Serum Sodium Test – Indications, Procedures, Results

Last updated: February 8, 2026Reviewed date: February 8, 2026Reading time: 8 min read
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A sodium blood test is a routine test that allows your doctor to see how much sodium is in your blood. It's also called a serum sodium test. Sodium is an essential mineral to your body. It's also referred to as Na+. When sodium levels in...

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Article Summary

A sodium blood test is a routine test that allows your doctor to see how much sodium is in your blood. It's also called a serum sodium test. Sodium is an essential mineral to your body. It's also referred to as Na+. When sodium levels in the blood become too low, it leads to hyponatremia, causing symptoms that include lethargy, confusion, and fatigue. Hyponatremia is the most...

Key Takeaways

  • This article explains How the Test is Performed in simple medical language.
  • This article explains How to Prepare for the Test in simple medical language.
  • This article explains How the Test will Feel in simple medical language.
  • This article explains Why the Test is Performed in simple medical language.
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These warning signs are general safety guidance. Local emergency numbers and clinical judgment should always come first.

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Use this article to understand possible causes, tests, treatment options, prevention, and questions to ask your clinician.

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A sodium blood test is a routine test that allows your doctor to see how much sodium is in your blood. It’s also called a serum sodium test. Sodium is an essential mineral to your body. It’s also referred to as Na+.

When sodium levels in the blood become too low, it leads to hyponatremia, causing symptoms that include lethargy, confusion, and fatigue. Hyponatremia is the most common electrolyte disorder — research suggests that approximately 1.7% of people in the United States have the condition.

The sodium blood test measures the amount of sodium in the blood or sodium can also be measured using a urine test.

How the Test is Performed

A blood sample is needed.

How to Prepare for the Test

Your health care provider may tell you to temporarily stop taking medicines that may affect the test. These include:

  • Antibiotics
  • Antidepressants
  • Some high blood pressure medicines
  • Lithium
  • Nonsteroidal infection, or irritation, often causing pain, swelling, heat, or redness. সহজ বাংলা: শরীরের প্রদাহ; ব্যথা, ফোলা বা লালভাব হতে পারে।" data-rx-term="inflammation" data-rx-definition="Inflammation is the body’s response to injury, infection, or irritation, often causing pain, swelling, heat, or redness. সহজ বাংলা: শরীরের প্রদাহ; ব্যথা, ফোলা বা লালভাব হতে পারে।">inflammation, pain, or swelling. সহজ বাংলা: প্রদাহ/ফোলা/ব্যথা কমায়।" data-rx-term="anti-inflammatory" data-rx-definition="Anti-inflammatory means reducing inflammation, pain, or swelling. সহজ বাংলা: প্রদাহ/ফোলা/ব্যথা কমায়।">anti-inflammatory drugs (NSAIDs)
  • Water pills (diuretics)

DO NOT stop taking any medicine before talking to your provider.

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.

Why the Test is Performed

Sodium is a substance that the body needs to work properly. Sodium is found in most foods. The most common form of sodium is sodium chloride, which is table salt.

This test is usually done as part of an electrolyte or basic metabolic panel blood test .

Your blood sodium level represents a balance between the sodium and water in the food and drinks you consume and the amount in your urine. A small amount is lost through stool and sweat.

Many things can affect this balance. Your provider may order this test if you:

  • Have had a recent injury, surgery, or serious illness
  • Consume large or small amounts of salt or fluid
  • Receive intravenous (IV) fluids
  • Take diuretics (water pills) or certain other medicines, including the hormone aldosterone

Normal Results

The normal range for blood sodium levels is 135 to 145 mEq/L.

Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your provider about the meaning of your specific test results.

What Abnormal Results Mean

An abnormal sodium level can be due to many different conditions.

