Sodium – role, research, standards. Excess and deficiency of sodium in the blood

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Sodium is an electrolyte and a mineral necessary for the proper functioning of the human body. It helps to maintain water balance (the amount of fluid inside and outside the body’s cells) and electrolyte balance in the body. Sodium plays an important role in maintaining the proper functioning of the muscles and nervous system. What other important role does sodium play in the body? What causes its excess and what causes its deficiency? You will get the answers below.

Sodium – characteristics

Sodium is one of the electrolytes found in body fluids in the form of positive ions (extracellular cations) or negative ions (anions). Sodium is supplied to the body with the diet and eliminated by the kidneys in the urine and to some extent in the faeces and sweat. Sodium excretion is regulated by natriuretic peptides (promoting sodium removal). Conversely, vasopressin and aldosterone both retain sodium in the body.

Excess sodium in the body is perceived as thirst, only drinking a certain amount of fluid causes the blood to dilute and the sodium returns to its normal concentration. Any abnormalities and disturbances in these mechanisms lead to unpleasant symptoms, e.g. edema and dehydration.

Such conditions can contribute to many abnormal conditions. Therefore, the assessment of sodium concentration is one of the most frequently performed laboratory tests. Due to its properties, sodium fulfills many important functions in the human body.

Sodium – functions

The most important functions of sodium are:

1. sodium regulates the amount and distribution of water in the human body,
2. is responsible for maintaining the difference in electric potentials on both sides of the cell membrane (thanks to which it is possible for all elements of the body to function and cooperate),
3. affects the maintenance of the proper pH (acid-base balance).

Sodium – role in the body

The total amount of sodium in your body affects the amount of fluid in your blood (blood volume). The body constantly monitors blood volume and sodium concentration. When any of these become too high, “sensors” in the heart, blood vessels and kidneys detect the growth and stimulate the kidneys to excrete sodium, thus restoring normal blood volume.

When the blood volume or sodium concentration becomes too low, sensors activate mechanisms to increase the blood volume. These mechanisms include:

1. the kidneys stimulate the adrenal glands to secrete the hormone aldosterone. It causes the kidneys to trap sodium and excrete potassium. When sodium is retained, less urine is produced which eventually causes blood volume to increase.
2. The pituitary gland secretes vasopressin (sometimes called an antidiuretic hormone). Vasopressin causes water to be reabsorbed in the renal tubules.

Also read: What are the functions of potassium in the body?

Sodium – Why Is It So Important for Older People?

As we age, the body becomes less able to maintain a water-sodium balance for several key reasons:

1. reduced thirst – older people do not feel much thirst with age, therefore they do not drink a lot of fluids,
2. changes in the kidneys – aging kidneys may be less able to recover water and electrolytes from the urine, as a result of which more water may be excreted in the urine,
3. less fluid in the body – in the elderly, the body contains less fluid. Only 45% of body weight is fluid in older people, compared with 60% in younger people. This change means that the slight loss of fluid and sodium, which may be due to a fever or not getting enough food and drink, could have more serious consequences in older adults.
4. Inability to get water – Some older people have physical problems that prevent them from getting something to drink when they are thirsty. Others may have dementia that may prevent them from realizing that they are thirsty or from expressing it.
5. Medications: Many older people are taking medications for high blood pressure, diabetes, or heart disease that can cause excess fluid to be excreted.

The above conditions can cause fluid loss or insufficient fluid intake, and thus can cause high blood sodium levels and / and dehydration. Since these situations are more common among the elderly, hypernatremia is more common among them.

Hypernatremia is poorly tolerated by the elderly and can lead to confusion, coma and even death in severe cases.

Excess fluid and sodium are more common in older adults because the disorders that usually cause excess fluid – heart failure, liver disorders, and kidney disease – are more common in this age group.

Low blood sodium levels (hyponatraemia) are more common in older people. Hyponatraemia usually occurs when the body retains too much fluid, such as in the case of heart failure or liver disease.

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Hyponatraemia also occurs in older people who take certain types of diuretics (thiazide diuretics such as hydrochlorothiazide), especially if the kidneys are not working properly. Diuretics are sometimes called water pills. Using liquid dietary supplements or ingesting low-sodium intravenous fluids in a hospital can also cause hyponatraemia in seniors.

