American Board of Internal Medicine (ABIM) Certification Practice Exam

What urine osmolality value indicates concentrated urine?

1. Above 100 mOsm/kg H2O

2. Below 50 mOsm/kg H2O

3. Exactly 200 mOsm/kg H2O

4. Above 300 mOsm/kg H2O

The correct answer is: Above 300 mOsm/kg H2O

The value that indicates concentrated urine is above 300 mOsm/kg H2O. Normal urine osmolality typically ranges from about 300 to 900 mOsm/kg, depending on the hydration status of the individual and the body's need to concentrate waste products. When urine osmolality exceeds 300 mOsm/kg H2O, it reflects the kidney's ability to concentrate urine effectively, typically as a response to dehydration, high solute intake, or certain hormonal signals, such as antidiuretic hormone (ADH). In contrast, values below 300 mOsm/kg, including those below 100 or 50 mOsm/kg, indicate dilute urine, which suggests an inability to concentrate urine properly due to various conditions such as excessive hydration, kidney disorders, or hormonal imbalances. A specific value of exactly 200 mOsm/kg would also fall into the diluted urine category, further confirming that values above 300 mOsm/kg signify concentrated urine.