Sodium (Na): Electrolyte Balance

What is sodium (Na)

Sodium is the primary extracellular electrolyte, regulating fluid balance, nerve impulse transmission, and muscle contractions. The body does not produce sodium on its own — we get it from food, mainly from table salt (NaCl). The kidneys constantly regulate sodium levels, excreting excess or retaining it when supplies are low.

In blood tests, sodium is marked as Na or Na⁺. It is one of the most commonly tested electrolytes, often included in a metabolic panel or electrolyte panel.

Reference ranges

The standard sodium reference range in blood is 135–145 mmol/L. This range applies to adults of both sexes. Your laboratory may indicate slightly different limits — always follow the ranges specified by your own laboratory.

Sodium levels are quite tightly regulated. Even small deviations from the norm may indicate significant changes in the body, so this marker is evaluated carefully.

Why sodium may be elevated

Hypernatremia (Na > 145 mmol/L) most commonly indicates that the body lacks water. Possible causes:

• Insufficient fluid intake, especially on hot days or during illness.
• Heavy sweating, diarrhea, or vomiting without adequate fluid replacement.
• Uncontrolled diabetes mellitus can increase water loss through the kidneys.
• Certain medications — diuretics, lithium preparations — can affect sodium levels.
• Rarer causes: adrenal disorders (e.g., aldosterone excess), pituitary problems.

Why sodium may be decreased

Hyponatremia (Na < 135 mmol/L) is one of the most common electrolyte disturbances. Possible causes:

• Excessive water intake (polydipsia) — sodium concentration becomes “diluted.”
• Kidney diseases that disrupt sodium retention.
• Heart failure or liver cirrhosis causing fluid accumulation.
• Medications: thiazide diuretics, some antidepressants (SSRIs), anti-inflammatory drugs.
• Hypothyroidism (underactive thyroid).
• Adrenal insufficiency (Addison’s disease) — aldosterone deficiency.
• Intense exercise with large amounts of water but without electrolyte replacement.

What to do next

If sodium levels deviate from the norm, the doctor usually evaluates them together with other markers — potassium, chloride, kidney function tests (creatinine, eGFR), and urine osmolality. A sodium deviation is rarely assessed in isolation — context matters.

If the deviation is slight (131–134 or 146–150 mmol/L), adjusting fluid intake may be sufficient. More significant deviations require thorough investigation to identify the cause.

How to track changes over time

Sodium levels can vary depending on hydration status, medications, and diet. By repeating the test regularly, you can monitor trends. It is especially important to track sodium changes if you take diuretics, are being treated for heart or kidney disease, or have noticed symptoms such as dizziness, nausea, or confusion.

On the QbiLabs platform, you can see your sodium values on a timeline and monitor whether levels are stabilizing or changing.

Questions for your doctor

1. Does my sodium level indicate dehydration, or could there be another cause? 2. Could my current medications have affected my sodium level? 3. Are additional tests needed — urine sodium, osmolality? 4. How should I adjust my fluid and salt intake? 5. Should I repeat the test and after how long?

*This is not medical advice. Consult your doctor for health-related decisions.*