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What Is Serum Sodium Test?

Sodium (Na) is one of the essential minerals of our body. Sodium is most commonly consumed in the form of table salt, and it is also found in most of our dietary products. Our body requires sodium for maintaining fluid content in the body and for the proper functioning of nerves and muscles.

Sodium is an electrolyte which means it is a charged ion. Due to this property, it helps generate electrical signals in nerves and muscles and thus brings about muscles and maintains brain activity. Moreover, it also holds water inside our body and prevents losing excess water through the kidney, keeping our body fluid balanced.

It is a major cation (positively charged ion) present in the body's extracellular fluid (blood). Excess sodium is excreted through urine, feces, and sweats. The body maintains an adequate amount and concentration of sodium through various mechanisms, including thirst and certain hormones for optimal body functioning.

Blood sodium levels are tested to look for any imbalance in its concentration, which could indicate the underlying abnormality. It may be tested as part of Basic Metabolic Penal, a group of related tests including calcium, bicarbonate, chloride, creatinine, glucose, potassium, and blood urea nitrogen levels. Also, it is a component of Electrolyte Penal where potassium, bicarbonate, and chloride are the other electrolytes tested.

What Is The Test Used For?

The test is used to check the amount of sodium in your body. An adequate amount is necessary to keep up with the normal functioning of your body; any derangement in its levels may indicate some impairment in your body. Therefore, this test assists in uncovering the causes of electrolyte imbalance.

Your body maintains sodium in a narrow range of 135-145mEq/L; an increase in sodium concentration above this level is called hypernatremia, and a decrease is called hyponatremia. Both conditions have different causes and different signs and symptoms.


Elevation of sodium content above 145mEq/L in your blood may lead to:

  • Thirst
  • Fatigue and weakness
  • Insomnia (loss of sleep)
  • Swelling in hands and feet
  • Rapid and irregular heartbeat
  • Hypertension (raised blood pressure)

This condition can affect people of any age group, but elders, infants, and bedridden patients should be closely monitored. A lot of causes bring about hypernatremia, including:

  • Dehydration due to decrease water intake or loss of excess water through diarrhea or sweating.
  • Drinking too much salty water or consuming too much salt.
  • Low level of Anti-diuretic hormones (ADH) or Vasopressin, which losses excess amount of water from the body through the kidney, leading to severe dehydration. This condition is called Diabetes Insipidus.
  • High levels of Aldosterone, a hormone that causes retention of salts and its excess, may lead to hypernatremia. This condition is called hyperaldosteronism
  • Cushing syndrome in which the adrenal gland produces an excess amount of cortisol that also causes sodium retention.
  • Certain medicines also build up sodium levels in the body, including birth control pills, corticosteroids, lithium, non-steroidal anti-inflammatory drugs (NSAIDs), and laxatives.


Inadequate sodium content in your blood below 135mEq/L may shift the water content from the blood into cells causing the cells to swell up and impair their functioning. This could produce dangerous effects on your brain cells and may generate many other symptoms, including;

  • Nausea and vomiting
  • Dizziness and Headache
  • Exhaustion
  • Loss of appetite
  • Agitation and Hallucination
  • Confusion and disorientation
  • Loss of consciousness
  • Coma

Hyponatremia usually occurs in older patients. Causes of hyponatremia include:

  • Drinking too much water which dilutes blood sodium concentration.
  • Use of medications that decreases blood sodium content, including diuretics, certain painkillers, antidepressants.
  • Kidney disorders which excrete more sodium through urine and certain liver disorders.
  • Heart failure produces sodium excreting hormones.
  • High levels of ADH or Vasopressin causes accumulation of excess water in the body and dilutes the sodium content. The condition is called syndrome of inappropriate ADH secretion (SIADH).
  • Addison's disease in which lack of cortisol leads to excretion of salts.
  • Hypothyroidism
  • High levels of ketones in the blood

Why And When Do You Need To Get Tested?

Your healthcare provider may order this test as a part of your routine assessment; however, you may need this test if:

  • You are suffering from any signs and symptoms of increased and decrease sodium levels.
  • You have a problem with blood pressure.
  • You are taking medicines that alter sodium levels.
  • You are seriously ill or bedridden.
  • You have recent surgery.
  • You are on intravenous fluids.
  • You have kidney, liver, heart, and endocrine disorders.

Your healthcare provider correlates the test report with your physical condition to determine the cause of this imbalance or may run some other tests to reach the diagnosis.

What Type Of Sample Is Required?

A blood sample is drawn from the vein of your arm or hand by using a small needle by a health worker and collected in the test tube or vial.

Do You Need To Prepare For This Test?

You don't need any preparation for this test. However, your healthcare provider may stop certain medications before running this test or may check your glucose levels prior to testing, as elevated glucose levels may affect the results. Be sure that you have informed your healthcare provider about all your medicines.

Is There Any Risk To This Test?

You may feel mild to moderate pain and stinging at the site of the prick, which will alleviate within a few hours, or may experience mild discomfort or bruising, and very rarely, you may encounter infection. If you undergo excessive bleeding from the site of the prick, immediately inform your healthcare provider. 

What Does The Result Mean?

The results may be obtained between 12-48 hours and are usually termed as normal and abnormal.

  • Normal sodium level means your blood has sodium concentration within the normal range of 135-145mEq/L.
  • Abnormally elevated levels of sodium above 145mEq/L and abnormally low levels of sodium below 135mEq/L suggest that you have some underlying cause for this imbalance, which requires further assessment and evaluation. Your healthcare provider may retest you or run some new test for more specific information.

If you have any queries regarding the test results, you should consult your healthcare provider. 

Related Tests:

  • Serum potassium levels
  • Blood urea nitrogen (BUN)
  • Arterial blood gases (ABGs)
  • Electrolyte penal
  • Basic metabolic p
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