Sodium Test: Purpose, Normal Range and Price

The Sodium test is a blood test that measures the concentration of sodium, the most abundant extracellular cation in the human body and the primary determinant of extracellular fluid osmolality and volume. Sodium governs the distribution of water between intracellular and extracellular compartments through osmotic forces, and its concentration in the blood is maintained within an extraordinarily narrow physiological range through the integrated actions of the hypothalamic thirst mechanism, antidiuretic hormone secretion from the posterior pituitary, and renal tubular sodium reabsorption regulated by the renin-angiotensin-aldosterone system and atrial natriuretic peptide. Sodium is essential for the generation and transmission of electrical impulses in nerve and muscle cells, the regulation of blood pressure and plasma volume, the active transport of glucose and amino acids across cell membranes through sodium-coupled cotransport mechanisms, and the maintenance of normal cellular hydration and function throughout the body. The kidneys are the primary organs responsible for sodium homeostasis, excreting or retaining sodium in precise quantities to maintain plasma osmolality at approximately 280 to 295 milliosmoles per kilogram regardless of wide variation in dietary sodium intake and fluid consumption. Disorders of sodium balance are among the most common electrolyte abnormalities encountered in clinical practice worldwide and in India, where diarrhoeal disease, heat-related illness, chronic kidney disease, cardiac failure, liver cirrhosis, and syndrome of inappropriate antidiuretic hormone secretion collectively account for a substantial proportion of hospitalised patients with electrolyte disturbances. Both hyponatraemia and hypernatraemia carry significant morbidity and mortality when severe, making accurate sodium measurement a critical investigation across virtually every clinical setting. The test is performed on a small blood sample drawn from a vein and completed in under five minutes.

Doctors prescribe a Sodium test in the following situations: Investigating hyponatraemia in patients with nausea, headache, confusion, seizures, and altered consciousness where low serum sodium indicates dilutional or depletional sodium deficit requiring urgent characterisation of the underlying cause to guide appropriate fluid and sodium management and prevent life-threatening cerebral oedema from overly rapid correction. Evaluating dehydration and hypernatraemia in patients with inadequate fluid intake, excessive insensible losses from fever and sweating, osmotic diuresis from uncontrolled diabetes, and central or nephrogenic diabetes insipidus where elevated serum sodium reflects water deficit relative to sodium and guides the rate and composition of fluid replacement therapy. Monitoring patients with heart failure, liver cirrhosis, and nephrotic syndrome where dilutional hyponatraemia from neurohormonal activation and water retention is a common complication, a recognised marker of disease severity, and an independent predictor of adverse clinical outcomes guiding escalation of diuretic therapy and specialist management. Assessing adrenal insufficiency and Addison's disease where hyponatraemia combined with hyperkalaemia is the classical electrolyte pattern reflecting aldosterone deficiency with impaired renal sodium retention and potassium excretion, and where urgent cortisol and ACTH measurement alongside sodium guides emergency hydrocortisone replacement. Evaluating syndrome of inappropriate antidiuretic hormone secretion in patients with hyponatraemia, low plasma osmolality, and inappropriately concentrated urine in the context of central nervous system disease, pulmonary pathology, malignancy, or medication effect where sodium measurement is the cornerstone investigation guiding fluid restriction and specific pharmacological management. Monitoring patients receiving intravenous fluid therapy, total parenteral nutrition, and nasogastric feeding where serial sodium measurements ensure that fluid and electrolyte composition of administered preparations maintains plasma sodium within the safe physiological range throughout the treatment course.

The Sodium test measures the concentration of sodium ions in the blood serum, expressed in milliequivalents per litre (mEq/L) or millimoles per litre (mmol/L). The normal reference range for adults is 136 to 145 mEq/L, with no clinically significant variation by gender and only minor age-related changes in elderly individuals where subtle impairment of renal concentrating and diluting capacity narrows the physiological range. Normal (136 to 145 mEq/L) A result within the normal range indicates that extracellular sodium concentration and osmolality are within the safe physiological range for normal neurological, cardiac, and cellular function. In patients being monitored during fluid therapy or diuretic treatment, a normal sodium confirms that current management is maintaining adequate electrolyte balance without clinically significant deviation in either direction. Low Sodium or Hyponatraemia (Below 136 mEq/L) A serum sodium below 136 mEq/L confirms hyponatraemia, classified as mild at 130 to 135 mEq/L, moderate at 125 to 129 mEq/L, and severe below 125 mEq/L. Mild hyponatraemia may be asymptomatic, while moderate to severe hyponatraemia causes headache, nausea, confusion, seizures, and potentially fatal cerebral oedema requiring prompt but carefully titrated sodium correction to avoid osmotic demyelination syndrome from excessively rapid reversal. Elevated Sodium or Hypernatraemia (Above 145 mEq/L) A serum sodium above 145 mEq/L confirms hypernatraemia, indicating water deficit relative to sodium content most commonly from inadequate fluid intake, excessive water losses, or diabetes insipidus. Hypernatraemia causes cellular dehydration manifesting as intense thirst, lethargy, confusion, and in severe cases cerebral shrinkage with intracranial haemorrhage requiring gradual water replacement at a carefully controlled rate to avoid cerebral oedema from excessively rapid correction.

Fasting for 8 hours before the Sodium test is generally recommended when ordered as part of a comprehensive metabolic or electrolyte panel, ensuring standardised conditions across all co-ordered parameters. Water is permitted during the fasting period, and maintaining adequate hydration before the test is particularly important as dehydration itself can influence sodium levels and introduce a pre-analytical variable that complicates result interpretation. Maintain your normal fluid intake pattern in the hours preceding the test unless your doctor has specifically advised fluid restriction, as both dehydration and excessive water loading in the hours before sampling can transiently shift serum sodium outside the normal range and produce a result that does not accurately reflect your true steady-state sodium status under normal daily conditions. Inform your doctor about all medications currently being taken before the test, particularly diuretics, ACE inhibitors, ARBs, NSAIDs, antidepressants including SSRIs and tricyclics, antiepileptics, antipsychotics, and any intravenous fluids or oral rehydration solutions recently administered, as these significantly influence sodium regulation and renal handling and are essential context for accurate clinical interpretation of your result. If you are undergoing serial sodium monitoring during treatment for hyponatraemia or hypernatraemia, consistent timing and use of the same laboratory platform ensures reliable trend assessment and safe titration of correction therapy. Staying well hydrated before the blood draw facilitates easier venous access and a smooth collection experience.

If you are booking through the SecondMedic platform the Sodium test price starts at approximately Rs. 245. The exact price will be confirmed at the time of booking through SecondMedic. If your doctor has prescribed multiple tests alongside Sodium, SecondMedic health packages include Sodium as part of a broader electrolyte and metabolic panel at a significantly lower combined price.

SecondMedic offers convenient home sample collection for the Sodium test across India, making it easy to get tested without visiting a diagnostic centre. Home collection is available free of charge for orders above Rs. 300. A trained phlebotomist will visit your preferred address between 7 AM and 10 PM, seven days a week, including Sundays and public holidays. Your blood sample is processed at NABL-accredited partner laboratories, and your report is delivered within 24 hours directly to your WhatsApp and email.