Urine Specific Gravity
- Sample Type
- Urine
- Fasting
- No
- Unit
- Ratio
Function
Urine Specific Gravity (USG) measures the concentration of particles in the urine compared to distilled water. It provides a quick assessment of the kidneys' ability to concentrate or dilute urine, which is a direct reflection of a person's hydration status and renal tubular function.
Why it is Ordered
USG is a core component of a routine urinalysis and is ordered to:
- Evaluate hydration status in patients with vomiting, diarrhea, or excessive sweating.
- Monitor patients with suspected Diabetes Insipidus.
- Screen for kidney dysfunction or acute kidney injury.
- Detect the presence of excess substances like glucose or protein in the urine.
Associated Conditions
- Dehydration: Leads to high specific gravity as the kidneys conserve water.
- Diabetes Insipidus: Characterized by very low specific gravity because the kidneys cannot concentrate urine.
- Kidney Failure: Often results in 'isosthenuria,' where the specific gravity is fixed at 1.010, matching the plasma.
- SIADH (Syndrome of Inappropriate Antidiuretic Hormone): Results in excessively concentrated urine despite normal fluid intake.
- Heart Failure: May cause increased USG due to decreased renal blood flow.
Why Context Matters
Urine Specific Gravity is highly sensitive to external factors. A second opinion or re-test is recommended if the patient recently received intravenous (IV) contrast dye for imaging, as this can artificially inflate the specific gravity to very high levels (>1.035). Cold temperatures, high protein intake, or the presence of glucose (glucosuria) in diabetic patients can also skew results. Hydration levels can change rapidly; a result from a morning 'first void' will be significantly different from a post-exercise or post-hydration sample.
Lab ranges are statistical averages, not biological laws. "Normal" for a 20-year-old male isn't normal for a 60-year-old female.
Clinical References
Source-of-truth databases and clinical guidelines for Urine Specific Gravity:
Official Sources
Research & Guidelines
- PubMed: Urine Specific Gravity Clinical GuidelinesNCBI / PubMed
Related Indicators
Medically Reviewed by Dr. Binoy Babu, MBBS
Board Certified Doctor • 10+ Years Clinical Experience
Dr. Babu is a practicing physician dedicated to empowering patients with clear, actionable medical information. He founded 2opi to bridge the gap between complex lab reports and patient understanding, ensuring everyone has access to a reliable second opinion.
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