Osmometery in Medicine

Osmolality measurements are used to assess fluid and electrolyte imbalances, diagnose conditions like diabetes insipidus, and monitor patients undergoing dialysis or receiving intravenous fluids. This measurement provides also valuable insights into fluid and electrolyte balance for the kidney function.

Osmolality testing can help identify the presence of toxins like antifreeze or rubbing alcohol in the body, as these substances can significantly alter the osmolality of body fluids. A high plasma osmolality can rarely be due to large amounts of alcohol in the blood. The difference between the osmolality measured in the laboratory and the value calculated from the sodium, potassium, glucose and urea (above) can give an indication of the amount of alcohol present.

Osmolality measurements are used to track the effectiveness of treatments that affect fluid and electrolyte balance, such as diuretic therapy or the administration of osmotically active medications.

The calculated and measured osmolality can be compared to determine if there are other particles present (in addition to sodium, potassium, glucose and urea) that contribute to the measured serum osmolality. The difference between measured and calculated (estimated) osmolality is called the “osmotic gap” or “osmolal gap”. An increase in the osmotic gap (greater than 10) indicates the presence of other substances such as toxic alcohols, aspirin, or mannitol.