Normal serum osmolality ranges from 280 to 295 mOsm/kg, while normal urine osmolality can vary widely, from 50 to 1200 mOsm/kg, depending on hydration status. 

Here’s a more detailed explanation:

Serum Osmolality:

• Normal Range: 280 to 295 mOsm/kg.Â
• What it measures: Serum osmolality reflects the concentration of dissolved particles (solutes) in the serum, primarily sodium, glucose, and urea.Â
• Importance: It helps assess fluid balance and kidney function.Â

Urine Osmolality:

• Normal Range:50 to 1200 mOsm/kg.
• What it measures:Urine osmolality reflects the kidneys’ ability to concentrate or dilute urine, depending on the body’s hydration status.
• Importance:It helps assess kidney function and fluid balance, and can be used to differentiate between various conditions, such as diabetes insipidus and SIADH.
• Factors affecting urine osmolality:
  • Fluid intake: A higher fluid intake leads to lower urine osmolality (more dilute urine), while lower fluid intake leads to higher urine osmolality (more concentrated urine).
  • Antidiuretic hormone (ADH): ADH, also known as vasopressin, regulates water reabsorption in the kidneys. Higher levels of ADH lead to higher urine osmolality (more concentrated urine), and lower levels of ADH lead to lower urine osmolality (more dilute urine).
  • Kidney function: Kidney disease can impair the ability to concentrate or dilute urine, leading to abnormal urine osmolality.Â