Higher than normal sodium level is called hypernatremia. It may be due to:

  • Increased fluid loss due to excessive sweating, diarrhea, burns, or use of diuretics
  • Adrenal gland problems such as Cushing syndrome or hyperaldosteronism
  • insulin is low or not working well. সহজ বাংলা: রক্তে চিনি বেশি থাকার রোগ।" data-rx-term="diabetes" data-rx-definition="Diabetes is a condition where blood sugar stays too high because insulin is low or not working well. সহজ বাংলা: রক্তে চিনি বেশি থাকার রোগ।">Diabetes insipidus (type of diabetes in which kidneys are not able to conserve water)
  • Too much salt or sodium bicarbonate in the diet
  • Use of certain medicines, including corticosteroids, laxatives, lithium, and medicines such as ibuprofen or naproxen

Lower than normal sodium level is called hyponatremia. It may be due to:

  • Use of medicines such as diuretics (water pills), morphine, and selective serotonin reuptake inhibitor (SSRI) antidepressants
  • Increased fluid loss from body, vomiting, or diarrhea
  • An increase in total body water is seen in those with heart failure, certain kidney diseases, or cirrhosis of the liver
  • Adrenal glands not making enough of their hormones ( Addison disease )
  • Buildup in the urine of waste product from the fat breakdown (ketonuria)
  • Syndrome of inappropriate antidiuretic hormone secretion (the antidiuretic hormone is released from an abnormal place in the body)
  • Too much of the hormone vasopressin

Risks

There is very little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

  • Excessive bleeding
  • Fainting or feeling lightheaded
  • Hematoma (blood accumulating under the skin)
  • Infection (a slight risk any time the skin is broken)

FAQ

What happens if serum sodium is low?

  • When sodium levels in the blood become too low, it leads to hyponatremia, causing symptoms that include lethargy, confusion, and fatigue. Hyponatremia is the most common electrolyte disorder — research suggests that approximately 1.7% of people in the United States have the condition.

Why is a serum sodium test done?

  • Why do I need a sodium blood test? Your health care provider may have ordered a sodium blood test as part of your regular checkup or if you have symptoms of too much sodium (hypernatremia) or too little sodium (hyponatremia) in your blood. Symptoms of high sodium levels (hypernatremia) include Excess thirst.

What happens if serum sodium is high?

  • Hypernatremia typically causes thirst. The most serious symptoms of hypernatremia result from brain dysfunction. Severe hypernatremia can lead to confusion, muscle twitching, seizures, coma, and death.

What does the positive sodium test mean?

  • High sodium levels in the urine could indicate the use of water pills. Too much salt in your diet. Low function of the adrenal glands, which are in your kidneys. infection, or irritation, often causing pain, swelling, heat, or redness. সহজ বাংলা: শরীরের প্রদাহ; ব্যথা, ফোলা বা লালভাব হতে পারে।" data-rx-term="inflammation" data-rx-definition="Inflammation is the body’s response to injury, infection, or irritation, often causing pain, swelling, heat, or redness. সহজ বাংলা: শরীরের প্রদাহ; ব্যথা, ফোলা বা লালভাব হতে পারে।">Inflammation of your kidneys.

How do you increase serum sodium?

  • Intravenous (IV) fluids with a high concentration of sodium, and/or diuretics to raise your blood sodium levels. Loop Diuretics – also known as “water pills” as they work to raise blood sodium levels, by making you urinate out extra fluid.

What causes sodium deficiency?

  • Chronic, severe vomiting or diarrhea and other causes of dehydration. This causes your body to lose electrolytes, such as sodium and also increases ADH levels. Drinking too much water. Drinking excessive amounts of water can cause low sodium by overwhelming the kidneys’ ability to excrete water.

What are the symptoms of high sodium levels?

Symptoms of Hypernatremia
  • Muscle weakness.
  • Restlessness.
  • Extreme thirst.
  • Confusion.
  • Lethargy.
  • Irritability.
  • Seizures.
  • Unconsciousness.

What does low sodium indicate?

  • In hyponatremia, the level of sodium in the blood is too low. A low sodium level has many causes, including consumption of too many fluids, kidney failure, heart failure, cirrhosis, and use of diuretics. Symptoms result from brain dysfunction.

What is a critical sodium level?

  • In many hospital laboratories, 160 mEq/L is chosen as the upper critical value. The evidence of this study suggests that sodium in the range of 155-160 mEq/L is associated with a high risk of death and that 155 mEq/L rather than 160 mEq/L might be more suitable as the upper critical level.

What are the 3 causes of hypernatremia?

  • Common causes include diuretic use, diarrhea, heart failure, liver… read more ). Patients with renal disease can also be predisposed to hypernatremia when their kidneys are unable to maximally concentrate urine.

Why would sodium be high?

