Sodium (Na) Blood Test: Normal Range, High & Low

Sodium (Na) is an electrolyte that helps control fluid balance, nerve signals, and muscle function. A blood sodium test is often part of a basic or comprehensive metabolic panel. Results outside the normal range may indicate dehydration, kidney issues, or other conditions and should be discussed with a clinician.

Sodium is the main electrolyte found outside cells in the blood and tissue fluid. It comes primarily from dietary salt and is absorbed in the digestive tract. The body carefully controls sodium levels through the kidneys, which filter blood and adjust how much sodium is excreted in urine or reabsorbed based on hydration and dietary intake. Sodium works together with potassium to maintain the electrical charges that nerve cells and muscles need to function properly. It also plays a central role in regulating blood volume and blood pressure by influencing how much water the body retains. A blood sodium test measures the concentration of this electrolyte in the bloodstream at a single point in time.

A sodium blood test is commonly ordered as part of routine bloodwork, particularly within a basic metabolic panel (BMP) or comprehensive metabolic panel (CMP), and it may also appear in a dedicated electrolyte panel. Clinicians often check sodium levels when someone has symptoms such as confusion, weakness, nausea, or unusual thirst, or when monitoring conditions that affect fluid balance like kidney disease, heart failure, or hormone disorders. It can also help evaluate the effects of certain medications, including diuretics, or track recovery after significant fluid loss from vomiting, diarrhea, or heavy sweating. Because sodium levels reflect overall fluid and electrolyte balance, this test is often reviewed together with other markers on the same panel, such as potassium and magnesium.

Sodium results are typically reported in mmol/L, and adult reference ranges are generally similar in mEq/L. The exact normal range can vary slightly between laboratories depending on the equipment and methods used, so it helps to check the reference range printed directly on your lab report.

Elevated sodium levels, known as hypernatremia, most often reflect a relative lack of water compared to sodium in the body rather than too much salt intake alone. Common contributors include not drinking enough fluids, especially in older adults or people with limited mobility, as well as fluid losses from prolonged vomiting, diarrhea, excessive sweating, or fever. Certain medical conditions that affect the body's ability to concentrate urine, such as diabetes insipidus, can also lead to higher sodium readings because the kidneys are unable to conserve water appropriately. Some medications, including certain diuretics and corticosteroids, may contribute to elevated levels as well. In hospital settings, receiving large amounts of intravenous fluids containing sodium can also raise levels. Because high sodium often develops gradually and can be linked to underlying fluid balance problems, a single elevated reading is not enough to identify the cause. A healthcare provider will typically consider hydration status, other electrolyte results such as potassium, kidney function markers like blood urea nitrogen, and any symptoms such as confusion, restlessness, or excessive thirst before determining next steps. Very high sodium levels can be serious and may need prompt medical evaluation.

Low sodium levels, called hyponatremia, are a common electrolyte finding and can have many possible explanations. Excess water intake relative to sodium, such as drinking very large amounts of fluid in a short time, can dilute sodium concentration in the blood. Certain medications, particularly some diuretics and antidepressants, are frequently linked to lower sodium readings. Conditions that affect the kidneys, liver, heart, or hormone-producing glands can also alter how the body manages sodium and water, contributing to lower levels. Significant fluid loss from vomiting, diarrhea, or heavy sweating combined with plain water replacement instead of electrolyte solutions may also play a role. In some cases, hormonal imbalances involving antidiuretic hormone can cause the body to retain too much water relative to sodium. Because hyponatremia can range from mild to severe, and because symptoms like confusion, headache, or muscle cramps can sometimes overlap with other conditions, any low sodium result should be reviewed by a healthcare provider, especially if it is marked as significantly below the normal range.

Sodium is usually interpreted alongside other electrolytes rather than on its own. Potassium, calcium, and magnesium levels are often checked together because they all influence nerve and muscle function and can shift together during illness or dehydration. Kidney function markers such as blood urea nitrogen can also provide context, since the kidneys play a central role in regulating sodium balance. Diet, hydration habits, exercise, and certain medications, including diuretics, hormone therapies, and some psychiatric medications, can all influence sodium readings. Because testing methods and reference ranges can differ somewhat between laboratories, it is helpful to compare results using the range listed on the specific lab report rather than relying solely on general reference values found online.

If your sodium result falls outside the normal range, a healthcare provider can help interpret it alongside your symptoms, medications, and other lab values. It may help to mention recent fluid intake, illnesses involving vomiting or diarrhea, and any new medications when discussing results. Seek urgent care if you experience severe confusion, seizures, extreme weakness, or significant changes in alertness alongside an abnormal sodium result, since these can sometimes signal a more serious imbalance. Uploading a lab report to MediWing can help you get a plain-language explanation of your sodium result and see how it changes over time alongside related markers.