testing and missed by not testing.
Primary polydipsia — drinking more water than the kidneys can excrete.
Beer potomania and the tea-and-toast pattern in older adults — too little solute intake to carry water out.
Correcting it too fast is dangerous
This is the part that matters most, and the reason hyponatremia belongs to nephrology.
When sodium has been low for more than two days, the brain adapts. Correcting it rapidly causes osmotic demyelination syndrome — permanent, devastating neurologic injury that appears days after the sodium has been "fixed."
The correction limit is roughly 8 mEq/L in 24 hours, less in high-risk patients: alcohol use disorder, malnutrition, liver disease, hypokalemia, sodium below 105.
Overcorrection happens easily and often accidentally. A patient whose underlying cause resolves — the thiazide is stopped, volume is repleted — will suddenly dump free water and self-correct faster than any protocol intended. Anticipating that, and being prepared to give back free water or desmopressin to slow it, is the difference between a good outcome and a catastrophe.
The correction rate matters more than the number itself.
Acute versus chronic
Sodium that falls within 48 hours — marathon runners, ecstasy use, post-operative fluid — causes brain swelling and requires urgent treatment with hypertonic saline. The brain has not adapted, so rapid correction is safe and necessary.
Sodium that has been low for weeks is a different disease with a different treatment, even at the identical number.
What we do
Establish volume status. Measure serum and urine osmolality and urine sodium — three tests that separate most of the causes. Check thyroid and cortisol. Review every medication.
Then treat the cause, and control the rate.
A low sodium is a question about water. If yours was answered with salt, or was never answered at all, it is worth answering properly.
Call (713) 597-5131 or book online.