Urine Specific Gravity (SG): What It Means

What is urine specific gravity?

Urine specific gravity (SG) is a measure that reflects urine concentration — specifically, how many dissolved substances are present compared to pure water. The specific gravity of pure water is 1.000. The more substances dissolved in urine, the higher its specific gravity.

This measure helps assess the kidneys' ability to concentrate or dilute urine. The kidneys constantly regulate how much water is retained in the body and how much is excreted with urine — this is one of the key mechanisms for maintaining water and electrolyte balance.

Urine specific gravity is measured as part of a routine urinalysis, most commonly using an automated analyzer or refractometer. It is a non-invasive, simple, and quick test that provides valuable information about hydration status and kidney function.

Normal ranges (reference values)

A normal urine specific gravity ranges from 1.005 to 1.030. This wide range reflects broad physiological variation, as urine concentration changes depending on fluid intake, physical activity, ambient temperature, and other individual factors.

In the morning, after overnight rest, specific gravity is usually higher — the body retained water during sleep. After drinking large amounts of fluids, specific gravity decreases as the kidneys actively excrete excess fluid. Both situations are normal physiological adaptations.

Values below 1.005 may indicate very dilute urine, while values above 1.030 may indicate overly concentrated urine. However, like other urinalysis markers, specific gravity is interpreted alongside clinical symptoms and other test results.

Why it may be elevated

A high urine specific gravity (above 1.030) usually means the body is retaining water or the urine is very concentrated. One of the most common causes is insufficient fluid intake. During dehydration, the kidneys try to retain as much water as possible, causing urine to become concentrated and darker.

Fever, intense physical activity, vomiting, or diarrhea can also cause a temporary increase in urine concentration due to fluid loss.

High blood glucose levels can raise urine specific gravity because glucose is a heavy molecule that increases urine density. Certain hormonal conditions involving excess antidiuretic hormone (ADH) can also cause this change.

Why it may be low

A low urine specific gravity (below 1.005) is most often related to high fluid intake — a natural response when the body needs to excrete excess water.

However, persistently low specific gravity may indicate a reduced ability of the kidneys to concentrate urine. This can be associated with chronic kidney disease, where the kidneys can no longer effectively perform their concentrating function.

Diabetes insipidus — a condition where antidiuretic hormone is lacking or the kidneys do not respond to it — is characterized by very low urine specific gravity and high daily urine output. Another cause is the use of diuretic medications.

What to do next

A single deviation from normal usually does not require urgent action. It is important to consider the context: how much fluid was consumed before the test, whether there was fever, intense exercise, or other factors.

If the result deviates alongside other urinalysis changes (e.g., protein, glucose, or sediment), the doctor may recommend additional kidney function tests or blood analysis.

Improving hydration is the simplest step when specific gravity is high without an obvious cause. However, excessive water intake is also not a sensible strategy without a specialist's recommendation.

Monitoring over time

Urine specific gravity is typically tested as part of an annual or periodic urinalysis. If kidney disease or diabetes has been diagnosed, the test may be performed more frequently — according to the monitoring plan set by the doctor.

Dynamic changes — when specific gravity is consistently too high or consistently too low — are more informative than a single result. Long-term monitoring of this marker helps identify trends and respond in time.

At home, urine concentration can be roughly estimated by urine color: light yellow usually indicates normal hydration, dark yellow indicates insufficient hydration, and nearly colorless indicates high fluid intake. However, this is only an approximate observation.

Questions for your doctor

• Does my urine specific gravity result require additional kidney testing?
• What daily fluid intake would be optimal in my case?
• Could any medications I am taking affect this result?
• Should the urinalysis be repeated, and if so, after how long?
• How does this result correlate with my other urinalysis findings?