Osmolality
Definition This test measures the osmolality (concentration of particles) of serum (the fluid portion of blood, without fibrinogen).
Why is the Test Performed?
Osmolality measures the concentration of particles in solution. Osmolality increases with dehydration and decreases with overhydration. In normal people, increased osmolality in the blood will stimulate secretion of ADH (antidiuretic hormone). This will result in increased water reabsorption, more concentrated urine, and less concentrated plasma. A low serum osmolality will suppress the release of ADH, resulting in decreased water reabsorption and more concentrated plasma.
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