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When do we do the sodium test?

The most common indications for a sodium (Na) test are listed below:

1. prolonged diarrhea, vomiting,
2. staying in high temperature, feverish states,
3. excessive urination
4. refraining from taking meals and liquids,
5. swelling
6. chronic diseases of the heart, liver, kidneys. In these ailments, disturbances in the concentration of electrolytes, including sodium, are observed,
7. behavioral disorders,
8. suspicion of brain edema,
9. systematic health monitoring. Any deviation in sodium concentration may be a symptom of developing abnormalities. Often, the immediate detection of disorders allows for better treatment results. It is worth mentioning that slow changes in sodium concentration may not produce any symptoms until they are significantly intensified.
10. assessment of pH (acid-base balance of the body),
11. water management assessment. Sodium is involved in maintaining the proper composition of the body’s fluids. Ailments in the form of hyperhydration or dehydration are usually associated with changes in its concentration,
12. monitoring the treatment of patients taking diuretics and treated with intravenous fluids,
13. controlling the condition of patients after serious infections, operations and injuries,
14. hypernatremia (increased sodium concentration) manifested by: vomiting, loss of appetite, high blood pressure, excessive thirst, problems with coordination, muscle tremors, and sometimes even coma,
15. hyponatraemia (low sodium levels) manifested by: nausea, vomiting, low blood pressure, headache, fits, confusion, difficulty concentrating and sometimes coma. 

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Sodium – the course of the study

Preparation for sodium test: on an empty stomach (at least 8 hours). One day before the examination, physical exertion and alcohol consumption should be avoided. The medications you take may also affect the test result, so you need to inform your doctor about all medications you are taking.

The course of the sodium test: one-time blood sampling from a vein in the arm. After removing the needle, it is recommended that you apply pressure to the injection site for several minutes to prevent bleeding. The blood sample taken from the patient is analyzed using a special device.

The waiting time for the sodium test result: 1 Day.

Comments: In addition to true hyponatraemia, pseudohyponatraemia also occurs as a result of increases in serum glucose or lipids. Before performing the test, inform the laboratory staff about the possible carrier of pathogens that are transmitted through the blood, such as HBV, HCV or HIV.

Sodium – standards

The norms of sodium in the blood are 135-145 mmol / l.

Sodium standards may vary depending on the laboratory where the test was performed and the test method. Therefore, together with the test result, a reference range appropriate for a given laboratory should be provided.

Often, when the correct value is exceeded, next to the result, H (High) is given, and in the case of a drop below the L (Low) standard.

Excess sodium in the blood – hypernatremia

Sodium is one of the body’s electrolytes that, when dissolved in body fluids such as blood, carries an electrical charge. In hypernatremia, the body contains too little water in relation to the amount of sodium. Blood sodium levels become abnormally high when the water loss exceeds the sodium loss.

Usually, hypernatremia is the result of dehydration. For example, people can lose body fluids and become dehydrated because of:

1. too little fluid intake,
2. vomiting
3. diarrhea
4. the use of diuretics (drugs that increase urination)
5. excessive sweating.

However, it is inadequate water intake that usually plays a key role.

People with diabetes and high blood sugar may urinate in excessive amounts, causing dehydration. Dehydration can also be caused by kidney problems and diabetes insipidus, which also causes people to pass excessive amounts of urine, albeit without high blood sugar, and is caused by inadequate or ineffective secretion or action of vasopressin. Hypernatremia usually causes thirst.

Rarely, adrenal gland disorders can cause mild hypernatraemia without dehydration. Salt over-administration (usually in hospitalized patients) is another rare cause of hypernatremia. Hypernatremia is most common in the elderly.

The diagnosis of hypernatremia is based on blood tests that indicate high sodium levels.

Doctors may perform further tests to identify the cause of the hypernatraemia, including measurements of urine volume and concentration. A special test called the water deprivation test is useful in identifying some causes, such as diabetes insipidus.

Hypernatremia is treated by replacing the fluids. In all but mild cases, intravenous fluids (containing water and a small amount of sodium in carefully selected concentrations) are administered intravenously. The level of sodium in the blood decreases slowly because lowering too quickly can cause permanent damage to the brain.

