Osmolality (Serum)

Osmolality (Serum)

Serum osmolality is increased in hypernatremia, hyperglycemia, uremia, ethanol, methanol, or ethylene glycol overdoses, and in diabetes insipidus.

This test helps check your body's water balance. Your doctor may order this test if you have signs of any of the following:

-Low sodium (hyponatremia) or water loss

-Poisoning from harmful substances such as ethanol, methanol, or ethylene glycol

-Problems producing urine

In healthy people, when osmolality in the blood becomes high, the body releases antidiuretic hormone (ADH).

This hormone causes the kidneys to reabsorb water. This results in more concentrated urine. The reabsorbed water dilutes the blood. This allows blood osmolality to fall back to normal.

Low blood osmolality suppresses ADH. This reduces how much water the kidneys reabsorb. Dilute urine is passed to get rid of the excess water, which increases blood osmolality back toward normal.

Osmolality (Serum)


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  • WHAT IT TESTS: Measures how well various electrolytes dissolve in blood serum.
  • WHY TAKE IT: Determine how well kidneys function.