Urine specific gravity is a measure of the concentration of particles in urine, providing insight into how diluted or concentrated it is. This measurement is a routine part of a urinalysis and offers a quick indication of kidney function and an individual’s hydration status. It compares the density of urine to the density of pure water, which has a specific gravity of 1.000. The higher the number of dissolved particles in the urine, the higher its specific gravity will be.
What Urine Specific Gravity Measures
Urine specific gravity (SG) measures the concentration of dissolved substances, or solutes, in urine relative to pure water. These solutes include waste products and electrolytes filtered by the kidneys. This measurement reflects the kidneys’ ability to concentrate or dilute urine, maintaining the body’s fluid balance.
The test is performed by collecting a urine sample, often a first-voided morning specimen. A dipstick with a color-sensitive pad provides a quick estimate. For a more precise result, a laboratory refractometer measures how much light passes through the urine, indicating its density.
In healthy adults, the normal range for urine specific gravity is between 1.005 and 1.030. Some sources narrow this range to 1.010 to 1.025. This range varies with hydration; for instance, 1.001 might be normal for someone who consumed a lot of water, while levels above 1.030 could be normal for someone with restricted fluid intake.
What Specific Gravity Results Indicate
A high urine specific gravity reading, above 1.030, indicates concentrated urine. The most common reason for elevated specific gravity is dehydration, as kidneys conserve water by producing more concentrated urine.
Fluid loss from vomiting, diarrhea, fever, or excessive sweating can also increase specific gravity. Medical conditions like uncontrolled diabetes mellitus (due to excess glucose excretion) or overproduction of antidiuretic hormone (ADH), such as SIADH, can also result in high readings.
Conversely, a low urine specific gravity reading suggests diluted urine. This can occur due to overhydration.
Low specific gravity can also indicate kidney disorders where kidneys lose their ability to concentrate urine, leading to large volumes of dilute urine. Conditions like diabetes insipidus (affecting water management) or kidney infections like pyelonephritis may present with low urine specific gravity.
Urine specific gravity results are one piece of information in a comprehensive health assessment. A healthcare professional should interpret these results within the context of a person’s overall health, other symptoms, and additional diagnostic tests. A single reading does not provide a definitive diagnosis, but signals the need for further investigation.