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S -Na

S -Na

Sodium is one of the most important salts in the body, and it is present in all bodily fluids. Sodium is involved in nerve function, regulation of water and acid/base balance in the body, and regulation of the concentration of blood (osmolality). The body needs balanced sodium levels to support normal metabolism.

The body maintains balanced blood sodium levels through different means:

  • the body produces hormones that can increase or decrease the excretion of sodium in the urine
  • the body produces a hormone that prevents water from being released from the body
  • the body controls the feeling of thirst. Even a one per cent increase in blood sodium level makes you feel thirsty and gets you to drink, which restores the sodium level towards normal.

The body obtains sodium through food. Common salt is a compound of sodium and chloride. The body regulates the sodium level by regulating its secretion from the kidneys. Hormones like aldosterone (S-Aldo) and cortisol (S-Korsol) are involved in the regulation of sodium levels. When the amount of water in the body is higher than normal, the ratio of sodium to water decreases, meaning that the solution is diluted. Correspondingly, the solution is concentrated when there is too little water in the body. Therefore, in order to correct the sodium balance in the body, we need to regulate hydration.

When should sodium be measured?

Blood sodium level is often measured as part of a routine check-up and when examining various diseases. Most commonly, sodium is tested when examining various heart, vein, and kidney diseases, together with potassium and creatinine.

The sodium examination is used for assessing the fluid and electrolyte balance in the body. The following symptoms can occur when the sodium balance is disturbed:

  • Feeling of thirst
  • Swelling
  • Vomiting
  • Diarrhoea
  • Restlessness
  • Fatigue
  • Arrhythmia
  • Loss of strength
  • Restlessness
  • Dry mucosa (mouth, eyes)
What does a sodium test measure?

The majority of sodium in the body is inside cells, and only a fraction of it is in the bloodstream. The body regulates the level of sodium carefully. The sodium test tells us about the fluid balance of the body. Changes in the concentration reflect the ratio between water and sodium in particular, not sodium deficiency or excess sodium in the body. Additional tests can be done to find out the cause of a high or low level of sodium.

Reference values: 137–145 mmol/l

Children under 17 years old: 30 – 140 mmol

If the blood sodium level decreases below 125 mmol/l, it typically leads to fatigue, loss of strength, headache, nausea, and muscle cramps. When the sodium level decreases even further, nervous symptoms and muscle weakness, convulsions, and disorientation can occur.

Read more about defining reference values.

Please contact your physician or other healthcare professional if you suspect an illness or need help interpreting the results.

Elevated sodium levels (hypernatraemia) are caused by the body not receiving enough water to replace lost water and the body being dehydrated. Not drinking enough is the most common reason for hypernatraemia. Increased water loss as a result of diarrhoea, vomiting, and disorders in the production of fluid balance-regulating hormones can also lead to increased levels of sodium in the blood. Abundant evaporation of water from the skin due to fever or a burn, for example, can increase blood sodium levels.

The most common reason for low sodium (hyponatraemia) is dilution. In this case, water intake exceeds water lost. Low sodium levels are common in people with heart failure. Another significant cause is high loss of sodium due to sweating, for example.

Low sodium levels can be caused by the following factors:

  • Excessive hydration
  • Strong sweating
  • Burns
  • Diarrhoea, vomiting
  • Drinking copious amounts of water
  • Kidney failure
  • Heart failure
  • Liver cirrhosis
  • Addison’s disease, or deficiency of “salt hormone”
  • Use of certain medicinal agents
  • Cortisol balances blood sugar to make sure that the body’s intake is adequate (2129 S-Korsol)
  • Potassium is one of the most important minerals in the blood (2001 S-K)
  • Calcium is critical for all cells of the body (2013 S-Ca, 6032 S-Ca-Albk)


Fasting is not required

This examination does not require fasting