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🧪 What is Urine Osmolality?

Urine Osmolality measures the concentration of dissolved particles (solutes) in urine, reflecting the kidney’s ability to concentrate or dilute urine. It is expressed in milliosmoles per kilogram (mOsm/kg) of water.

❓ Why is the Test Done?

To:

Assess renal concentrating ability
Evaluate causes of polyuria and polydipsia
Diagnose and differentiate types of renal tubular disorders
Investigate electrolyte and fluid balance disorders such as diabetes insipidus and syndrome of inappropriate antidiuretic hormone secretion (SIADH)
Monitor hydration status

📊 Normal Range

Urine Osmolality	Reference Range
Typical adult values	300 – 900 mOsm/kg (varies by hydration status)
Maximum concentrating ability	Up to ~1200 mOsm/kg

📈 Interpretation of Results

Result	Clinical Significance
Low urine osmolality	Impaired concentrating ability; diabetes insipidus, renal failure, excessive fluid intake
High urine osmolality	Dehydration, SIADH, prerenal azotemia
Variable values	Depends on hydration, fluid intake, and antidiuretic hormone levels

🧠 Associated Conditions

Condition	Details
Diabetes insipidus	Low urine osmolality despite dehydration
SIADH	Inappropriately concentrated urine (high osmolality)
Acute kidney injury	Impaired urine concentration
Dehydration	Concentrated urine

🔄 Related / Follow-Up Tests

Serum osmolality
Urine sodium
Electrolytes (Na, K)
Water deprivation test (for diabetes insipidus)
ADH levels

✅ Fasting Required?

Test	Fasting Required
Urine Osmolality	❌ No

📝 Summary Table

Parameter	Details
What	Measures concentration of solutes in urine
Why	Assess kidney concentrating function and hydration status
Normal Range	300–900 mOsm/kg (varies)
Low Values	Diabetes insipidus, renal failure
High Values	Dehydration, SIADH
Associated Conditions	Diabetes insipidus, SIADH, acute kidney injury
Follow-up Tests	Serum osmolality, urine sodium, electrolytes
Fasting Required	❌ No

Urine Osmolality

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