What are sodium disorders?

Sodium is the most abundant electrolyte in the fluid surrounding cells. It controls how water moves between compartments in the body and is essential for maintaining blood pressure, nerve signalling, and cellular hydration. Normal serum sodium ranges from 135 to 145 mmol/L. Deviations outside this range, even modest ones, can significantly affect brain and neurological function.

There are two distinct sodium disorders:

Hyponatraemia is a serum sodium below 135 mmol/L. It is the most common electrolyte disorder encountered in clinical practice. It reflects an excess of water relative to sodium in the body rather than necessarily a sodium deficiency. Mild hyponatraemia is frequently asymptomatic. Severe hyponatraemia below 125 mmol/L causes serious neurological complications and is a medical emergency.

Hypernatraemia is a serum sodium above 145 mmol/L. It almost always reflects a water deficit rather than excess sodium. It is less common than hyponatraemia but carries significant neurological risk when severe. Levels above 160 mmol/L require immediate medical attention.

Sodium disorders affect the brain and nervous system most prominently. Symptoms vary significantly by severity and how quickly the abnormality develops.

Hyponatraemia symptoms:

• Headache, nausea, and fatigue in mild cases

• Confusion, disorientation, and difficulty concentrating

• Muscle weakness, cramps, or twitching

• Irritability and mood changes

• In severe cases: seizures, loss of consciousness, and cerebral oedema requiring emergency treatment

Hypernatraemia symptoms:

• Intense thirst and reduced urine output

• Fatigue, weakness, and restlessness

• Confusion and agitation

• Muscle twitching or rigidity

• In severe cases: seizures, intracranial bleeding, and coma

Both disorders can be entirely asymptomatic in mild forms, making routine blood testing the only reliable detection method.

The causes of hyponatraemia and hypernatraemia are distinct and reflect opposite disturbances in the water and sodium balance.

Hyponatraemia causes:

• Syndrome of inappropriate antidiuretic hormone (SIADH) is the most common cause in hospitalised patients. Excess ADH causes the kidneys to retain water, diluting sodium. It is triggered by lung conditions, brain injury, certain medications, and malignancy.

• Heart failure, liver cirrhosis, and kidney disease cause sodium retention alongside greater water retention, diluting serum sodium.

• Hypothyroidism and adrenal insufficiency impair the body's ability to excrete free water, causing dilutional hyponatraemia.

• Diuretic medications particularly thiazides cause renal sodium loss.

• Excessive fluid intake including overhydration from water alone during endurance exercise can dilute sodium rapidly.

• Vomiting and diarrhoea cause combined sodium and fluid loss with replacement of fluid without sodium.

Hypernatraemia causes:

• Inadequate fluid intake is the most common cause, particularly in older adults, infants, and those with impaired thirst sensation or access to water.

• Diabetes insipidus causes the kidneys to produce abnormally large volumes of dilute urine through ADH deficiency or resistance, rapidly depleting body water.

• Excessive sweating, fever, or diarrhoea cause water loss in excess of sodium loss.

• Hyperglycaemia in uncontrolled diabetes causes osmotic water loss through the kidneys.

• Excessive sodium intake from intravenous saline or sodium-containing medications in a clinical setting.

Sodium disorders are detected directly through blood testing, with supporting markers identifying the underlying cause and assessing systemic impact.

Blood tests Elfcare's panel includes sodium alongside key related markers:

• Serum sodium: the main measurement used to identify if levels are too high or too low.

• Potassium: helps identify causes like diuretic use or adrenal issues when sodium is low.

• Creatinine and eGFR: checks kidney health, as the kidneys are the primary regulators of sodium and water.

• Glucose and HbA1c: high blood sugar can pull water into the blood, making sodium levels appear lower than they actually are.

• Thyroid profile (TSH and T4): screens for an underactive thyroid, which can prevent the body from clearing excess water.

• Cortisol: checks for adrenal gland issues that cause the body to lose salt.

• Albumin and liver markers: identifies if liver disease or poor nutrition is driving sodium imbalances.

• CRP: a marker of inflammation that can trigger a hormonal response (SIADH) that lowers sodium.

• Uric acid: low levels can provide a helpful clue that your body is retaining too much water.

Why early detection matters

Mild sodium disorders are often entirely symptom-free yet place the brain in a state of physiological stress that, if left unaddressed, can progress to serious neurological consequences. Chronic mild hyponatraemia, even when asymptomatic, is independently associated with increased fall risk, cognitive impairment, and bone fractures in older adults. Identifying a sodium disorder early allows for investigation of the underlying cause, whether thyroid disease, adrenal insufficiency, heart failure, or kidney disease, and for treatment that prevents the neurological and systemic consequences of untreated electrolyte imbalance.

How Elfcare can help

Elfcare's blood panel measures serum sodium as standard alongside potassium, creatinine, eGFR, glucose, HbA1c, TSH, albumin, and CRP. This provides both the direct sodium measurement and the metabolic, renal, thyroid, and inflammatory context needed to identify the most likely underlying cause.

The combination of hyponatraemia with abnormal thyroid or cortisol markers, or with kidney or liver disease, provides a clinically important pattern that our comprehensive panel is well positioned to identify.

If our blood tests identify a sodium disorder or related electrolyte imbalance, we take care of further diagnostics or refer you to the appropriate specialist.