Urine specific gravity
What it measures, and what changes the number.
Specific gravity compares the density of a urine sample with the density of pure water. It gives a quick picture of how concentrated or dilute the urine is, reflecting how much dissolved material the kidneys are putting into it relative to water.
It is part of a routine urinalysis and is read alongside the other dipstick results such as urine pH, protein, glucose and ketones, because the concentration of the sample affects how those other findings are read.
The number changes with recent fluid intake, so a first morning sample is usually more concentrated than one taken later in the day. The method matters too: dipstick pads, refractometers and urinometers can give slightly different readings, and substances such as glucose, protein or contrast dye can affect some methods. Spanish labs may print it as Densidad.
Often read alongside: Urine pH, Urine protein, Urine glucose, Urine ketones