• Abnormally low level of sodium in the blood.
  NICHD Pediatric Terminology
  U.S. National Cancer Institute, 2021
• Abnormally low sodium levels in the blood; salt depletion.
  CRISP Thesaurus
  National Institutes of Health, 2006
• An abnormally decreased sodium concentration in the blood.
  Human Phenotype Ontology (HPO)
  The Human Phenotype Ontology Project, 2025
• Deficiency of sodium in the blood; salt depletion. (Dorland, 27th ed)
  NLM Medical Subject Headings
  U.S. National Library of Medicine, 2025
• Lower than normal levels of sodium in the circulating blood.
  NCI
  U.S. National Cancer Institute, 2021
• A disorder characterized by laboratory test results that indicate a low concentration of sodium in the blood.
  Common Terminology Criteria for Adverse Events
  U.S. National Institutes of Health, 2021
• Hyponatremia is decrease in serum sodium concentration < 136 mEq/L (< 136 mmol/L) caused by an excess of water relative to solute. Common causes include diuretic use, diarrhea, heart failure, liver disease, renal disease, and the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Clinical manifestations are primarily...
  Merck Manuals
  Merck & Co., Inc., 2025
• Hyponatremia is defined as a serum sodium level of less than 135 mEq/L and is considered severe when the serum level is below 125 mEq/L. Many medical illnesses, such as congestive heart failure, liver failure, renal failure, or pneumonia, may be associated with hyponatremia.
  Medscape
  WebMD, 2025
• Hyponatremia occurs when the concentration of sodium in your blood is abnormally low. Sodium is an electrolyte, and it helps regulate the amount of water that's in and around your cells.
  Mayo Clinic
  Mayo Foundation for Medical Education and Research, 2025
• Hyponatremia is defined as a serum sodium concentration of <135 mEq/L (normal serum sodium concentration is in the range of 135-145 mEq/L). It is a disorder of water balance reflected by an excess of total body water relative to electrolytes (total body sodium and potassium) leading to low plasma osmolality (i.e., <275 mOsm/kg)....
  Epocrates
  Athenahealth, Inc., 2019
• Sodium deficiency, condition in which sodium is insufficient or is not utilized properly. Sodium is an element that functions with chlorine and bicarbonate to maintain a balance of positive and negative ions (electrically charged particles) in body fluids and tissues. The body receives sodium...
  Encyclopedia Britannica
  Encyclopedia Britannica, Inc., 2025