A normal blood sodium level falls between 135 and 145 milliequivalents per liter (mEq/L). This is the standard reference range used across age groups, including older adults. Sodium is one of the most tightly regulated substances in your body, and even small shifts outside that window can cause noticeable symptoms.
What the Numbers Mean
Sodium helps regulate fluid balance, nerve signaling, and muscle function. Your kidneys do most of the work keeping it in range, adjusting how much sodium you retain or excrete based on what your body needs at any given moment. When that system works well, your level stays remarkably stable.
A result below 135 mEq/L is called hyponatremia (low sodium). A result above 145 mEq/L is called hypernatremia (high sodium). Both conditions are graded by severity:
- Mild low sodium: 130 to 134 mEq/L
- Moderate low sodium: 120 to 129 mEq/L
- Severe low sodium: below 120 mEq/L
- Mild high sodium: 145 to 150 mEq/L
- Moderate high sodium: 151 to 155 mEq/L
- Severe high sodium: above 155 mEq/L
Hospitals flag sodium below 125 mEq/L as a critical value requiring intervention within about an hour. Sodium above 150 mEq/L is also flagged, though the response window is slightly wider, generally six to eight hours.
How Low Sodium Feels
Low sodium is more common than high sodium, and it often develops gradually enough that people don’t connect their symptoms to a blood chemistry problem. Brain cells are especially sensitive to the fluid shifts that happen when sodium drops, which is why most symptoms are neurological.
At mildly low levels, you might notice fatigue, headaches, nausea, or a general loss of appetite. These are easy to dismiss as dehydration or a bad night of sleep. As levels fall further into the moderate range, confusion, irritability, muscle cramps, and vomiting become more common. Severe hyponatremia, below 120 mEq/L, can cause seizures, loss of consciousness, and in rare cases, death. People who are premenopausal appear to be at the greatest risk of brain damage from acute drops in sodium.
The speed of the drop matters as much as the number itself. A slow decline to 125 mEq/L over several days may cause mild confusion, while a rapid drop to the same level can trigger a medical emergency because the brain doesn’t have time to adapt to the fluid changes.
Common Causes of Imbalance
Low sodium often comes down to too much water relative to sodium in the body. This can happen from drinking excessive amounts of water (common during endurance exercise), chronic conditions affecting the kidneys, liver, or heart, or hormonal imbalances that disrupt how your body manages fluid. Certain medications, particularly water pills used for blood pressure, are among the most frequent culprits. Persistent vomiting or diarrhea can also push levels down.
High sodium typically results from not drinking enough water, significant fluid loss through fever, burns, or heavy sweating, or conditions that impair your ability to feel thirst. Older adults are particularly vulnerable to high sodium because thirst signals weaken with age and kidney function gradually declines.
Who Is Most at Risk
Older adults face a higher risk of both low and high sodium. The physiological changes that come with aging, including reduced kidney efficiency and changes in hormone regulation, make it harder for the body to maintain balance. This doesn’t mean the “normal” range changes with age; a reading of 132 mEq/L is still considered low whether you’re 35 or 75. But the likelihood of landing outside the range increases.
Endurance athletes, people on certain blood pressure medications, those with chronic kidney disease, and anyone recovering from surgery or illness involving fluid loss should be especially aware of sodium balance.
How Sodium Is Tested
Sodium is measured through a standard blood draw, most commonly as part of a basic metabolic panel (sometimes called an electrolyte panel). This panel measures eight substances in your blood, including sodium, potassium, chloride, and carbon dioxide. A comprehensive metabolic panel includes those same eight tests plus six additional ones focused on liver and kidney function.
You may need to fast for eight hours before the test, depending on what else is being measured alongside sodium. The blood draw itself takes a few minutes, and results are typically available the same day or the next. If your doctor orders routine bloodwork during an annual physical, sodium is almost certainly included.
Dietary Sodium vs. Blood Sodium
It’s worth understanding that the sodium level in your blood and the amount of sodium you eat are related but not the same thing. Your kidneys are remarkably good at filtering out excess dietary sodium in healthy people, so eating a salty meal won’t immediately spike your blood sodium level. The body compensates by triggering thirst so you drink more water, which dilutes the extra sodium.
That said, chronically high sodium intake strains this system over time and contributes to high blood pressure, heart disease, and kidney damage. The FDA and the Dietary Guidelines for Americans recommend limiting dietary sodium to less than 2,300 milligrams per day. Most Americans consume significantly more than that, largely from processed and restaurant foods rather than the salt shaker.
Reducing dietary sodium won’t necessarily change your blood sodium reading on a lab test, but it protects the cardiovascular and kidney systems that keep your blood sodium stable in the first place.