High sodium in urine usually reflects one of three things: you’re eating a lot of salt, you’re taking a medication that forces your kidneys to flush sodium, or your body has a hormonal or kidney problem that prevents it from holding onto sodium properly. A normal 24-hour urine sodium level falls between 40 and 220 mEq per day, and roughly 93% of the sodium you eat ends up excreted in your urine. So the starting point for any evaluation is your diet, but when levels are persistently high or paired with low blood sodium, the causes get more specific.
High Salt Intake Is the Most Common Cause
Your kidneys are the body’s main sodium regulators, and they mirror what you eat. A study published in Scientific Reports that measured 24-hour urine collections found that participants excreting an average of 122 mmol of sodium per day were consuming roughly 7.7 grams of salt daily, based on the 93% excretion rate. If you eat more salt, your urine sodium goes up almost in lockstep. This is the most straightforward explanation and the one your doctor will consider first.
Processed foods, restaurant meals, cured meats, and salty snacks can easily push daily sodium intake well above recommended limits. When that happens, the kidneys simply dump the excess. This kind of elevated urine sodium isn’t dangerous on its own. It’s your body doing exactly what it should. But chronically high dietary sodium intake raises blood pressure over time, so a high urine sodium result can be a useful wake-up call about eating habits.
Diuretics and Other Medications
Diuretics are among the most common drug-related causes of high urine sodium. They work by blocking sodium reabsorption at specific points along the kidney’s filtering tubes, which forces more sodium (and water) into the urine. Loop diuretics have the strongest effect because they act on a segment of the kidney that normally reclaims about 25% of all filtered sodium. Thiazide diuretics target a different segment responsible for reabsorbing roughly 5% of filtered sodium, so their effect is milder but still clinically significant.
The method of delivery also matters. Continuous infusion of a loop diuretic can increase sodium excretion by about 30% compared with a single dose. Beyond diuretics, other medications that can raise urine sodium include certain anti-seizure drugs and some antidepressants, often because they trigger a hormonal side effect (more on that below). If your urine sodium is unexpectedly high, your doctor will want a full list of everything you’re taking, including over-the-counter drugs.
Hormonal Problems That Waste Sodium
Adrenal Insufficiency (Addison’s Disease)
Your adrenal glands produce a hormone called aldosterone, which tells the kidneys to reabsorb sodium and hold onto it. In Addison’s disease, the adrenal glands are damaged and aldosterone levels drop. Without that signal, the kidneys let sodium spill into the urine unchecked. The result is a combination of high urine sodium and dangerously low blood sodium. Blood pressure also drops because the body loses water along with the sodium. People with Addison’s disease often feel extreme fatigue, dizziness, and salt cravings, all of which trace back to this sodium leak.
SIADH
The syndrome of inappropriate antidiuretic hormone, or SIADH, works through a different mechanism. Here the problem isn’t too little aldosterone but too much of another hormone, ADH, which tells the kidneys to hold onto water. When ADH levels stay elevated inappropriately, the body retains excess water, diluting blood sodium levels. In response, the kidneys try to compensate by excreting more sodium. Urine sodium in SIADH is typically above 40 mEq/L. SIADH can be triggered by lung diseases, brain injuries, certain cancers, and several medications. It’s one of the most common causes of low blood sodium in hospitalized patients, and the high urine sodium is a key clue that helps distinguish it from other causes of low blood sodium.
Kidney Diseases That Cause Salt Wasting
Some kidney conditions directly impair the organ’s ability to reclaim sodium from filtered fluid. This is sometimes called salt-losing nephropathy. The kidneys filter a massive volume of sodium every day, and more than 99% of it normally gets reabsorbed. When kidney tissue is damaged by chronic inflammation, structural disease, or scarring, that reabsorption fails and sodium pours into the urine.
Cerebral salt wasting syndrome is a related condition, first described in 1950, where intracranial disease (such as a brain hemorrhage or tumor) somehow signals the kidneys to dump sodium. It looks similar to SIADH on lab tests, and distinguishing the two can be tricky, but the treatment approach differs significantly. In cerebral salt wasting, the body is genuinely volume-depleted, whereas in SIADH it is not.
Inherited Genetic Conditions
Two rare inherited conditions, Bartter syndrome and Gitelman syndrome, cause the kidneys to waste sodium from birth. Both involve defects in the proteins that transport sodium, potassium, and chloride back into the bloodstream from the kidney’s filtering tubes.
Bartter syndrome affects the part of the kidney where loop diuretics act, and it essentially mimics being on a loop diuretic permanently. The most severe forms (types I and II) appear before or shortly after birth and cause major salt and water losses, often with excessive urination. Gitelman syndrome affects a different, downstream segment, the same one targeted by thiazide diuretics. It’s more common, with an estimated prevalence of about 1 in 40,000 people, and tends to be milder. People with Gitelman syndrome often aren’t diagnosed until adolescence or adulthood, when blood work reveals low potassium, low magnesium, and persistently elevated urine sodium.
Both conditions are autosomal recessive, meaning you need to inherit a defective gene copy from each parent. They’re managed with electrolyte supplements and sometimes medications that counteract the sodium loss, but they require lifelong monitoring.
How Doctors Interpret Urine Sodium Results
A single urine sodium measurement doesn’t tell the full story. Doctors typically look at it alongside blood sodium levels, kidney function, and your medication list. One key calculation is the fractional excretion of sodium, or FENa, which compares how much sodium your kidneys filter with how much actually ends up in the urine. A FENa below 1% suggests the kidneys are aggressively holding onto sodium, which happens when blood flow to the kidneys is reduced (from dehydration, for example). A FENa above 1% suggests the kidney tubes themselves are damaged or being overridden by a drug or hormone.
This test has been used since 1976, though it has real limitations. It works best in people who are already showing signs of kidney stress and can be thrown off by diuretics. It’s a screening tool, not a definitive answer. Your doctor may also order a full 24-hour urine collection rather than relying on a single random sample, since sodium excretion fluctuates throughout the day based on meals, hydration, and activity.
What a High Result Means for You
If your urine sodium came back elevated on routine testing, the first question to ask yourself is whether it reflects what you’re eating. A 24-hour urine sodium test is actually one of the most reliable ways to estimate true daily salt intake, and most people underestimate how much sodium they consume. If your blood sodium is normal and you’re not on diuretics, dietary salt is the most likely explanation.
If your blood sodium is low at the same time, the picture changes. That combination points toward one of the conditions described above: adrenal insufficiency, SIADH, cerebral salt wasting, or a kidney disorder. Your doctor will likely check hormone levels, kidney function, and possibly imaging depending on the clinical picture. For people with unexplained chronic sodium wasting, especially those diagnosed young, genetic testing for Bartter or Gitelman syndrome may be warranted.