  • Certain conditions may cause an excess of sodium in the blood. Specific causes of hypernatremia include Dehydration or a loss of body fluids from prolonged vomiting, diarrhea, sweating, or high fevers. Dehydration from not drinking enough water.

How do you fix low sodium?

Treatment for hyponatremia
  • cutting back on fluid intake.
  • adjusting the dosage of diuretics.
  • taking medications for symptoms such as headaches, nausea, and seizures.
  • treating underlying conditions.
  • stopping or changing a medication for a chronic condition that may be negatively affecting blood sodium.

Can a person recover from low sodium levels?

  • Hyponatremia can result from multiple diseases that often are affecting the lungs, liver or brain, heart problems like congestive heart failure, or medications. Most people recover fully with their doctor’s help.

What does low sodium do to the brain?

  • When the sodium in your blood falls below 135, a condition known as hyponatremia occurs, which can lead to numerous complications, ranging from loss of energy, confusion, muscle weakness, and nausea to more serious issues such as seizures, coma, and even death.

Which fruit has high sodium?

  • The fruit containing the highest sodium content is Mammy apple, a tropical fruit. One fruit or about 850 gm of mammy apple contains about 127 mg of sodium. Apple skin, guavas, and passion fruits contain about 50 mg of sodium per serving. About 130 gm of honeydew melon approximately contains 30 mg of sodium.

What foods raise sodium levels?

High-Sodium Foods
  • Smoked, cured, salted, or canned meat, fish, or poultry including bacon, cold cuts, ham, frankfurters, sausage, sardines, caviar and anchovies.
  • Frozen breaded meats and dinners, such as burritos and pizza.
  • Canned entrees, such as ravioli, spam, and chili.
  • Salted nuts.
  • Beans canned with salt added.

What foods increase sodium levels?

Top Sources of Sodium
  • Bread and rolls.
  • Pizza.
  • Sandwiches.
  • Cold cuts and cured meats.
  • Soups.
  • Burritos and tacos.
  • Savory snacks*
  • Chicken.

How long does it take for sodium levels to return to normal?

  • The medical team will restore the sodium level over the course of several hours or days, depending on the severity of your condition. A too-rapid infusion of sodium can lead to osmotic demyelination syndrome (ODS), a form of brain damage.

What is the normal range of serum sodium?

  • The normal range for blood sodium levels is 135 to 145 milliequivalents per liter (mEq/L).

What does a sodium level of 126 mean?

  • A: The normal level of sodium in the blood is between 135 mEq/L (milliequivalents per liter) and 145 mEq/L. A level below 135 is low. Doctors call it hyponatremia. In general, a sodium level of 130 mEq/L or higher is not dangerous unless there has been a recent rapid fall from a normal blood level.

What does a sodium level of 115 mean?

  • Severe hyponatremia (serum/plasma sodium <115 mmol/L), particularly of rapid onset, is associated with marked confusion, seizures, and coma; without emergent treatment, severe hyponatremia can be fatal.

What is the difference between hypernatremia and hyponatremia?

  • In hyponatremia, an excess of water in the body can lead to a low concentration of sodium in the blood, he said. And in hypernatremia, a deficit of water in the body can lead to a high concentration of sodium in the blood.
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Which doctor may help?

Start with a registered doctor or the nearest qualified health center.

What to tell the doctor

  • Write when the problem started and how it changed.
  • Bring old prescriptions, investigation reports, and current medicines.
  • Write allergies, pregnancy status, diabetes, kidney/liver disease, and major past illnesses.
  • Bring one family member if the patient is weak, elderly, confused, or a child.

Questions to ask

  • What is the most likely cause of my symptoms?
  • Which danger signs mean I should go to hospital quickly?
  • Which tests are necessary now, and which can wait?
  • How should I take medicines safely and what side effects should I watch for?
  • When should I come for follow-up?

Tests to discuss

  • Vital signs: temperature, pulse, blood pressure, oxygen saturation
  • Basic physical examination by a clinician
  • CBC, urine test, blood sugar, or imaging only when clinically needed

Avoid these mistakes

  • Do not use antibiotics, steroid tablets/injections, or strong painkillers without proper medical advice.
  • Do not hide pregnancy, kidney disease, ulcer, allergy, or blood thinner use.
  • Do not delay emergency care when danger signs are present.

