WHAT IS OSMOLALITY TEST?
Osmolality is a measure of the concentration of particles in the serum per kilogram of water. Osmolarity is nearly the same as osmolality but measures the concentration per litre of water. Used to assess the fluid state of the client and determine the cause of fluid and electrolyte imbalances, particularly in endocrine disorders. The normally functioning osmoregulation system maintains the serum osmolality (the concentration of the blood) within a tight normal range. Receptors in the hypothalamus adjust the level of antidiuretic hormone from the posterior pituitary, which affects the free water excreted from the kidney. Disorders of the hypothalamus, the posterior area of the pituitary, or the kidney may alter serum osmolality. Dehydration from any cause increases osmolality. Overhydration decreases serum osmolality. Either is dangerous to the client. Urine osmolarity is usually obtained with serum osmolality because the comparison gives the true picture of the fluid-balance state. The set of serum electrolytes (especially sodium and glucose) will also be assessed.