Kidney functionSodium



June 25, 2020

Kidney function

What is Sodium?

Sodium (Na +) is an electrolyte and a mineral that has a fundamental role in maintaining the body's water balance and the regulation of blood pressure. It is also important for our nerves and muscles.

The main source of sodium is table salt, but sodium is found naturally in most of the food we eat. Processed food can sometimes have a very high sodium content without necessarily tasting very salty.

Sodium level in the blood is tightly regulated by our endocrine system via a number of hormones. Most of us eat much more sodium than our bodies actually need. Excess sodium is primarily removed from our bodies by our kidneys, but our bodies can also lose sodium via sweat and stool.

Why is this analysis important?

A sodium test is often ordered by doctors to assess the body’s salt and water balance. Sudden changes in the sodium level in the blood usually causes obvious symptoms that make people seek medical care. However, when the sodium level in the blood gradually changes over an extended period of time, our body will slowly adapt and we may only experience vague symptoms such as fatigue, weakness, swollenness and frequent headaches. It is therefore common to include a blood sodium test in a general health check.

Sodium levels in the blood can also be determined to help evaluate the function of our kidneys and endocrine system. Since our kidneys and endocrine system are crucial for the regulation of sodium levels in our body, problems with these organs can cause the sodium level to become abnormal.

In short, it is useful to analyse sodium levels in the blood to:

  • Assess the body's salt and water balance

  • Assess kidney function

  • Investigate certain diseases of the endocrine system


The reference range for sodium levels in the blood can be different depending on the laboratory and technique used. Doctors usually also take into account a number of factors when evaluating sodium values.

High sodium levels in the blood may be associated with:

  • Dehydration, caused by:

  • - Low water intake

  • - Excessive loss of water from vomiting or diarrhea

  • - Poorly controlled diabetes

  • - Kidney disease

  • - Overuse of certain medications such as diuretics

  • - Excessive urine production (Diabetes insipidus)

  • High salt diet

  • High levels of the hormone aldosterone (Hyperaldosteronism)

Low sodium levels in the blood may be associated with:

  • Loss of sodium, caused by:

  • - Excessive sweating

  • - Excessive loss of salt through diarrhea

  • - Severe burns affecting a large skin area

  • - Abnormally high sodium level in the sweat (Cystic fibrosis)

  • - Overuse of certain medications such as diuretics

  • Dilution of sodium due to increased amount of fluid, as in:

  • - Heart failure

  • - Chronic liver failure (Cirrhosis)

  • - Inappropriate antidiuretic hormone secretion (SIADH)

  • - Excessive water consumption (Polydipsia)

  • Low levels of the hormone aldosterone (Hypoaldosteronism)

  • Underactive thyroid (Hypothyroidism)

Other Considerations

Our bodies strive to maintain a relatively constant level of sodium in the blood. If we get too much sodium from food, our kidneys will have to work very hard to remove the extra sodium in order to keep the level of sodium in the blood stable. Therefore a blood sodium value within the normal range does not necessarily mean that we are eating an optimal amount of sodium.

Very high levels of fat, sugar and protein in the blood can lead to inaccurate readings when measuring sodium levels.

  • A wide range of common drugs can affect sodium levels in the blood, such as certain oral contraceptives, antidepressants, antibiotics, diuretics, antihypertensives and painkillers.

Tests that include this marker


General principles of disorders of water balance (hyponatremia and hypernatremia) and sodium balance (hypovolemia and edema). Richard H Sterns, MD. UpToDate Sep 27, 2018

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