Urine specific gravity

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Urine specific gravity measurement using a refractometer.

Urine specific gravity (USG) is a measure of the concentration of solutes in the urine. It is a valuable diagnostic tool used to assess the kidney's ability to concentrate or dilute urine and is an important parameter in evaluating a patient's hydration status and renal function.

Physiology

The kidneys play a crucial role in maintaining the body's fluid and electrolyte balance. They filter blood, reabsorb essential substances, and excrete waste products in the form of urine. The specific gravity of urine reflects the kidney's ability to concentrate or dilute urine relative to plasma.

Urine specific gravity is influenced by the amount of solutes such as electrolytes, urea, and glucose present in the urine. A higher specific gravity indicates more concentrated urine, while a lower specific gravity suggests more dilute urine.

Measurement

Urine specific gravity can be measured using a refractometer, a urinometer, or reagent strips. The refractometer is a precise instrument that measures the refractive index of urine, which correlates with its specific gravity. Reagent strips provide a quick and convenient method but may be less accurate.

Clinical Significance

Dehydration

In cases of dehydration, the body conserves water, leading to more concentrated urine and a higher specific gravity. Monitoring urine specific gravity can help assess the severity of dehydration and guide rehydration therapy.

Renal Disorders

Urine specific gravity is an important parameter in diagnosing and monitoring renal disorders. In conditions such as chronic kidney disease, the kidneys may lose their ability to concentrate urine, resulting in a fixed low specific gravity.

Diabetes Insipidus

In diabetes insipidus, the kidneys are unable to concentrate urine due to a deficiency of antidiuretic hormone (ADH) or a lack of response to ADH. This results in the production of large volumes of dilute urine with a low specific gravity.

Related Pages

• Kidney function tests
• Urinalysis
• Dehydration
• Chronic kidney disease
• Diabetes insipidus