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Sodium plays many important roles in the body. It maintains fluid balance and is a main nutrient used in nerve impulse transmission and muscle contraction. The normal range for blood sodium is between 135 and 145 mEq/L (3.10 mg/ml to 3.34 mg/ml). Higher levels of sodium are normally associated with hypertension. A sodium level of 150 mEq/L (3.45 mg/ml) or more is known as hypernatremia, a condition that is commonly caused by dehydration or eating too much salt. However it can also be caused by other conditions such as diabetes or hormonal imbalances.
Hyponatremia is an important and common electrolyte abnormality that can be seen in isolation or, as most often is the case, as a complication of other medical illnesses (eg, heart failure, liver failure, renal failure, pneumonia). The normal serum sodium level is 135-145 mEq/L. Hyponatremia is defined as a serum sodium level of less than 135 mEq/L. Joint European guidelines classify hyponatremia in adults according to serum sodium concentration, as follows: Mild: 130-134 mmol/L.