Sodium Blood Test: Normal Ranges, Causes & What Your Results Mean

What Is Sodium?

Sodium is the most abundant positively charged ion (cation) in the extracellular fluid and plays a fundamental role in maintaining fluid balance, blood pressure, nerve conduction, and muscle contraction. The body tightly regulates sodium concentration within a narrow range through the coordinated action of the kidneys, antidiuretic hormone (ADH), and the renin-angiotensin-aldosterone system (RAAS).

Serum sodium reflects the balance between water and sodium in the body - it is as much a measure of hydration status as it is of sodium intake. This is why both dehydration and overhydration can cause abnormal sodium levels.

Why Is Sodium Tested?

• Routine electrolyte panel - sodium is part of every U&E (urea and electrolytes) test
• Fluid balance assessment - dehydration, fluid overload, and intravenous fluid therapy
• Medication monitoring - diuretics, ACE inhibitors, and SSRIs can affect sodium
• Confusion or altered consciousness - both hypo- and hypernatraemia cause neurological symptoms
• Heart failure and liver cirrhosis - these conditions commonly cause hyponatraemia
• Post-operative monitoring - sodium shifts are common after surgery

Normal Ranges

What Do High Sodium Levels Mean? (Hypernatraemia)

• Dehydration - the most common cause; insufficient water intake or excessive water loss (diarrhoea, sweating, burns)
• Diabetes insipidus - the kidneys excrete dilute urine due to inadequate ADH (central) or ADH resistance (nephrogenic)
• Excess sodium intake - IV saline administration, excessive salt consumption
• Cushing's syndrome - cortisol excess promotes sodium retention
• Primary hyperaldosteronism (Conn's syndrome) - excess aldosterone causes sodium retention and potassium loss

What Do Low Sodium Levels Mean? (Hyponatraemia)

• SIADH - syndrome of inappropriate ADH secretion, the most common cause in hospitalised patients
• Diuretics - thiazides are the most common drug cause of hyponatraemia
• Heart failure - dilutional hyponatraemia from water retention
• Liver cirrhosis, similar dilutional mechanism
• Excessive water intake, psychogenic polydipsia or overhydration during endurance exercise (exercise-associated hyponatraemia)
• Hypothyroidism - severe hypothyroidism can impair free water excretion
• Adrenal insufficiency - cortisol deficiency impairs renal water excretion
• SSRIs - selective serotonin reuptake inhibitors can cause SIADH, particularly in elderly patients

How to Maintain Healthy Sodium Levels

• Stay appropriately hydrated - drink to thirst; avoid excessive water intake, especially during exercise
• Moderate salt intake - the NHS recommends no more than 6g salt (2.4g sodium) per day
• Monitor medications - if you take diuretics or SSRIs, your GP should check sodium periodically
• Seek urgent care — severe hyponatraemia (Na <125) or hypernatraemia (Na >155) is a medical emergency
• Sports hydration — for exercise lasting over 1 hour, use electrolyte drinks rather than plain water

When Should You Get Tested?

• As part of a routine blood test (U&E panel)
• You are taking diuretics, ACE inhibitors, or SSRIs
• Symptoms of confusion, nausea, headache, or muscle weakness
• After prolonged vomiting, diarrhoea, or heavy sweating
• You have heart failure, liver disease, or kidney disease

Which Lola Health Tests Include Sodium?

Sodium is included in Core Health, Vital Check, and Peak Insights panels as part of the electrolyte profile. Available as an add-on with any Lola Health blood test.