Medicine safety and first-aid guide

This section is for patient education only. It does not replace a doctor, pharmacist, or emergency care.

Safe first steps

  • Drink safe fluids and monitor temperature.
  • In dengue-prone areas, discuss CBC and platelet count when fever persists or warning signs appear.
  • Use tepid sponging for high fever discomfort; avoid ice-cold bathing.

OTC medicine safety

  • For fever, common fever medicine may be discussed with a clinician or pharmacist.
  • Avoid aspirin/ibuprofen-like medicines in suspected dengue unless a doctor says it is safe.

Avoid these mistakes

  • Do not start antibiotics without a proper medical decision.
  • Do not use steroid tablets or injections casually for quick relief.
  • Do not delay emergency care because of home remedies.

Get urgent help if

  • Fever with breathing difficulty, confusion, repeated vomiting, bleeding, severe weakness, stiff neck, or dehydration needs urgent care.
Medicine names, dose, and timing must be decided by a qualified clinician or pharmacist after checking age, pregnancy, allergy, other diseases, and current medicines.

For rural patients and family caregivers

Patient health record and symptom diary

Write your symptoms, medicines already taken, test results, and questions before visiting a doctor. This note stays on your device unless you print or copy it.

Doctor to discuss: Medicine doctor / pediatrician for children / qualified clinician
Tests to discuss with doctor
  • Temperature chart and hydration assessment
  • CBC with platelet count if fever persists or dengue/other infection is possible
  • Urine test, malaria/dengue tests, chest evaluation, or blood culture only when clinically indicated
Questions to ask
  • What is the most likely cause of my symptoms?
  • Which warning signs mean I should go to emergency care?
  • Which tests are really needed now?
  • Which medicines are safe for my age, pregnancy status, allergy, kidney/liver/stomach condition, and current medicines?
  • Do I need antibiotics, or is this more likely viral?

Emergency warning signs such as chest pain, severe breathing difficulty, sudden weakness, confusion, severe dehydration, major injury, or loss of bladder/bowel control need urgent medical care. Do not wait for online information.

Safe pathway to proper treatment

Care roadmap for: Serum Sodium Test – Indications, Procedures, Results

Use this simple roadmap to understand the next safe steps. It is educational and does not replace examination by a doctor.

Go to emergency care if you notice:
  • Severe or rapidly worsening symptoms
  • Breathing difficulty, chest pain, fainting, confusion, severe weakness, major injury, or severe dehydration
Doctor / service to discuss: Qualified healthcare provider; specialist depends on symptoms and examination.
  1. Step 1

    Check danger signs first

    If danger signs are present, seek emergency care and do not wait for online information.

  2. Step 2

    Record the symptom story

    Write when symptoms started, severity, medicines already taken, allergies, pregnancy status, and test results.

  3. Step 3

    Visit a qualified clinician

    A doctor, nurse, or qualified healthcare provider can examine you and decide which tests or treatment are needed.

  4. Step 4

    Do only useful tests

    Do tests after clinical assessment. Avoid unnecessary tests, random antibiotics, or repeated medicines without diagnosis.

  5. Step 5

    Follow up and return early if worse

    If symptoms worsen, new warning signs appear, or treatment is not helping, return for review quickly.

Rural patient practical tips
  • Take a written symptom diary and all previous prescriptions/test reports.
  • Do not hide medicines already taken, even herbal or over-the-counter medicines.
  • Ask which warning signs mean urgent referral to hospital.

This roadmap is for education. A real diagnosis and treatment plan requires history, examination, and clinical judgment.

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Write your symptom story. A health professional or site editor can review it before any answer is prepared. This box is not for emergency care.

Emergency first: Severe chest pain, breathing trouble, unconsciousness, stroke signs, severe injury, heavy bleeding, or rapidly worsening symptoms need urgent local medical care now.

Frequently Asked Questions

Is this article a replacement for a doctor?

No. It is educational content only. Patients should consult a qualified clinician for diagnosis and treatment.

When should I seek urgent care?

Seek urgent care for severe symptoms, rapidly worsening condition, breathing difficulty, severe pain, neurological changes, or any emergency warning sign.

References

Add references, clinical guidelines, textbooks, journal articles, or trusted medical sources here. You can edit this area from the RX Article Professional Blocks panel.

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