Urine Specific Gravity
Urine specific gravity (relative density) is a measure reflecting the kidneys’ ability to concentrate or dilute urine, thus maintaining the body’s water-salt balance.
Normal specific gravity values in adults range from 1.005 to 1.025, while in children the norms depend on age and may vary from 1.002 to 1.030.
Urine specific gravity depends on the amount of dissolved substances such as urea, uric acid, creatinine, salts, and other metabolites, as well as on the volume of excreted fluid and time of day.
Factors affecting urine specific gravity include:
- Fluid intake — increased drinking lowers specific gravity, dehydration raises it.
- Kidney function — impaired concentrating ability reduces specific gravity.
- Presence of glucose and protein in urine — increase specific gravity.
- Time of day — specific gravity is usually higher at night than during the day.
Deviations from normal specific gravity may indicate various conditions:
- Increased specific gravity is observed in dehydration, diabetes mellitus, nephrotic syndrome, heart failure, and preeclampsia in pregnancy.
- Decreased specific gravity is characteristic of renal failure, diabetes insipidus, chronic nephritis, polyuria, as well as excessive fluid intake and fasting.
Measurement of urine specific gravity is an important diagnostic test that helps assess kidney function, detect water-salt balance disorders, and monitor the course of various diseases.