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Sodium (Na), Serum

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Serum sodium measurement is used to assess acid-base balance, water balance, water poisoning and dehydration.

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Of the electrolytes measured in the blood, Sodium (Na) has the highest concentration. It is the major cation in extracellular fluid. Sodium plays an important role in acid-base balance and neuromuscular function. It maintains an inverse relationship with blood potassium level. Usually, the body uses what is needed from sodium intake in the diet and the excess is excreted in the urine. This balance is regulated by several mechanisms. Any problem with any of the regulatory mechanisms can cause abnormal levels of sodium in the blood. These mechanisms include the production of hormones that increase (natriuretic peptide) or decrease (aldosterone) the elimination of sodium in the urine and the production of antidiuretic hormone (ADH) that prevents water loss. Another mechanism is thirst. When sodium levels rise in the blood, thirst is created, and the resulting intake of water helps to return Sodium to blood levels.

The concentration of sodium in the blood is closely related to the balance of body fluids, and in fact, its concentration stimulates the kidneys to compensate for changes in body fluid balance. For example, as the body's water increases, the sodium concentration decreases. This stimulates the kidneys to compensate through sodium retention and water excretion. This process is accomplished through the action of aldosterone. If the water in the body decreases, the sodium concentration in the blood increases. This activates the secretion of the antidiuretic hormone, resulting in water retention.

Blood sodium is measured when the patient has symptoms of sodium imbalance or disorders associated with abnormal sodium levels. The state of reduced sodium levels in the blood is called hyponatraemia. Signs of this imbalance include lethargy, confusion, abdominal cramps, anxiety, oliguria, rapid and weak pulse, headache, reduced skin tenderness, tremor, convulsions and possibly coma. Hypernatraemia is a condition where blood sodium levels are above normal. Signs of this imbalance include dry mucous membranes, fever, thirst, and anxiety.

Possible Interpretations of Pathological Values
  • Increase (Hypernatraemia): Congestive heart failure, Cushing's disease, dehydration, diabetes mellitus, sweating, diarrhea, hyperaldosteronism, hypertension, hypokalaemia, salicylate toxicity, toxinemia, vomiting-syndrome. Medications: ACTH, androgens, ampicillin, calcium, carbenicillin, carbenoxolone, clonidine, corticosteroids, diazoxide, estrogens, gamma-hydroxybutyrate (GHB), guanethidine, lactulose, mannitol, methoxyflurane, methyldopa, mineralocorticoids, oral contraceptives, oxyphenbutazone, phenylbutazone, alkaloids, reserpine, sodium bicarbonate, tetracycline. Herbal or natural remedies that include licorice.
  • Decrease (Hyponatraemia): Addison's disease, adrenal insufficiency, aminoglycoside toxicity, ascites in heart failure, intestinal obstruction, burns, cerebral palsy, chronic renal failure, liver cirrhosis, plasma hyperosmotility, hyperthermia, hypophosphatemia, hypotension, hypothyroidism, hysterectomy, malabsorption, malnutrition, meningitis, metabolic acidosis, myxoids, nephrotic syndrome, hyperhydration, pain (abdominal pain), puncture, paralytic ileus, psychogenic polydipsia, pyelonephritis (chronic), renal hypertension, sigmoidoscopy, diarrhea, inappropriate antidiuretic hormone secretion syndrome, toxinemia, toxic shock syndrome, vomiting. Medications: aminoglutethimide, ammonium chloride, amphotericin B, carbamazepine, chlorpropamide, cisplatin, chlorpropamide, cyclophosphamide, diuretics (loop: ethacrynic acid and furosemide, osmotic mannitol, thiazide: hydrochlorothiazide), fosinopril, heparin, laxatives, miconazole, NSAIDs (NSAIDs), oxytocin, spironolactone, sulfonylureas, tolbutamide, tricyclic antidepressants, valproic acid, vasopressin, vincristine




Important Note

Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. Correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".

Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.

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