See also: Brain damage disrupts sleep

Blood sodium deficiency – hyponatraemia

Hyponatraemia occurs when your body contains too little sodium for the amount of fluid it contains. The body may have too much, too little or the normal amount of fluid. However, in all cases, sodium levels are lowered. For example, people with severe vomiting or diarrhea lose sodium. If they replace fluid losses with water alone, the sodium is diluted.

Disorders such as kidney disease (for example glomerulonephritis) and other disorders such as cirrhosis and heart failure can cause sodium and fluid retention in the body. Often times, the body retains more fluid than sodium, which means the sodium is diluted.

Under certain conditions, people can drink too much water (polydipsia), which can contribute to the development of hyponatraemia. Thiazide diuretics (sometimes called water pills) are a common cause of hyponatraemia. These drugs increase the excretion of sodium, which increases the excretion of water. Thiazide diuretics are usually well tolerated but can cause hyponatraemia in people prone to low sodium levels, especially the elderly.

Vasopressin (also known as anti-diuretic hormone) is a substance produced naturally in the body that helps regulate the amount of water in the body by controlling the amount of water that is excreted by the kidneys. Vasopressin reduces the amount of water produced by the kidneys, which keeps more water in the body and dilutes the sodium.

The pituitary gland produces and releases vasopressin when blood volume (the amount of fluid in blood vessels) or blood pressure drops, or when electrolytes (such as sodium) become too high. Chronic pain, stress, exercise, low blood sugar, and certain diseases of the heart, thyroid, kidney, or adrenal glands can stimulate the release of vasopressin from the pituitary gland.

A common cause of hyponatraemia is syndrome of inappropriate antidiuretic hormone secretion (SIADH), in which vasopressin is inappropriately secreted in conditions such as certain cancers, infections and brain diseases.

Other causes of hyponatremia include:

1. Addison’s disease (adrenal insufficiency),
2. blockage of the small intestine
3. burns, if severe,
4. cirrhosis,
5. consuming too much water, as is the case in some mental disorders
6. diarrhea,
7. drugs such as barbiturates, carbamazepine, chlorpropamide, clofibrate, diuretics (most common), opioids, tolbutamide and vincristine,
8. heart failure
9. Hypothyroidism,
10. kidney disorders,
11. inflammation of the pancreas,
12. peritonitis (inflammation of the abdominal cavity)
13. Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH),
14. vomiting.

Read: Vomiting – what is it caused and how to deal with it?

Hyponatremia – Symptoms and Treatment

The brain is especially sensitive to changes in the level of sodium in the blood. Therefore, symptoms of brain dysfunction, such as slowness (lethargy) and confusion, first appear. If blood sodium levels drop quickly, symptoms tend to develop rapidly and are more severe. Older people are more likely to have severe symptoms.

As the hyponatraemia worsens, muscle tremors and convulsions may occur. People may become unresponsive, only aroused by vigorous stimulation (dementia), and ultimately may not become aroused (coma). In the most serious cases, death may occur.

Hyponatraemia is diagnosed by measuring the level of sodium in the blood. Determining the cause is more complex. Doctors take into account a person’s situation, including other current disorders and medications. Blood and urine tests are performed to assess the amount of fluid in the body, blood levels, and urine content.

Mild hyponatraemia can be treated by restricting fluid intake to less than about 1 liter per day. If the cause is a diuretic or other medication, the dose is reduced or the drug is discontinued. If the cause is a disorder, it should be treated first.

Some people, especially those with syndrome of inappropriate antidiuretic hormone secretion, require long-term treatment for hyponatraemia. Mere fluid intake is often not enough to prevent recurrence of hyponatraemia. Salt tablets can be used in people with mild to moderate chronic hyponatraemia. Depending on the cause of the hyponatraemia and the amount of fluid in the person’s body, several medications are available.

Severe hyponatraemia is a medical emergency. To treat it, doctors slowly increase the sodium level in the blood with intravenous fluids and sometimes with diuretics. Sometimes newer drugs, called vaptans, are needed. Increasing sodium levels too quickly can cause serious and often permanent brain damage.

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