Le sodium (as Na + ion) is essential in maintaining thewater balance of the body.

It plays a crucial role in regulating the movement of water between the interior and exterior of the cell, and therefore in maintaining the arterial pressure and hydration.

It’s’ion most important of the extracellular medium (liquid outside the cells). In the plasma, it represents 90% of the cations (positive ions) present.

La sodium, that is to say the sodium concentration in the plasma, is therefore finely regulated: sodium intake is mainly through food, and excretion is through the kidneys (and in small amounts through perspiration and faeces).

Testing for serum sodium is usually part of the ionic balance ou electrolyte balance, or blood ionogram, which measures the concentrations of different ions (sodium, potassium, bicarbonates, etc.).

It can be done as part of a check-up (especially in the hospital) or because of certain symptoms that worry the doctor, to look for a hydration disorder or an acid-base imbalance.

It is also useful for the evaluation of diseases of the kidney, digestive tract, endocrine glands and the monitoring of treatment with long-lasting diuretic or anti-inflammatory drugs.

The measurement of natremia is done on a simple blood sample.

It is not performed alone: ​​it is part of the blood ionogram, and other analyzes can be performed at the same time, depending on the case. For example, plasma osmolarity, urinary sodium analysis, measurement of blood sugar, or plasma creatinine which, together with urinary serum content, sodium and creatinine, make it possible to calculate the rate of excretion of sodium.

As a guide, normal blood serum values ​​are between 133 and 143 mmol / L (millimoles per liter). They may vary slightly depending on the source (between 135 and 150 mmol / L approximately).

If the blood serum is too low (<135 mmol / L), we speak ofhyponatremia ; if it is too high (greater than 145 or 150 mmol / L), we speak ofhypernatremia.

Hyponatremia is very common in hospitalized people, especially the elderly or in intensive care. This often goes unnoticed, unless it is brutal and very severe, in which case it can cause digestive signs (disgust with water, vomiting, etc.), muscular disorders (fatigue, cramps) and neurological disorders (disorders of consciousness, convulsions).

The causes are many, but are often related to water retention due to a kidney problem (inability of the kidney to excrete water).

The causes of chronic hyponatremia are, among others:

• Renal causes (advanced chronic renal failure, nephropathy with loss of salt, etc.)
• Adrenal insufficiency
• Taking certain diuretics (thiazides)
• Complication of diabetes (hyponatremia associated with hyperglycemia)
• Nephrotic syndrome, cholestatic jaundice, etc.
• Heart failure
• Cirrhosis
• Hypothyroidism
• Ingestion d’eau excessive (potomanie)

The causes of hypernatremia are also multiple, most often denoting dehydration:

• water loss (diabetes, etc.)
• kidney loss (taking diuretics)
• digestive losses (vomiting, diarrhea, etc.)
• skin losses (burns, excessive sweating, etc.)
• excessive sodium intake (NaCl infusion, seawater ingestion, hypertonic dialysis, Cushing’s syndrome, etc.)

Only the doctor can interpret the results and guide the diagnosis.