Dr. med. Dirk Manski

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Sodium (Natrium) Serum Blood Test

Sodium is the most important positively charged electrolyte (cation) in the extracellular space. It is involved in volume regulation and numerous physiological processes in the cell and at the cell membrane (membrane potential or transport processes).

Standard value:

135–145 mmol/l

Laboratory test method:

Measurement with ion-selective electrode or flame photometer.


Measurement of sodium in serum is indicated in disorders of fluid, electrolyte and acid-base homeostasis.

Differential Diagnosis of Hyponatriemia:

Hyponatriemia is a low concentration of sodium in the blood, this causes an osmotic shift of water into the cell with swelling. The consequences are nausea, vomiting, confusion, vigilance disorders and coma. Further differentiation depends on volume status (assess vital signs, central venous pressure, skin turgor, mucous membranes, peripheral edema, and blood urea nitrogen and serum osmolality):

Hypervolemic hyponatriemia:

Increased extracellular fluid (ECF) volume leads to a reduced sodium concentration due to dilution: hypothyroidism, inappropriate antidiuretic hormone secretion, paraneoplastic (bronchus, pancreas, Hodgkin's disease), chronic lung disease, trauma, postoperative situations, heart failure, liver cirrhosis, nephrotic syndrome, kidney failure.

Hypovolemic hyponatriemia:

Reduced extracellular fluid volume with an even greater deficit of sodium: diuretic therapy, adrenocortical insufficiency (Addison's disease), salt restriction in chronic kidney disease, chronic diarrhea or vomiting, ileus, burns.

Differential Diagnosis of Hypernatremia:

Hypernatremia is a high concentration of sodium in the blood. This leads to intracellular water loss with cell shrinkage: dry skin and mucous membranes, muscle weakness, spasms, dizziness, tachycardia, vigilance disorders, Coma. The symptoms are aggrevated by hypovolemia.

Hypovolemic hypernatremia:

Inadequate intake of free water associated with total body sodium depletion: e.g. profuse sweating, thirst, diarrhea, burns.

Hypervolemic or euvolemic hypernatremia:

Iatrogen, medication, fever, Cushing syndrome, hyperaldosteronism, diabetes insipidus.

Index: 1–9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


Guder, W. G. & Nolte, J.
Das Laborbuch für Klinik und Praxis
Urban + Fischer, 2009

Siegenthaler 1988 SIEGENTHALER, W. ; SIEGENTHALER, W. (Hrsg.):
Differentialdiagnose innerer Krankheiten.
Georg Thieme Verlag, Stuttgart, New York., 1988

  Deutsche Version: Elektrolyte im Serum: Natrium