According to Georgia Highlands College, urinometers work by testing the specific gravity of a urine sample. Specific gravity is a measure of the density of a given liquid. By measuring the specific gravity of a urine sample, doctors make inferences about a patient's health and kidney function.
Urinometers feature a glass cylinder in which the urine sample is placed. Once the sample has been poured in the cylinder, a floating indicator is placed in the sample. The level at which the float sinks indicates the specific gravity of the urine. Many urinometers feature markings that indicate whether the urine sample has a low specific gravity, a moderate specific gravity or a high specific gravity. Water, which has a constant specific gravity at a given temperature, is used to calibrate a urinometer.
The amount of dissolved solids present in a urine sample alters its specific gravity. While pure water has a specific gravity of 1.0, healthy urine samples have a specific gravity between 1.005 and 1.035. Samples with a specific gravity that is lower than 1.005 indicate dilute urine, the use of diuretics or chronic renal failure. Samples that have a specific gravity of over 1.035 may indicate dehydration or diabetes mellitus.