Refractometer: Testing Urine

A refractometer is an instrument that measures how light bends as it passes through a sample. The degree to which a sample bends light is correlated to the number and size of solute particles. When a refractometer tests a urine sample, it measures the specific gravity of the urine.

The urine's specific gravity indicates the kidneys’ ability to balance water content and excrete waste. Typical values range between 1.005 to 1.030. A low specific gravity suggests an inability to concentrate urine, excessive hydration, or diabetes insipidus. A high specific gravity could indicate dehydration or diabetes mellitus.

Image A shows a refractometer. It is a cylinder shape with a flap at one end, which the sample goes under. Image B shows the scale, which can be viewed from the other end of the refractometer.

Figure 1: A) A Refractometer has two ends: one for the sample and the other for looking at the display. B) The refractometer display is visible when you look through the wider end of the refractometer. The display shows the urine's specific gravity.