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Sodium Blood Test
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Lab Tests

Sodium Blood Test

A sodium blood test measures the levels of this essential electrolyte to help monitor fluid balance, kidney function, and overall health.

What is a sodium blood test?

A sodium blood test measures the amount of sodium in your blood. Sodium is a type of electrolyte—a mineral that carries an electrical charge when dissolved in body fluids. Electrolytes are found in your blood, urine, tissues, and other fluids, where they help control fluid levels and maintain the body's acid-base (pH) balance. Sodium also plays a critical role in ensuring your nerves and muscles function properly.

Most of the sodium in your body comes from your diet. Your kidneys regulate these levels by removing excess sodium through your urine. Because your body maintains sodium within a very narrow range, levels that are too high or too low may indicate dehydration, kidney problems, or other medical conditions.

What is it used for?

This is a routine test used to check your general health and monitor conditions affecting your body's balance of fluids, electrolytes, and acidity. It is frequently performed as part of an electrolyte panel, a basic metabolic panel (BMP), or a comprehensive metabolic panel (CMP).

Why do I need a sodium blood test?

Your provider may order this test during a routine checkup, if you take medications that affect fluid balance, or if you exhibit symptoms of abnormal sodium levels.

Symptoms of high sodium (hypernatremia)

  • Thirst
  • Urinating very little
  • Vomiting
  • Diarrhea
  • Confusion
  • Muscle twitching
  • Seizures

Without treatment, extremely high sodium levels can lead to a coma and become life-threatening.

Symptoms of low sodium (hyponatremia)

  • Weakness
  • Fatigue
  • Confusion
  • Muscle twitching
  • Seizures

Without treatment, extremely low sodium levels can also lead to a coma and become life-threatening.

What happens during a sodium blood test?

A health care professional will collect a blood sample from a vein in your arm using a small needle. The procedure typically takes less than five minutes, and you may feel a brief sting during the process.

Preparation and Risks

Your provider will inform you if you need to fast or stop taking certain medications before the test. Do not stop taking any prescribed medicines unless instructed to do so. The risks are minimal, typically limited to slight pain or bruising at the needle site.

What do the results mean?

Because abnormal sodium levels can stem from many different conditions, providers usually interpret these results alongside other electrolyte measurements.

Higher than normal results

High sodium may indicate:

  • Dehydration (due to insufficient fluid intake, diarrhea, or diuretic use)
  • Adrenal gland disorders
  • Kidney disease
  • Diabetes insipidus

Lower than normal results

Low sodium may indicate:

  • Sodium loss from vomiting or diarrhea
  • Conditions causing fluid retention (which dilutes sodium), such as kidney disease, cirrhosis, heart failure, certain brain/lung diseases, or cancer
  • Use of certain medications, including some antidepressants and over-the-counter pain relievers
  • Addison disease
  • Malnutrition

Note that results outside the normal range do not always indicate a medical condition requiring treatment, as age, sex, and medications can influence levels.

Additional Information

Sodium levels are often evaluated alongside an anion gap test, which measures the difference between negatively and positively charged electrolytes to check for acid imbalances.

Frequently Asked Questions

Symptoms such as unexplained confusion, seizures, extreme thirst, or sudden changes in urine output, especially in patients with kidney disease, heart failure, or those on diuretics, are common triggers. Routine labs often include sodium as part of an electrolyte panel.
For hypernatremia, gradual rehydration with hypotonic fluids (e.g., 0.45% saline) is used to lower sodium slowly, avoiding rapid shifts that risk cerebral edema. For hyponatremia, treatment depends on severity: mild cases may involve fluid restriction or isotonic saline, while severe or symptomatic cases often require hypertonic saline (3%) under close monitoring to raise sodium safely.
Severe dehydration typically raises sodium (hypernatremia) because water loss outpaces sodium loss. However, if dehydration is accompanied by vomiting or diarrhea, sodium can be lost, potentially leading to hyponatremia if fluid replacement is inadequate.
Generally, no special restrictions are needed. However, if you are on a low‑sodium diet or taking medications that affect fluid balance (e.g., diuretics, ACE inhibitors), inform your provider, as these can influence the result. No fasting is required unless your clinician specifies otherwise.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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