Sodium (Na) Test: Normal Levels, High/Low Causes

What Is a Sodium (Na) Blood Test?

Sodium is the most abundant positively charged electrolyte in the fluid outside your cells. It plays a critical role in maintaining water balance, nerve function, and muscle contraction. When I see patients in my clinic, I often order a sodium level as part of a basic metabolic panel — it gives me a quick snapshot of hydration status and how the kidneys are working.

Why Is Sodium Measured?

Doctors check sodium to evaluate fluid and electrolyte balance, especially if you have symptoms like confusion, fatigue, muscle cramps, or seizures. It’s also used to monitor conditions such as heart failure, kidney disease, liver cirrhosis, and adrenal disorders.

Normal Sodium Levels by Age and Gender

Note: Reference ranges can vary slightly between laboratories. Always interpret results with your own lab’s normal values.

Low Sodium (Hyponatremia) — Causes and Symptoms

Hyponatremia (Na < 135 mmol/L) is one of the most common electrolyte disorders I encounter. Symptoms range from mild nausea and headache to severe confusion, seizures, and coma. Common causes include:

• Excessive water intake (e.g., marathon runners)
• Diuretic use (water pills)
• Kidney or heart failure
• Liver cirrhosis or ascites
• Addison’s disease (adrenal insufficiency)
• Syndrome of inappropriate antidiuretic hormone (SIADH)

What should I do if my sodium is low?

If you have mild symptoms, your doctor may recommend reducing fluid intake and adjusting medications. Severe hyponatremia requires careful hospital correction because raising sodium too quickly can cause permanent brain damage.

High Sodium (Hypernatremia) — Causes and Symptoms

Hypernatremia (Na > 145 mmol/L) often means you are dehydrated — your body has too little water relative to sodium. Symptoms include intense thirst, dry mouth, confusion, restlessness, and muscle twitching. Causes include:

• Inadequate water intake (common in elderly or bedridden patients)
• Excessive sweating, fever, or burns
• Diabetes insipidus
• High-sodium intravenous fluids or dietary salt overload
• Certain medications (e.g., lithium, corticosteroids)

How is high sodium treated?

Treatment focuses on safely replacing water, usually with intravenous fluids or encouraged oral intake. The underlying cause — such as managing diabetes insipidus — must also be addressed.

Can Diet Alone Cause Abnormal Sodium Levels?

In my experience, a normal diet rarely leads to dangerously high sodium in people with healthy kidneys. However, consuming large amounts of salty food combined with low water intake can raise sodium. Conversely, a low-sodium diet is seldom the sole cause of hyponatremia unless combined with heavy water drinking or a medical condition.

Sodium During Pregnancy

During pregnancy, blood sodium levels tend to stay within the normal range, though mild dilutional hyponatremia can occur due to increased blood volume. Severe fluctuations warrant investigation for conditions such as preeclampsia or hyperemesis gravidarum.

How to Prepare for a Sodium Blood Test

No special preparation is needed. You can eat and drink normally unless your doctor tells you otherwise. Some medications (e.g., diuretics, antidepressants) affect sodium, so bring a list of your current medicines.

When to Call Your Doctor

If you experience confusion, severe headache, vomiting, muscle weakness, or rapid changes in thirst and urination, see a healthcare professional promptly. A single abnormal sodium result doesn’t mean a disease — many factors can temporarily shift levels.